Programming in Delphi

Introduction

The Delphi language was formerly known as Object Pascal, and is an object-oriented version of the venerable Pascal language, combined by Borland with a Visual Basic-like RAD tool that lets you write fast GUI applications with no run-time, a very rich set of components (VCLs) that can be statically compiled into the EXE, and an encapsulation of most of the Windows API for easier access to the underlying OS. If this reminds you of .Net, it's no chance since both Delphi and the .Net framework were designed by the same person, Anders Hejlsberg. For more infos, read Delphi history – from Pascal to Diamondback (Delphi 2005) by Zarko Gajic.

As of April 2005, Delphi is available as Delphi 2005, a.k.a. Delphi 9, to write Win32 or .Net applications, but you might be able to still get your hands on Delphi 7 (to write Win32, and Linux applications by using Kylix and the Qt widgets-based CLX component library instead of the Windows-only VCL widgets), or Delphi 8 (to get you started writing .Net applications; D7 has a command-line version of the Delphi CLI compiler, but it was really meant as a learning tool.) Note that D8 comes with Delphi 7.1. Delphi 2005 supports the 1.1 .Net framework.

Setup

If you just want to get started and learn Delphi, the $99 Personal edition of Delphi 7 is all you need is love. If you prefer to start developing for .Net, try Delphi 9, a.k.a. Delphi 2005. In October 2006, Borland relaunched its Turbo brand, and offers two versions: Explorer, which are free but doesn't allow installing third-party components, and Professional, which aren't. Turbo Delphi Win32 is Delphi 2006 (a.k.a. Borland Developer Studio) with just the Delphi for Windows32 personality.

FWIW, the main extras offered by the Enterprise version of Delphi 7 are IntraWeb from AToZed (Framework + component set for building web apps in a RAD manner), Rave Visual Designer (Visual reporting tool), BizSnap (to create web services,) and Model Maker (UML stuff.)

IDE

  1. Create shortcut on desktop, with Start In = where you save your projects
  2. Install the latest Update and hot-fixes
  3. Get rid of news: Tools > Env't Options > Delphi Direct: Uncheck "Automatically poll network".
  4. Combine Object TreeView, Object Inspector, Project Manager
  5. Remove useless toolbars
  6. Hide line numbers and gutter
  7. Save desktop
  8. Install CnWizards
  9. Install GExperts
  10. Install memory-related add-on's: FastMM, madExcept ("replaces Delphi's exception handling with a much more intelligent solution"), MemProof ("FREE heap memory and resource 'leak' debugger for Borland's 32-bit family of compilers")
  11. Install third-party components
  12. DOESN'T WORK (D2007) Disable Welcome Page (HKEY_CURRENT_USER\Software\Borland\BDS\5.0\Known IDE Packages\Delphi\$(BDS)\Bin\startpageide100.bpl)
  13. (D2007) Install DDevExtensions to get TAB/Shift-TAB indenting
  14. (D2007) Remove Welcome Page (set HKEY_CURRENT_USER\Software\Borland\BDS\<version #>\Known IDE Packages\Delphi\$(BDS)\Bin\startpageide100.bpl to empty string)
  15. (D2007) Set the default directory to save new projects by editing HKEY_CURRENT_USER\Software\Borland\BDS\5.0\Globals\DefaultProjectsDirectory

How to add bookmarks?

To add bookmarks to source code so you can jump to locations, press CTRL-SHIFT, and any number between 0 and 9.

To jump to that location, hit CTRL and the number of the bookmark (doesn't work in D7 with default settings). Or you can use CnWizards, and hit CTRL-SHIFT-B to get a list of bookmarks.

Can I indent a block of code in one go?

If you'd rather use the familiar TAB button to indent a whole block, install Two Desk's Castalia add-in to the IDE, or the free CnWizards (a.k.a. CnPack IDE Wizards).

Can I comment a whole block in one go?

If you are running Delphi Pro and above, check out GExperts or CnWizards. If you are using the Personal or Standard edition, looks like the only way is to use the { and } syntax, with no menu or keyboard shortcut available.

Recommended components and packages

Some are open-source, some are just freeware, and yet others are commercial:

Sites to check for Delphi components

Must-have third-party tools

Delphi in a nutshell

Components and packages

Note: In the Delphi literature, depending on the context, "package" refers to either a DPK master file and PAS/DCU source files, or the resulting, compiled BPL file which contains all the DCU files.

Components can be distributed either as

Typically, commercial components are provided as binary files, but some can also be bought with source files.

Individual components (ie. PAS or DCU files) can be added to an existing package, or to a brand new package through either File > Open (select a DPK file, click on Add, and compile) or Component > Install Component (when adding to an existing package, the default file is DCLUSR.DPK).

A package file has the extension BPL, and is just a Borland-specific version of a DLL with added functions like GetPackageInfoTable(), ie. routines that live in a file separate from the caller EXE, and that can be loaded dynamically when needed. Use the Bin\TDUMP.EXE command-line Borland utility to display information containted in a BPL file.

Once installed, packages are listed in the Registry under HKEY_CURRENT_USER\Software\Borland\Delphi\<version>\Known Packages . For Delphi to find components, they must be located in known directories through the Tools > Environment Options > Library.

Packages come in three different forms:

Components meant to be used in the IDE can only be installed as a package, ie. a DPK master file along with one or more PAS files to be compiled into DCUs and aggregated in a single BPL file that will be registered into the IDE.

Note that design-time packages and run-time packages are two different beasts: The former adds itself to a palette in the IDE and provides an interface to access its properties, routines, and events; The latter is used by applications that were compiled with run-time packages, ie. dynamic linking. Some BPLs are both design-time and run-time, so I guess they have a switch somewhere in the code that lets me act differently depending on the context.

From what I understand, a typical situation is thus:

Depending on the "Build with runtime packages" checkbox in Project > Options > Packages, the compiler will either (if disabled) include all the DCU files into the EXE, or (if enabled) use an external BPL file, that you'll have to distribute in addition to the EXE. In other words, this is where you decide whether to link third-party components statically into the EXE, or dynamically by loading BPLs at run-time.

If the packages don't change often, it might be a good idea to use dynamic linking, so that you only need to distribute the EXE for updates. On the other hand, dynamic run-time packages contain all the routines, even those that your EXE doesn't use, while, when using statically-linked packages, the IDE will only include stuff that your EXE actually use. In the end, a statically-linked EXE can turn out to be smaller that a bare EXE and external BPLs.

Finally, if resource files are used (RES or DCR), Delphi will need those to compile a package successfully. Bitmaps for the components that will appear in the palette are saved in the DCR files.

The source files, either source (.PAS) or compiled (.DCU) aren't needed to use a component; They are only needed if you want to compile the component yourself.

Important: As DCUs are version-dependent, a package can only be installed in the same version of the IDE that was used to compile it. That's the reason why some components are distributed as source code that you must compile yourself into a package before adding it to the IDE. The alternative for commercial components is to generate multiple versions of the package, one for each version of the IDE that they wish to support.

Moving a design package to another host requires copying the following files: BPL, DCP, possibly DCR resources files, hitting the Component > Install Packages menu, and clicking on Add.

In addition to individual packages, it is possible to create a package collection (DPC) to make it easier to distribute the different files that make up a package. A DPC will contain DCP, DCU, and BPL files. This type of file requires a Package Collection Editor (PCE), which is a source file used to define a DPC file. A DPC file is created through Tools > Package Collection Editor.

More information:

Questions

Making sense of extensions

Extension

Acronym

Role

PAS

Pascal

Source code; Like .C in C

DCU

Delphi Compiled Unit

Compiled version of .PAS files; Similar to .OBJ file in C

DFM

Delphi Form

Describes a form, and what it contains

DPR

Delphi Project

EXE project master file

RC

Resource

Clear-text resource file

RES

Resource

Binary resource file from RC

DRC

Delphi Resource

Compiler-generated resources. Usually strings; it's pretty much a .RC file without a correspondent .RES

DCR

Delphi Component Resource

Resource files; Includes bitmaps used for components added to the IDE

INC

Include?

Source code; Like .INC in C

 

 

 

DCP

Delphi Compiled Package

Used for EXEs built with run-time BPLs to let the compiler know how to link to the BPL at run-time; Doesn't include compiled code, which is stored in DCU or BPL files

BPL

Borland Package Library

Delphi-specific DLL, ie library loaded at run-time

DPK

Delphi Package ???

Project master file when developing a package; equivalent to .DPR for EXE projects

DPC

Delphi Package Collection

?

DPKW

 

Like DPK

 

 

 

BPG

Borland Project Group

Used to keep track of projects when opening more than one project in the IDE

BPK

?

?

BPI

?

?

 

 

 

CFG

Compiler Configuration

Compiler settings; Similar to DOF

DOF

Delphi Options File?

Project options

DSK

Desktop

Desktop settings

 

 

 

 

 

 

 

 

 

 

 

 

Menus of interest

Getting started

Skeleton of a source file

A typical Delphi GUI program is a set of units (*.PAS) which contain source code, and are listed in a project (.DPR file), while the forms (windows) are described in files with the DFM extension, ie. DPR = PAS + DFM.

Here's a skeleton of a unit:

//Name of the unit, which can then be referenced in other source files (a unit name must be unique within a project)
unit Unit1;
 
//List of public stuff, eg. variables that can be accessed from other source files
interface
 
uses  { List of units goes here }
 
  { Interface section goes here }
 
//Actual code of this source file
implementation
 
uses  { List of units goes here }
 
  { Implementation section goes here }
 
initialization
  { Initialization section goes here }
 
finalization
  { Finalization section goes here }
 
//A source file must end with "end."
end.

Hello, world! (console)

Open your favorite editor, save the file as console.pas, and copy/paste the following code:

program Console;
 
{$APPTYPE CONSOLE}
 
var MyMessage: string;
 
begin
  MyMessage := 'Hello world!';
  Writeln(MyMessage);
end.

Open a DOS box, compile the program with "dcc32.exe console", and run the compiled as with "console.exe".

Hello, World! (GUI)

In the empty form that shows up when starting Delphi, add a label and a pushbutton, double-click on the button, and add the following code to the Button1Click() routine:

Label1.Caption := 'Hello, world!';

Hit F9 to run the application, and click on the pushbutton to see the text of the label change.

Showing a message box with a  default button

With D7 at least, Delphi's MessageDlg doesn't let you select a default button, which is unfortunate for critical choices. You'll have to use Win32's MessageBox() instead:

if MessageBox(Handle,'text','caption',MB_OKCANCEL or MB_ICONQUESTION or MB_DEFBUTTON2 ) = IDCANCEL then begin
    exit;
end else begin
    ShowMessage('ok');
end;

Dynamic objects

When you add a control on a form at design-time, Delphi takes care of creating and freeing the object, but those tasks are your responsibility when creating objects dynamically, at run-time.

The important point is freeing the object from memory, or your application will leak memory.

There are three ways to handle this:

Declare a variable, call the class' Create() method, and end with Free(), preferably in a try/finally structure:

var
    MyObj : TObj;
begin
    with TObj.Create(nil) do
        try
            //Do stuff
        finally
           Free;
    end;

A second way is to use the With structure, and set the instance's owner as a form, so that, even if you forgot to call Free, Delphi will free the object from memory when it kills the parent form (Actually, you should NOT call Free, and let the owner free the instance from memory):

var
    MyObj : TObj;
begin
    with TObj.Create(Self) do begin
        //Do stuff
    end;

Note that the time to dynamically create components with owners is much slower than that to create components without owners.

A third way is to use the With structure with Nil as the parent, but in this case, Free() must be called explicitely:

with TObj.Create(nil) do
    try
        //Do stuff
    finally
       Free;
    end;
end;

Checking for memory leaks

Since D2006, Delphi includes a way to check for memory leaks in the IDE once the application has terminated. To enable this, just add the following line in the Project's DPR file (via Project > View Source):

begin
  ReportMemoryLeaksOnShutdown :=true;
  Application.Initialize;

Here's an example to trigger an error:

procedure TForm1.Button1Click(Sender: TObject);
var
  MySL : TStringList;
begin
  MySL := TStringList.Create;
end;

Reading from a text file

Here, we'll read the file line by line:

procedure TForm1.Button1Click(Sender: TObject);
var
  myFile : TextFile;
  text   : string;
  bit : string;
begin
  AssignFile(myFile, 'C:\test.txt');
  try
    Reset(myFile);
    while not Eof(myFile) do
    begin
      ReadLN(myFile,bit);
      text := text + bit + #13#10;
    end;
  finally
    ShowMessage(text);
    CloseFile(myFile);
  end;
 
end;

A faster way:

function LoadFile(const FileName: TFileName): string;
begin
  with TFileStream.Create(FileName, fmOpenRead or fmShareDenyWrite) do begin
    try
      SetLength(Result, Size);
      Read(Pointer(Result)^, Size);
    except
      Result := '';  // Deallocates memory
      Free;
      raise;
    end;
    Free;
  end;
end;
 
FileContents := LoadFile('rss.xml');

ExtractFileDir() in a DataModule?

Application is declared in the forms unit.  As an alternative you can change "Application.ExeName" to "ParamStr(0)".

Reading from a tab-delimited file

Here's how to read each line of a tab-delimited text file, and save this into an SQLite database:

With ASQLite3DB1 do begin
    DefaultDir := ExtractFileDir(Application.ExeName);
    Database := 'test.sqlite';
    CharacterEncoding := 'STANDARD';
    Open;
    SQLite3_ExecSQL('CREATE TABLE IF NOT EXISTS mytable (id INTEGER PRIMARY KEY, label VARCHAR)');
end;
 
AssignFile(SomeTxtFile, FILE2PARSE) ;
Reset(SomeTxtFile) ;
ASQLite3DB1.SQLite3_ExecSQL('BEGIN;');
 
while not EOF(SomeTxtFile) do begin
    ReadLn(SomeTxtFile, buffer) ;
 
    PerlRegEx1.RegEx := '^([^d].+)\s(\d+)$';
    PerlRegEx1.Options := [preCaseLess];
    PerlRegEx1.Subject := buffer;
    If PerlRegEx1.Match then begin
        row := Format('INSERT INTO mytable (id,label) VALUES (%s,"%s");',[PerlRegEx1.SubExpressions[2],PerlRegEx1.SubExpressions[1]]);
        ASQLite3DB1.SQLite3_ExecSQL(row);
    end;
end;
 
ASQLite3DB1.SQLite3_ExecSQL('COMMIT;');
ASQLite3DB1.Close;
CloseFile(SomeTxtFile);

Writing into a text file

var
  myFile : TextFile;
  letter : char;
  text   : string;
 
begin
  AssignFile(myFile, 'Test.txt');
  ReWrite(myFile);
 
  WriteLn(myFile, 'Hello, world!');
 
  CloseFile(myFile);
end;

Alternatively:

procedure SaveFile(const FileName: TFileName; const content: string);
begin
  with TFileStream.Create(FileName, fmCreate) do
    try
      Write(Pointer(content)^, Length(content));
    finally
      Free;
    end;
end;

Rewinding a text file

Here's how to set the cursor back to the beginning of a text file, ie. not a binary file that uses records:

var
    dummy : TextFile;
 
begin
    AssignFile(dummy, 'dummy.txt');
 
    ReWrite(dummy);
    WriteLn(dummy, '123');
 
    ReWrite(dummy);
    WriteLn(dummy, '345');
 
    CloseFile(dummy);

Here's another way :

var
    test : TFileStream;
    status : String;
 
begin
    status := 'test';
 
    test := TFileStream.Create('test.txt',fmCreate);
    test.Write(Pointer(status)^,Length(status));
    test.Seek(0, soFromBeginning);
    test.Free;

Playing with radio buttons

At design-time, the best way to add radio buttons to a form is by first adding a radiogroup object, and modify its Items property to add radio buttons.

Here's how to display the radio button currently selected, if any:

  ShowMessage(Radiogroup1.Items.Strings[RadioGroup1.ItemIndex]);

A more complicated way:

  for Index := 0 to RadioGroup1.Items.Count - 1 do begin
    if RadioGroup1.ItemIndex = Index then begin
      ShowMessage(RadioGroup1.Items[Index]);
    end;
  end;

Here's how to clear it:

RadioGroup1.ItemIndex:=-1;

Playing with TStringList hashed arrays

In addition to indexes, a TStringList array can use names so as to build name=value items. Here are some examples:

var
    indexclassifications : TStringList;
    i : Integer;
 
begin
    indexclassifications := TStringList.Create;
 
    indexclassifications.Add('unix=good');
    indexclassifications[0] := 'windows=bad';
 
    for i := 0 to indexclassifications.Count-1 do begin
        ShowMessage(indexclassifications[i]);
        ShowMessage(indexclassifications.Names[i]);
 
        ShowMessage(indexclassifications.ValueFromIndex[i]);
        ShowMessage(indexclassifications.Values[indexclassifications.Names[i]]);
    end;
 
    indexclassifications.Free;

An alternative is Ciaran McCreesh's Hash Library.

Playing with a ListBox

Adding items

ListBox1.Items.Add('Hello');

Adding an item at a specific location in the list

ListBox1.Items.Insert(3,'Hello');

Reading the item that was double-clicked

procedure TForm1.ListBox1DblClick(Sender: TObject);
var
  listBox : TListBox;
  index   : Integer;
begin
  listBox := TListBox(Sender);
  index   := listBox.ItemIndex;
  ShowMessage(listBox.Items[index]);
end;

Selecting a directory

Here's how to display a dialog box so the user can choose a directory:

procedure TForm1.Button1Click(Sender: TObject);
var
  chosenDirectory : string;
  options : TSelectDirOpts;
 
begin
  chosenDirectory := 'C:\';
  if SelectDirectory(chosenDirectory, options, 0) then
    LabeledEdit1.Text :=chosenDirectory + '\';
 
end;

Closing an application

Two possibilites, using either Sys.Close() or Application.Terminate(), but the latter doesn't trigger the onClose or onCloseQuer events:

//If app already ran, make the button Close the app
If (Button1.Caption = 'Close') then begin
    Close;
    Exit;
end;

Downloading a web page into a variable

Moved to Internet Development with Indy components

Removing unwanted characters

Here's how to strip unwanted characters from a string:

function CleanInput(input : String) : String;
var
  output : string;
  index : Integer;
begin
  output := StringReplace(input, #9, '',[rfReplaceAll, rfIgnoreCase]);
  output := StringReplace(output, #10, '',[rfReplaceAll, rfIgnoreCase]);
  output := StringReplace(output, #13, '',[rfReplaceAll, rfIgnoreCase]);
  output := StringReplace(output, '  ', '',[rfReplaceAll, rfIgnoreCase]);
  output := StringReplace(output, '&nbsp;', '',[rfReplaceAll, rfIgnoreCase]);
  output := StringReplace(output, '&nbsp', '',[rfReplaceAll, rfIgnoreCase]);
  output := StringReplace(output, '<br>', '',[rfReplaceAll, rfIgnoreCase]);
  Result := output;
end;

PINGing a server

Here's how to do it using the open-source ICS tools:

procedure TForm1.Timer1Timer(Sender: TObject);
begin
  Ping1.Address := '127.0.0.1';
  Ping1.Ping;
end;
 
procedure TForm1.Ping1EchoReply(Sender, Icmp: TObject; Status: Integer);
begin
  if Status <> 0 then
      { Success }
      Label1.Caption := 'Server ' + Ping1.HostIP + ' alive @ ' + TimeToStr(Time)
  else
      { Failure }
      Label1.Caption := 'Server ' + Ping1.HostIP + ' dead @ ' + TimeToStr(Time) +
        #13#10 + Ping1.ErrorString + '. Status = ' + IntToStr(Ping1.Reply.Status);
end;  

Here's how to do it using Indy 9 (? The one that ships with Delphi 7):

Moved to Internet Development with Indy components

Checking the class of an object

If you need to display the class of an object:

ShowMessage(MyObj.ClassName);

Casting an object

Sometimes, it's necessary to help Delphi by casting an object:

//Otherwise, E2010 Incompatible types: 'TMemoryStream' and 'TStream'
PerlRegEx1.Subject := StreamToText(TMemoryStream(RcvdStream));

Playing with date and time

Here's how to time tasks:

var
  StartTime,StopTime : TDateTime;
begin
  StartTime := Now;
  ListBox1.Items.Add (TimeToStr (StartTime));
 
  [...]
 
  StopTime := Now;
  ListBox1.Items.Add('After doing stuff ' + FormatDateTime ('hh:nn:ss', StopTime - StartTime));

More information:

Reading caller ID information through a modem

Using the Treeview control

TreeView1.LoadFromFile('myTABBEDfile.txt');

Using the Listview control

(stolen from D7's help file)

procedure TForm1.PopulatClick(Sender: TObject);
const
  Names: array[0..5, 0..1] of string = (
    ('Rubble', 'Barney'),
    ('Michael', 'Johnson'),
    ('Bunny', 'Bugs'),
    ('Silver', 'HiHo'),
    ('Simpson', 'Bart'),
    ('Squirrel', 'Rocky')
    );
 
var
  NewItem : TListItem;
  ListItem : TListItem;
  ListView: TListView;
  NewColumn: TListColumn;
  I: Integer;
 
begin
  with ListView1 do
  begin
    ViewStyle := vsReport;
    RowSelect := True;
 
    NewColumn := Columns.Add;
    NewColumn.Caption := 'Last';
    NewColumn := Columns.Add;
    NewColumn.Caption := 'First';
 
    for I := Low(Names) to High(Names) do begin
      ListItem := Items.Add;
      ListItem.Caption := Names[I][0];
      ListItem.SubItems.Add(Names[I][1]);
    end;
  end;
 
end;

Arrays

Delphi supports static and dynamic arrays. To make things a bit confusing, it uses the same syntax "array of" to declare dynamic arrays, and so-called "open arrays", ie. arrays (either static or dynamic) passed as parameters to a routine.

Dynamic arrays are really a one-dimensional array that holds pointers to other arrays, and each cell can point to arrays of different dimensions:

SetLength(MyArray[3],15); //Array[3] points to a fifteen-column array
SetLength(MyArray[2],5); //Array[2] points to a five-column array

As a result, Delphi cannot provide VisualBasic's UBound(MyArray,x) where x is either 1, 2, or 3, and High(MyArray) returns the upper bound of the array. If one of the cells in the array uses a different dimension from the other cells, you'll have to call High(MyArray[thiscell]) to get is upper bound.

Here's an example:

type
    TDigits = array of array of Integer;
 
procedure MyFunc(A: TDigits);
begin
    //4
    ShowMessage(IntToStr(High(A)));
    //9
    ShowMessage(IntToStr(High(A[0])));
    //6
    ShowMessage(IntToStr(High(A[2])));
end;
 
[...]
 
var
    MyArray : TDigits;
begin
    SetLength(MyArray,5,10); //5 rows, 10 columns each
    SetLength(MyArray[2],7); //We can use a different dimension for one cell
 
    MyFunc(MyArray);
end;

"Arrays can be allocated statically or dynamically.

Static arrays:

var MyArray: array[1..100] of Char;

Dynamic arrays:

var MyFlexibleArray: array of Real;
SetLength(MyFlexibleArray, 20);

To deallocate a dynamic array, assign nil to a variable that references the array or pass the variable to Finalize; either of these methods disposes of the array, provided there are no other references to it. Dynamic arrays are automatically released when their reference-count drops to zero."

"If X and Y are variables of the same dynamic-array type, X := Y points X to the same array as Y.

Unlike strings and static arrays, COPY-ON-WRITE is not employed for dynamic arrays, so they are not automatically copied before they are written to. In contrast, to make an independent copy of a dynamic array, you must use the global Copy function."

"In some (???) function and procedure declarations, array parameters are represented as array of baseType, without any index types specified. For example,

function CheckStrings(A: array of string): Boolean;

This indicates that the function operates on all arrays of the specified base type, regardless of their size, how they are indexed, or whether they are allocated statically or dynamically. See Open array parameters."

If you need to pass an array to a routine, you cannot set its size directly, ie.

procedure Sort(A: array[1..10] of Integer); //error

won't work. Instead, you must either create a type...

type TDigits = array[1..10] of Integer;
procedure Sort(A: TDigits);

...or use open arrays. Open array parameters allow arrays of different sizes to be passed to the same procedure or function:

procedure Add(A: array of Integer);
 
;Note: open arrays are always zero-based., regardless of which Low() you chose to declare the array.
;ie. array[1..4] of Integer won't work as intended
 
procedure MyCallingFunction;
    var Temp: array[0..3] of Integer;
 
    Temp[0] := 5;
    Temp[1] := 7;
    Temp[2] := I;
    Temp[3] := I + J;
 
    Add(Temp);
end;

To read:

Associative array ("hash")

You can use Delphi's TStringList object:

var
  myhash : TStringList;
  Index : Integer;
 
begin
  myhash := TStringList.Create;
  myhash.Add('mykey=myvalue');
  myhash.Add('mykey2=myvalue2');
 
  ShowMessage(myhash.Values['mykey']);
 
  for Index := 0 to myhash.Count-1 do begin
    ListBox1.Items.Add(myhash.Names[Index] + '=' + myhash.ValueFromIndex[Index]);
  end;
  myhash.Free;
end;

Alternative:

"https://svn.openxp.de/openxp/trunk/xplib/hashes.pas

Here's unit with those TIntegerHash and TStringHash, described @ http://www.undu.com/Articles/020604.html

Usage of it is really simple! Just add 'hashes' (filename of .pas file) to uses clause and then somewhere in code write:

var
  hash : TStringHash;
begin
  hash := TStringHash.Create;
  try
    hash['one'] := 'viens';
    hash['two'] := 'divi';
    ShowMessage(hash['one']);
    ShowMessage(hash['two']);
  finally
    hash.Free;
  end;

"

Delphi and databases

The big picture

BDE

BDE + SQL Links or ODBC

DB-agnostic solutions: dbExpress (read-only -> ClientDataSet/Provider), dbGo/ADOExpress

DB-specific connectors (ZeosLib, Interbase Express/IBX or Interbase Objects/IBO, etc.)

Note: IBX's IBTable, IBQuery/IBUpdateSQL, and IBStoredProc are intended for compatibility with older BDE components. For new applications, you should generally use the IBDataSet component, which allows you to work with a live result set obtained by executing a select query. It basically merges IBQuery with IBUpdateSQL in a single component.

Using an IBQuery that hosts the SQL select statement together with an IBUpdateSQL component that hosts the insert, update, and delete SQL statements is a typical approach from BDE applications.

ClientDataSet/MyBase (requires the entire table to be loaded in memory to access even a single record)

Multi-tier with DataSnap (formerly known as Middle-tier Distributed Application Services, or MIDAS)

BlackFish SQL

DB, query/table datasets, datasource, DBGrid, UpdateSQL

Transactions

 

Query/Table: Dynamic (created by component) vs. persistent (createad a designtime through Fields editor) fields

Query: Params vs. FieldsByName/Fields?

Query/UpdateSQL: Why both?

SELECT+Open, INSERT/UPDATE/DELETE + ExecSQL

 

Regular SQL vs. parametric queries: When you need slightly different versions of the same SQL query, instead of modifying the text of the query itself each time, you can write a query with a parameter and change the value of the parameter, eg. "select * from employee where job_country = :country".

Notice that all the data-aware components are unrelated to the data-access technology, provided the data-access component inherits from TDataSet.

DBLookupListBox or DBLookupComboBox. The DBLookupComboBox component can be connected to two data sources at the same time: one source containing the data and a second containing the display data.

Datasets: You can modify data in the active buffer only after you explicitly declare you want to do so, by giving the Edit command to the dataset. You can also use the Insert command to create a new blank record and close both operations (insert or edit) by giving a Post command.

To access data from the active record, use the dataset' Field components, which are by default automatically created when a dataset component is created. These field components are stored in the dataset's Fields array property. You can access these values by number (accessing the array directly) or by name (using the FieldByName method). Each field can be used to read or modify the current record's data by using its Value property or type-specific properties such as AsDate, AsString, AsInteger, and so on.

Note: When you set field properties related to data input or output, the changes apply to every record in the table. When you set properties related to the value of the field, however, you always refer to the current record only.

Creating the field components each time a dataset is opened is only a default behavior. As an alternative, you can create the field components at design time, using the Fields Editor.

The VCL includes a number of field class types. Delphi automatically uses one of them depending on the data definition in the database, when you open a table at run time or when you use the Fields Editor at design time.

Types of fields: Data, Calculated (OnCalcFields event), Lookup

Add field (from database) vs. New field (created manually in dataset): Note that fields that are created at design-time with the Fields Editor are the only ones that will be available at run time (Fields, FieldByName). When a program opens a table at run time, if there are no design-time field components, Delphi creates field objects corresponding to the table definition. If there are some design-time fields, however, Delphi uses those fields without adding any extra field objects.

A TField component has both a Name property and a FieldName property. The Name property is the usual component name. The FieldName property is either the name of the column in the database table or the name you define for the calculated field.

Tip: You can also drag the fields from the editor to the form to let the IDE create visual components for you. This is a handy feature that can save you a lot of time when you're creating database-related forms.

When you operate on a dataset in Delphi, you can work in different states. These states are indicated by a specific State property, which can assume several different values.

DBGrid.Columns to customize how columns work

Master/detail

Transactions

Error handling: if ComboName.Text = '' then raise Exception.Create ('Insert the name');

Datamodule

There are two ways to refer to a record in a dataset: Use a TBookmark/TBookmarkStr to save a reference to the current record, or use the Locate method to find a record that matches given criteria.

To navigate through a dataset, you can use First/while not EOF/Next. Remember to use DisableControls/EnableControls to speed things up when going through a lot of records. An even better method is to let the SQL server do most of the work.

To make changes to each record, use a "while not EOF" loop that contains a call to dataset.Edit, mycolumn.Value=, dataset.Next (Next means that the change will be posted).

Here's how to fill a regular combobox with stuff from a dataset:

//Here, SELECT data from the database
cds.Open;
while not cds.Eof do begin
    ComboName.Items.Add (cdsName.AsString);
    cds.Next;
end;

When is UpdateSQL required? Typically, TQuery and like query components only allow you to specify a Select statement and it then figures out from that how to build insert, update, and delete statements. But this ability is fairly limited, it does not take much to write a Select statement that it cannot deal with (joins, sub-selects, unions, etc). In this case, the TQuery is read-only. Corresponding TUpdateSQL components allow you to specify the insert, update,  and delete statements corresponding to such selects.

Dataset.Edit/Post

Dataset.InsertRecord ([ComboName.Text, EditCapital.Text, ComboContinent.Text, EditArea.Text, EditPopulation.Text]);

Other stuff

Just like Microsoft development tools, for historical and technical reasons, Delphi provides different ways to connect to a database. You should choose a solution depending on how big the database is, and whether you have the luxury of choosing a specific database engine or the application must be database-agnostic:

As of 2008, the recommended choice is either DB-specific connector or dbExpress.

Overview

Basically, if you need DB-agnostic solutions, use either ADO or dbExpress. If you don't mind being tied to a given DB engine, use DB-specific solutions like connectors to SQLite, MySQL, FireBird, etc.

BDE

Historically, the first means offered by Delphi to connect to a database was the IDAPI(Independent Database Application Programming Interface). As it never acquired the popularity of Microsoft's ODBC, it was turned into BDE (Borland Database Engine).

The BDE uses a collection of DLL's, each one specific to the database that the application wants to connect while presenting a common API to the application:

Data (local or remote) < Database engine (BDE, etc.) < Dataset < Datasource < DB* visual components

Until 1997, BDE was the only way for Delphi applications to connect to database, but it fell in favor because it's a bit heavy to deploy, and doesn't offer good performance over remote connections

The BDE has a long and glorious history. It originated in Delphi 1 as an engine for accessing Paradox databases and was later part of the ISAPI initiative involving IBM, Novell, and WordPerfect. Despite a few problems, the BDE is one of the reasons for Delphi's success in the database arena and, having reached version 5, it is a mature technology.
 
So why move away from the BDE? Deploying it on rented Internet servers is often impossible because of ISPs' concerns about running system-level services on their servers. Although the BDE has been updated to support features like the Oracle 8 object-relational model, some of its features are still bound to its Paradox roots. Another problem is that the BDE includes the entire engine used by Paradox and dBase to access data. There is no way to deploy a thin version of the BDE excluding Paradox support if you are targeting only SQL servers. (On the other hand some of these problems, such as running SQL Server on an ISP's server, apply to using ADO as well.)
 
The BDE also does local caching but won't allow you to interact with it. However, a few Delphi programmers have learned to use the ClientDataSet component to operate on cached data.
 
Despite being freely distributed with Borland’s popular line of application development tools, the BDE was unpopular because of complexities in installation and poor performance. As Delphi became one of the leading application development tools for the Windows platform, individuals and companies proposed alternative interfaces to the BDE. These “BDE Alternatives” optimized access to the database by directly using the native database driver, providing performance and feature advantages with respect to the BDE.
 
The common denominator for database access in Delphi is no longer the BDE. Instead, it's the TDataset class.
 
TTables = Delphi's desktop database components; Inefficient in a client/server environment.
 
The reason there is both a TTable and a TQuery component is due to the fact there table-oriented databases like Dbase, Paradox, or Access, and there are set-oriented databases like Interbase, Oracle, and MSSQL.
 
Delphi's database architecture has not changed significantly since Delphi 3 introduced the abstract TDataSet class to make custom datasets fully integrated with the dataset/data-aware architecture, that up to Delphi 2 was tied only to the BDE datasets.
 
From D3 onwards all BDE functions were removed from TDataset making it independant of any DB format.
 
What TDataset isn't - TDataset has no:
  • SQL support
  • DB session control functions
  • inherent links to any DB
  • No index support
  • No range setting
  • No master-detail linking

(From D2007 PDF) "TUpdateSQL Lets you use cached updates support with read-only datasets.

Connecting to another dataset. Client datasets can work with data provided by another dataset. A TDataSetProvider component serves as an intermediary between the client dataset and its source dataset. This dataset provider can reside in the same data module as the client dataset, or it can be part of an application server running on another machine. If the provider is part of an application server, you also need a special descendant of TCustomConnection to represent the connection to the application server.

Client datasets provide the most robust way to work with cached updates. By default, other types of datasets post edits directly to the database server. You can reduce network traffic by using a dataset that caches updates locally and applies them all later in a single transaction. For information on the advantages of using client datasets to cache updates, see Using a client dataset to cache updates

Client datasets can apply edits directly to a database server when the dataset is read-only. When using dbExpress, this is the only way to edit the data in the dataset (it is also the only way to navigate freely in the data when using dbExpress). Even when not using dbExpress, the results of some queries and all stored procedures are read-only. Using a client dataset provides a standard way to make such data editable.

In addition to these specialized client datasets, there is a generic client dataset (TClientDataSet), which does not include an internal dataset and dataset provider. Although TClientDataSet has no built-in database access mechanism, you can connect it to another, external, dataset from which it fetches data and to which it sends updates.

Typically, an application checks the dataset state to determine when to perform certain tasks. For example, you might check for the dsEdit or dsInsert state to ascertain whether you need to post updates.

dbGO/ADO Express

If you don't mind depending on Microsof's MDAC layer, you can use the ADO page of components

ActiveX Data Objects (ADO) is part of Microsoft's Universal Data Access initiative. It provides a simplified framework for data access based on OLE DB, the real power horse behind the scene. Programming directly for the OLE DB layer is complicated so Microsoft has provided a simpler solution.
 
In providing the ADOExpress technology in Delphi, Borland has accepted ADO as a common technology and has also acknowledged Microsoft's Access as a widespread database engine. Just as the BDE includes some Paradox-related features, ADO includes several features which are more Access-oriented than a universal data access solution should provide.

dbExpress/DBX/DataSnap Direct

Otherwise, you can use dbExpress, which offers very good performance because it's unidirectional. This means that you'll need to use a ClientDataSet component (located in the Data Access page) to navigate through a cache and be able to use DB* visual components. Components in the Data Access page can be used with any data access solution, and include TClientDataset, which can work with data stored on disk or, using the TDataSetProvider component also on this page, with components from one of the other groups.

Note that in recent version of Delphi, dbExpress' TSQLClientDataset was replaced by TSimpleDataset, which is meant for two-tier architectures. TSimpleDataSet is really the combination of TDataSetProvider + TClientDataSet. To update the SQL database, use the ClientDataSet's ApplyUpdates(), that you can call in the DB-control's AfterPost event.

Database > dbExpress driver > TSQLConnection > TSQLDataSet > TSQLDataSetProvider > TClientDataSet > TDataSource > DB* visual components

Realizing the limitations of the BDE, Borland proposed a new type of database interface called dbExpress. This interface was designed to broker access between Delphi and virtually any relational database through 3rd party drivers. Borland significantly improved the performance of dbExpress with respect to the BDE, but the implementation was buggy and supported only a limited subset of SQL that hampered functionality.
 
dbExpress - a.k.a. DataSnap Direct - is Borland's new cross-platform data access layer. Does dbExpress allow access to file based databases such as DBase, Paradox and FoxPro? No. It currently works with DB2, Interbase, MySQL and Oracle.
 
Unlike the BDE, dbExpress returns only unidirectional cursors and therefore does no caching. The MIDAS ClientDataset can be used for caching, and scrolling, indexing, and filtering on the result set.
 
In 2000, Borland introduced a new SQL driver architecture called "dbExpress." dbExpress is designed to deliver ultra high performance data access and simplify deployment and configuration of SQL drivers. dbExpress is a pure SQL driver architecture and does not use BDE technology. This new driver architecture replaces the SQL data access functionality of the "older" BDE SQL Links combination, but does so without the runtime and deployment overhead of the BDE. Developers have the option of using either InterBase Express (IBX) or dbExpress to access local InterBase tables.

DataSet

Table, Query, StoredProc

ClientDataSet/MyBase

"The ClientDataSet component ships with the Client/Server and Enterprise editions of Delphi and C++ Builder. This component, which can be used in place of other DataSet components, permits for the reading and writing of single user flat files. The ClientDataSet component relies on a 150K DLL named DBCLIENT.DLL, but does not make use of the BDE."

Database-specific solutions

If you have the choice of database and don't mind making your application database-specific, you can use some library that connects to the database directly (MySQL, SQLite, Interbase Express/IBExpress/IBX or FIBPlus/UIB/IBObject for Firebird, etc.)

If you're accessing Microsoft SQL Server or Access databases, you'll probably prefer to use ADO. If you're using Paradox or InterBase, then the BDE is probably still the best bet -- unless you've boarded the InterBase Express.
 
Generic client-to-database layers like the BDE, ODBC, dbExpress and ADO hide most of the capabilities of transactional database engines, flattening connectivity to a generic "lowest common denominator".
 
Powerful server databases like InterBase/Firebird and Oracle are made to conform to the behaviors of desktop databases like Paradox or dBase. It takes heavy layering of client and middleware driver code between the user and the database to accomplish this flattening, while disabling essential capabilities of the server databases' engines. Since everything in InterBase/Firebird happens inside transactions, this approach essentially kills most of the benefits of using client/server for networking mission-critical applications. IBO cuts right through all this and connects its data access objects directly to the application programming interface (API) of the InterBase/Firebird engine. From the start IBO freed itself from the restrictions of TDataset and its limiting, local database oriented memory model.
 
One of IBO's significant benefits is that its native data access architecture is built from TComponent up. This means you you can harness the full power of IBO without the TDataset architecture that Borland provides. What this means in terms of software investment is that you can use IBO with the standard version of Delphi - VERY cheap compared to the Professional and Enterprise versions.
 
The ZeosLib is a set of database components for MySQL, PostgreSQL, Interbase, Firebird, MS SQL, Sybase, Oracle and SQLite for Delphi, FreePascal/Lazarus, Kylix and C++ Builder."

MyBase

And if you only need a local database (ie. no connection over the network), and the amount of data is small, check out MyBase (ex-MIDAS). It only required midas.dll, and a ClientDataSet to handle data in RAM

MIDAS/DataSnap

"With MIDAS (Multi-Tier Distributed Application Services), your VCL-based client application receives data over a TCP/IP connection or through the use of sockets. The data is provided by an application server, which you also write using Delphi. While the application server does make use of the BDE, the client application does not. Client applications created using MIDAS are often referred to as thin clients, since they require less configuration and fewer files (specifically, no BDE)."

"MIDAS (DataSnap) is needed with DbExpress, at least if you want to present data in a GUI. MIIDAS is optional with IBX and not really needed with the ADO components. Think of DbExpress + MIDAS as the "new" BDE."

How does Delphi work with database engines?

  1. You build the UI with DB-aware components like DBGrid or DBNavigator that share a common datasource
  2. The datasource is a conduit to...
  3. a dataset, which contains a set of records from a database, read from either a single table or multiple tables through a SQL SELECT:
  4. Each type of dataset uses a different connection component to actually access the DB engine:
  5. Finally, the connection component connects to the actual database, either file- or server-based.

Data module = Data source + Dataset + Connection

Database components are globally available within your application. In other words, so long as your Database component appears on an auto-created form, or appears on the main form, it is available to all forms and data modules in the application, without the need for a corresponding uses clause statement.

Since DataSource components are used primarily for managing the interaction between data controls and DataSets, you rarely need to use a DataSource for data access that is entirely programmatic. In other words, if you have no user interface, you probably do not need a DataSource.

The simplest form of database doesn't use a database engine, and saves data in a file instead through the MyBase (ex-MIDAS) so that client datasets can save and read themselves to/from a disk; In this case, use the dataset's SaveToFile() and LoadFromFile() methods, or set the FileName property to make it easier.

There are three basic classes of datasets:

In addition, TDataSet has some descendants that fit into more than one category:

The ClientDataSet component, which can be used in place of other DataSet components, permits for the reading and writing of single user flat files. The ClientDataSet component relies on a 150K DLL named DBCLIENT.DLL, but does not make use of the BDE.

It is possible to use a specialized client dataset to connect to a dataset; This type of specialized client datasets is a composite component that includes another dataset internally to access the data and an internal provider component to package the data from the source dataset and to apply updates back to the database server. You might want to use a two-part dataset for the following reasons: A client dataset can work reliably with a cache instead of applying changes directly to the database; You can improve performance by running a client dataset on a client PC and a dataset on a server; datasets like dbExpress' are read-only; TClientDataSet can link to any source dataset, even those that don't provide a specialized client dataset.

A single connection component can be shared by multiple datasets, or each dataset can use its own connection. Each type of dataset connects to the database server using its own, TCustomConnection-derived type of connection component, which is designed to work with a single data access mechanism:

All database connection components except TIBDatabase let you execute SQL statements on the associated server by calling the Execute method. Although Execute can return a cursor when the statement is a SELECT statement, this use is not recommended. The preferred method for executing statements that return data is to use a dataset. The Execute method is very convenient for executing simple SQL statements that do not return any records. All database connection components maintain a list of all datasets that use them to connect to a database. A connection component uses this list, for example, to close all of the datasets when it closes the database connection.

Useful methods to retrieve metadata from the database server:

Datasets offer navigation and search methods like First, Last, Next, Prior, MoveBy, Bof, Eof, Bookmark, Locate, Lookup, Filter.

Here's how to have a dataset run an SQL query programmatically:

//The dataset must be closed when you specify or modify the SQL property.
MyQuery.Close;
MyQuery.SQL.Clear;
MyQuery.SQL.Add('SELECT CustNo, OrderNO, SaleDate');
MyQuery.SQL.Add(' FROM Orders');
MyQuery.SQL.Add('ORDER BY SaleDate');
MyQuery.Open;

Since MyQuery is a TStrings, any item can be access and changed:

MyQuery.SQL[2] := 'ORDER BY OrderNo';

You can also load an SQL query from file:

MyQuery.SQL.LoadFromFile('custquery.sql');

Here's how to build an SQL query by providing parameters at runtime:

SQLQuery1.ParamByName('Capital').AsString := Edit1.Text;
INSERT INTO Country (Capital) VALUES (:Capital)

Queries that don't return a result set should be run by calling ExecSQL:

CustomerQuery.ExecSQL;

If you are executing the query multiple times, it is a good idea to set the Prepared  property to True.

Here's to modify a record in a dataset:

with CustTable do begin
  Edit;
  FieldValues['CustNo'] := 1234;
  Post;
end;

Unlike most datasets, client datasets can also position the cursor at a specific record in the dataset by using the RecNo property. Ordinarily an application uses RecNo to determine the record number of the current record. Client datasets can, however, set RecNo to a particular record number to make that record the current one.

Persistent fields are the fields added to the dataset at design time using the field editor, saved in dfm file and loaded from the resource at runtime. Called persistent because they are not recreated everytime the dataset is closed and re opened.

To check

How to do this?

More information

Managing data with FireBird

http://www.destructor.de/firebird/1.5/embedded.htm

"Borland's Delphi doesn't seem to work with Firebird 1.5. I just get messages like "Connection to database refused."

The Windows client library in Firebird 1.5 and higher is named fbclient.dll and is located in Firebird's \bin directory. Anything Made in Borland expects a client library named gds32.dll located in the system path. You'll need to generate a special version of the Fb 1.5 Windows client library that is named gds32.dll and contains a version string recognised by Borland products. If you choose the "compatibility" option during the installation, this library will be generated for you and placed in the \bin directory, ready for you to copy over to your system directory.

If you didn't take the compatibility option during install, you can generate the special client yourself using the utility program instclient.exe (also in \bin). The doc for it is in \doc\ README.Win32LibraryInstallation.txt."

What package to get? http://www.firebirdsql.org/index.php?op=files or http://prdownloads.sourceforge.net/firebird/

Managing data with Firebird embedded

More information here.

Managing data with SQLite

More information here.

Other engines

Handling errors using exceptions

Debbuging tools and tips:

An exception is an alternative way for a function to report the outcome of its operation. Not all functions and packages support exceptions, though. Here's some pseudo-code:

If MyFunc() = False then begin
    ShowMessage('MyFunc failed');
    Exit;
end;

or

try
    MyFunc();
except
    ShowMessage('MyFunc failed');
end;

There are two kinds of exceptions: try..finally blocks, and try..except blocks. Typically, you use try..finally blocks to protect resources, and try..except blocks to handle exceptions. Try/finally are much more used than try/except, as the former is an easy way to avoid memory leaks by making sure you release any resource dynamically allocate, regardless of the outcome.

If you just want to run some code that could trigger an exception, use the following:

try
    //stuff that could trigger an exception
except
    //Handle exception
end;

If you don't want to handle an exception, but make sure to free a resource that you allocated before running the code likely to bomb, use this:

AllocateResource
try
    //stuff that could trigger an exception
finally
    //Free resource
end;

If you want both to handle an exception and perform some tasks even when things went ok, you'll have to run the following structure with a second try embedded (Delphi doesn't provide a single try/except/finally structure):

AllocateSomeResources;
try
    try
        //stuff that could trigger an exception
    finally
        //perform general actions, such as FreeAndNIL()
    end;
except
    //handle exception
    on E: Exception do begin
        MessageDlg(E.Message, mtWarning, [mbOK], 0);
    end;
end;

This could be layed out differently:

AllocateSomeResources;
try try
    //stuff that could trigger an exception
finally
    //perform general actions, such as FreeAndNIL()
end; except
    //handle exception
    on E: Exception do begin
        MessageDlg(E.Message, mtWarning, [mbOK], 0);
end;

You might wonder why a resource is allocated before instead of inside a try block. The reason is that, when we call a constructor, we are assured that either the call succeeds and we get a valid object, or the call fails and all resources are released. This is why we can place a constructor right before a try..finally block - if the constructor raises an exception, there will be nothing to free.

If you only want to catch an exception but actually have it handled elsewhere (eg. centralizing it), use the Raise() function:

Result := SomeResource.Create;
try
    Result.TrySomething;
except
    Result.Free;
    raise; //Let error bubble up and be handled elsewhere up there
end;

An alternative is to attempt to create an object, and use a Try/Finally to Free the object: In case the object couldn't be created in the first place, Delphi will jump to the nearest exception handler, and the Finally section is ignored entirely:

Strings1 := TStringList.Create;
try
    Strings1.Add('Hello, world!');
finally
    Strings1.Free;
end;

From Exception Handling for Fun and Profit (a.k.a. Exception Handling in Delphi) by Nick Hodges: "One of the main purposes of exception handling is to allow you to remove error-checking code altogether and to separate error handling code from the main logic of your application.

One way to do that is to centrally handle exceptions. TApplication has an event that allows you to do just that – the OnException event. You can use this event to deal with all exceptions of any type that aren't otherwise handled by your application. You can use this event to log your exceptions, or provide specific handling for specific types of exceptions.

With exception handling, you can write your code as if nothing ever goes wrong, and then wrap that code up with try…except blocks if you like to deal with any of the errors and problems that may occur. This enables your code to run more efficiently, as it isn’t constantly checking parameters and other data to make sure that it is in the proper form before doing anything with it."

"As noted above, you should never eat exceptions. What you should do instead is to trap only specific exceptions that might reasonably be expected to occur in your code.

As I mentioned above, I see code that eats exceptions added because the developer (or manager, or someone not thinking very clearly) never wants the user to see any errors. The way to deal with that is to trap the specific exception that the user is seeing. For instance:

try
  SomeCodeThatRaisesAnEConvertError;
except
  on E: EConvertError do begin
  // Deal with this specific exception here
  end;
end;

Furthermore, database exceptions (and some others, like COM errors) generally include an error code, and you may wish to trap only errors with a certain error code and allow others to surface.  You can do this as follows:

try
    SomeCodeThatRaisesAnEConvertError;
except
    on E: EIBError do begin
        if E.ErrorCode = iSomeCodeIWantToCatch then begin
            // Deal with this specific exception here
        end else begin
            raise; // re-raise the exception if it’s not the one I handle
        end;
    end;
end;

Bottom line: Trap exceptions as far down the class hierarchy as you can and only trap those exceptions that you are planning on handling.

If you are like most of us, when first learning to use exception handling, you are tending to use exception blocks far too much. In most cases you do *not* want to handle every possible exception at every possible place in your code. You *do* however, want to take advantage of finally blocks as often as you can to guarantee against memory and resource leaks.

Perhaps you should consider using Application.OnException to avoid the default dialog box showing. This way you won't have to catch the exceptions, but you can still avoid them being visible to the end user.

Resources

Components

Note

Tabs

As an alternative to showing multiple forms, you can use a tab control and stick a group of controls in each page of the tab.

Additional > TTabSet

Win32 > TTabControl and TPageControl

From Cantu's "Mastering Delphi7":

PageControl.Page stores a list of TabSheet objects.

Every time you need multiple pages that all have the same type of content, instead of replicating the controls in each page, you can use a TabControl and change its contents when a new tab is selected.

TTabSet vs. TTabControl vs. TPageCtrl/TTabSheet?

Building reports

A report is a form with fields that you fill with data and send to the printer, possibly providing a preview so that the user can see what it'll look like before actually printing the page.

Report generators let you build forms in two ways: Through a designer at design-time (ie. like drawing forms in the Delphi IDE), or through code at run-time.

FastReports 4 VCL

the developers manual as to how to create custom objets and function libs for fr.

If you don't have the installer, here's how to install FastReport 4 manually:

  1. Unzip the package
  2. Add the following directories to the Delphi IDE:

    FastQB
    FastScript
    ExportPack
    Source
    Source\ADO
    Source\BDE
    Source\DBX
     
  3. Compile all the *.bdsproj file in the different directories
  4. In addition, all the project files that start with "dcl" are design-time components, so they also need to be installed (Right-click on the project, choose Install, then close the project)

    Note: The Source\FIB\dclfrxFIB11.bdsproj requires the commercial FIBPlus component. Compiling this project will fail otherwise

Several demo projects in... \Demo.

The Text object can also include tags that will be converted at run-time: "Hello, World! Today is [DATE]."

A Band is used to place a group of objects at a specific location in a page. Use File > New Report to start with a three-band page. Bands are useful to add recurrent occurences such as headers and footers.

Reports can be scripted (Pascal, C++, Basic, JScript), so you don't have to do this from the application.

Charts can be added through the TfrxChartObject component based on the TeeChart library which comes with Delphi.

FastReport provides extensive support for fetching data from databases, using ADO, BDE, IBX, etc.

If you need, you can add dialog boxes in a report (File > New Dialog), so you can eg. display some warning before printing a report, or prompting the user to provide some data through an inputbox.

Here's how to build a basic, one-page report at design-time to show a barcode, fill it with data at run-time, display a preview version, and let the user send it to the printer:

  1. Create a new VCL project
  2. Open the FastReport tab, and drop a TfrxReport control onto Form1
  3. Drop a TfrxBarcode as well
  4. Double-click the TfrxReport to start the Designer
  5. In the palette on the left side, add a Text object (for the description) and a Barcode object
  6. File > Save to save the design-time file. By default, the report will be saved in the form's DFM file. Close the Designer
  7. Back in Delphi, add a push button, and add the following code to fill variables with data, display the Preview dialog to let the user check that it looks OK and then send the job to the printer:

    frxReport1.ShowReport(); 

ReportBuilder

QuickReports

Rave Reports

Ships with Delphi, but maybe it's a limited version compared to the one available from www.nevrona.com. As of August 2009, the site is not well maintained (nothing in News, empty page when clicking on Features, etc.).

A Rave project than hold more than one report, and each report can have one or more pages. Leonel Togniolli wrote a four-part series of articles as an Introduction to Rave Reports. The reports can either be an external file, or embedded in the EXE.

Here's how to create a report using Rave 7.5.2 that ships with Delphi2007, and allow the user to push a button to fill the report with data and send the page to the printer:

  1. Create a new VCL project
  2. From the Rave tab, drop a TRvProject in the form. This is the connection between your application and the the report that we will produce below
  3. (optional) You can add a TRvSystem and link it to the RvProject control through its Engine property. RvSystem is responsible for the general configuration of the reports (which printer to use, the margins, etc.)
  4. Double click the RvProject control
  5. In the Designer window, add a text widget
  6. Hit F9 to check that it works
  7. Save the project file and close the Designer
  8. Back in Delphi, change RvProject.ProjectFile property to point to this Rave project file
  9. Add a pushbutton on the form to call RvProject1.Execute()

Here's how to add parameters to the project/report/page and set them from the Delphi application:

  1. Open the Rave Designer application
  2. Select the report in the treelist on the right
  3. Open the Parameters item
  4. Add "Name" as a parameter, and close
  5. From the Report tab, add a DataText control, change its DataField property (Project Parameters) to link it to the Name variable that we just created. Click on the Insert Parameter button, and OK
  6. Close the Designer, and go back to the Delphi IDE
  7. Modify the ButtonClick event thusly:

    RvProject1.Open;
    RvProject1.SelectReport('ParametrizedReport',False);
    RvProject1.SetParam('Name','Leonel');
    RvProject1.Execute;
    RvProject1.Close;

Post-Initialize Variables are those, like number of pages, that are only available after a report has been pre-processed and is ready to be printed.

It's obviously also possible to have the reporting tool connect to a database, and fill variables with this data.

Elements common to multiple pages or reports can be put in a Global page.

A section, a.k.a. Mirror, is a collection of components, eg. a header with a title, page number, date and time of print, etc.

Rave also supports conditional printing.

Printing barcodes on labels

Here's the goal. The barcode will be read by an ANL-810 scanner, which supports multiple coding standards including Code 39, Code 32, CIP39, Code Bar (CLSI), EAN-13 UPC-A, EAN-8, Code 128 (EAN 128), etc.

Note that Code 39 doesn't support lower case letters and many other characters. Code 39 is a good barcode to start with, because it's easy and doesn't require any checksum calculations. If you need characters that can't be provided by Code 39, try Code 128 B. That gives you the entire printable ASCII set. You'll need to generate a checksum, and you'll need to map the codes to characters if you're using a font - it might be easier to generate as pure graphics. That's why the ActiveX controls are so popular.

"I suggest Fast Report the best Report tool I have used. I have used QuickReport, Fortes Report, Report Builder and Rave before Fast Report."

"I use Fast Reports to print my barcodes. it has built in barcode support which makes it pretty easy to use"

"ReportBuilder Pro is a very good report generator for adding printing capabilities to your program."

Free 3of9 Font

http://www.barcodesinc.com/free-barcode-font/

Online Barcode Generator

http://www.barcode-soft.com

TBarcode

TurboPower SysTools

Barcodes for Delphi

Han-Soft Barcode VCL

Planner

TMS Software DBPlanner

http://www.tmssoftware.com/site/dbplanner.asp

DevExpress ExScheduler

http://www.devexpress.com/Downloads/VCL/ExScheduler/

ShorterPath Planners

http://www.shorterpath.com/products/planners/

InnovaSoftware Calendar Works

WYSIWYG edit widget

Here are some components you can use if you need to add a WYSIWYG editor in a Delphi application. Some come as VCLs, others as C-DLLs or COM-DLLs. Some support HTML, others use RTF (ie. you can embed pictures in the file, but those controls typically don't support Hx tags, etc.). Note that with the introduction of IE 5.5, Microsoft's DHTMLEdit component has been superseded by the MSHTML Editor:

HTML Viewers

Those only display HTML:

Here's how to display some HTML in a TRichView widget:

  1. First, install the designtime- and runtime- packages, and add a TRichView and a TRVStyle widgets to a form
  2. Next, add the following code

      RichView1.Style := RVStyle1;
      RichView1.AddNL('Hello World!', 0, 0);
      RichView1.Format;

The way TRichView works, applying a different style to a string requires first making the change to its linked TRVStyle widget via its RVStyle1.ParaStyles property, and then send a string to be formatted.

HTML Cleaners

Outlook Bar

To build the familiar vertical bar in MS Outlook:

Grid

As of April 2005, recommended grid widgets are GridView, Profgrid, TMS TAdvStringGrid, Virtual Treeview, SMDBGrid, and ExpressSpreadSheet if you have the dinero. Here are some solutions I found of VCL grid widgets under active development, DB- and non-DB aware:

Here's a possible check-list:

As a reference, here's the size of an EXE built with Delphi 7 Enterprise to contain just a grid (make sure you clean up the Uses line in the PAS file when replacing one grid with another...):

Borland's TValueListEditor

This is a two-column grid that you can use to display/change "key=value" tuples:

for i := 0 to ASQLite3Query1.FieldCount -1 do begin
    FieldName := ASQLite3Query1.Fields[i].FieldName;
    KeyVal := Format('%s=%s',[FieldName,ASQLite3Query1.FieldByName(FieldName).AsString]);
    ValueListEditor1.Strings.Add(KeyVal);
end;

Scalabium SMDBGrid

Here's how to add and work with SMDBGrid:

  1. Launch Delphi, and open the DPK file, eg. SOURCES\SMCmpntD7.dpk. If you already had an older version installed, the Install button is disabled
  2. Add this new directory to Delphi' Library path
  3. Once installed, click in the palette on the SMComponents tab, and add an SMDBGrid widget to a form

[Fatal Error] Unit1.pas(7): File not found: 'Calendar.dcu'. Checked that I had the "VCL Source" installed.

No forum for support?

Berg GridView

Moved here.

Kgrid

X-Files X-DBGrid

http://www.x-files.pl

TMS Software

To use TMS' TAdvStringGrid, it's better to start with Borland's TStringGrid documentation, since TAdvStringGrid is based on it.

If you need a non-DB-aware editable grid, use TAdvColumnGrid instead: It has all the features of TAdvStringGrid combined with a flexible design-time and run-time management of cell properties, inplace editors, cell print properties, sort style and formatting.

Here are a few actions that you can perform with this control:

procedure TForm1.FormCreate(Sender: TObject);
var
  index : Integer;
begin
  With AdvColumnGrid1 do begin
    Look := glSoft;
 
    //FixedRows := 0;
    FixedCols := 0;
    ColCount := 3;
    //RowCount := 4;
 
    Columns[0].Name := 'key';
    Columns[0].Header := 'mykey';
    Columns[1].Name := 'value';
    Columns[1].Header := 'myvalue';
 
    //Make all columns read-only, except the one called 'value'
    for index := 0 to ColCount - 1 do begin
      Columns[index].ReadOnly := not (Columns[index].Name = 'value');
    end;
 
    //Have right-most column fill all available space until scrollbar
    ColumnSize.Stretch := True;
 
    //Can't use goRowSelect and still let user edit cells
    //Options := Options + [goRowSelect,goEditing];
    Options := Options + [goEditing];
    //As an alternative to goRowSelect and still let user edit cells,
    //change background color on currently-selected row
    
    //Let user resize, and move columns
    Options := Options + [goColSizing,goColMoving];
 
    //Here's how to refer to columns by their names
    Cells[ColumnByName['key'].Index,1] := 'test';
  end;
 
end;
 
//Simulate row selecting by changing font and background colors
procedure TForm1.AdvColumnGrid1RowChanging(Sender: TObject; OldRow,
  NewRow: Integer; var Allow: Boolean);
var
  index : Integer;
begin
  with AdvColumnGrid1 do begin
    RowColor[OldRow] := clWhite;
    RowFontColor[OldRow] := clBlack;
 
    RowColor[NewRow] := clHighlight;
    RowFontColor[NewRow] := clWhite;
  end;
end;
 
//When user edits cell, set current row's font + background colors back to normal
procedure TForm1.AdvColumnGrid1DblClickCell(Sender: TObject; ARow,
  ACol: Integer);
begin
  with AdvColumnGrid1 do begin
    RowColor[ARow] := clWhite;
    RowFontColor[ARow] := clBlack;
  end;
end;
 
//Triggered when users edits a cell
procedure TForm1.AdvColumnGrid1GetEditText(Sender: TObject; ACol,ARow: Integer; var Value: string);
var
  today : TDateTime;
begin
  today := Time;
  Label1.Caption := IntToStr(MyCounter);
  Inc(MyCounter);
end;
//Triggered when user is done editing a cell
procedure TForm1.AdvColumnGrid1CellValidate(Sender: TObject; ACol, ARow: Integer; var Value: string; var Valid: Boolean);
begin
  ShowMessage('AdvColumnGrid1CellValidate: ' + Value);
end;

Here's a simpler way to change the background color of every other row to cream white:

procedure TForm1.AdvColumnGrid1GetCellColor(Sender: TObject; ARow, ACol: Integer; AState: TGridDrawState; ABrush: TBrush; AFont: TFont);
begin
  //Ignore Row[0], ie. header
  if ARow > 0 then begin
    if (ARow Mod 2 = 0) then begin
      ABrush.Color := clCream;
      AFont.Color := clBlack;
    end;
  end;
end;

Note that a grid cannot have just a header, ie. fixed, grey row; It must have at least one non-header row, ie. RowCount > FixedRows:

With AdvColumnGrid1 do begin
    ColCount := 1;
    FixedCols := 0;
 
    //Very first row is fixed to show as header
    FixedRows := 1;
    //Must have at least one non-header row
    RowCount := 2;
    //Each column can have a caption and a name
    Columns[0].Header := 'Col 1';
    Columns[0].Name := 'sql_col1';
    //Useful when looping through StringList to create columns
    Columns[0].ReadOnly := not (Columns[0].Header = 'Col 1');
end;

Here's how to display the content of a column in the currently-selected row:

procedure TForm1.AdvColumnGrid1DblClick(Sender: TObject);
var
  MyID : String;
begin
  With AdvColumnGrid1 do begin
    MyID := Cells[ColumnByName['article_id'].Index,Row];
  end;
  ShowMessage(MyID);
end;

Note: Unlike TAdvColumnGrid.GetEditText, TAdvColumnGrid.CanEditCell is called twice when clicking on a cell (but once when moving to a cell through the keyboard, and once again when switching to edit mode through eg. F2). Here's how to make a column read-only but allow editing for a specific cell depending on the value of another column in this row:

CanEdit

Here's how to build a two-column grid to display a key=value interface, with the very first column hidden so as to keep a table's SQL column names alongside their user-friendly equivalent:

With AdvColumnGrid1 do begin
    ColCount := 3;
    
    //Hidden column
    Columns[0].Header := 'SQL';
    Columns[0].Name := 'article_id';
 
    Columns[1].Header := 'Key';
    Columns[1].Name := 'key';
    Columns[1].ReadOnly := True;
    Columns[1].Color := clMedGray;
 
    Columns[2].Header := 'Value';
    Columns[2].Name := 'value';
 
    //Hide "SQL column"
    HideColumn(0);
 
    //Make first row look like a header
    FixedRows := 1;
    RowCount := 2;
 
    Cells[ColumnByName['key'].Index,1] := 'Second_key';
    Cells[ColumnByName['value'].Index,1] := 'Some dummy value2';
 
    Look := glStandard;
    ColumnSize.Stretch := True;
    Options := Options + [goEditing];
    AutoSizeColumns(True);
end;

Here's how to add a TAdvColumnGridcontrol to a form, and fill it with a SELECT from a database:

DevExpress

ExpressQuantumGrid

Here's how to install DevExpress QuantumGrid Suite 6.38 in D2007:

  1. Add the following paths to the IDE's Library Paths:

    ExpressLibrary\Packages
    ExpressLibrary\Sources
    ExpressQuantumGrid 6\Packages
    ExpressQuantumGrid 6\Sources
    ExpressDataController\Packages
    ExpressDataController\Sources
    ExpressEditors Library 5\Packages
    ExpressEditors Library 5\Sources
    ExpressExport Library\Packages
    ExpressExport Library\Sources
    ExpressGDI+ Library\Packages
    ExpressGDI+ Library\Sources
    ExpressPageControl 2\Packages
    ExpressPageControl 2\Sources
    XP Theme Manager\Packages
    XP Theme Manager\Sources
     
  2. Compile ExportLibrary\cxLibraryD11.dpk, and compile/instal dclcxLibraryD11.dpk
  3. Compile QG\cxGridD11.dpk and compile/install dclcxGridD11.dpk
  4. Compile DC\cxDataD11.dpk, cxADOAdaptersD11.dpk, cxBDEAdaptersD11.dpk, cxIBXAdaptersD11.dpk
  5. Compile cxEditorsD11.dpk, compile/install dclcxEditorsD11.dpk, compile cxExtEditorsD11.dpk, compile/install dclcxExtEditorsD11.dpk
  6. compile cxExportD11.dpk
  7. compile dxGDIPlusD11.dpk
  8. compile cxPageControlD11.dpk, compile/install dclcxPageControlD11.dpk
  9. compile dxThemeD11.dpk
ExpressSpreadSheet

ObjectSight TopGrid

DbAltGrid

Virtual TreeView

Moved here.

ProfGrid

TStringGrid

This is the standard grid object that comes with Delphi7, and only has basic features. If you want a widget that resizes itself automatically to adapt to the width of the items and offers sorting by clicking on a column header, you'll have to program this yourself.

TListView

This grid also comes with Delphi, can be used in combination with TTreeList or by itself, and looks more modern that TStringGrid. It doesn't natively support sorting by clicking on an column header, but this can be implemented easily.

Extended StringGrid

TKStringGrid

JVCL

ABF

VCL
abcComponents

TjanGrid

ElTree Lite 3.20

TXDBGrid

TExDBGrid

RXLib

Torry Grids

A bunch of grids at Torry, but most too basic and deadware

Woll2Woll Infopower

List of older components

http://www.kobira.co.jp/sakura/d_table.htm

TCRGrid enhanced VCL data-aware grid control

TfzGrid

FlyTreeView

TxDbGrid

Task Pane

This is the alternative to the Outlook bar introduced with XP. At least five widgets are available: (RIP) TEasyTaskBand, Raize TRzGroupBar, TMS TAdvPanelGroup (also available in the TMS Component Pack), DevExpress ExpressNavbar, ??? in the JVCL, LMD BarPack, and (RIP) TBX (add-on package to the Toolbar 2000 package).

Here's how to work with MustangPeak's TEasyTaskBand:

type
    EasyTaskBand1: TEasyTaskBand;
    ImageList1: TImageList; //Big icons for groups
    ImageList2: TImageList; //Small icons for items in groups
[...]
var
    Group: TEasyCollectionItem;
    Item: TEasyCollectionItem;
    Group: TEasyGroup;
    Item: TEasyItem;
begin
    EasyTaskBand1.BeginUpdate();
    Group := EasyTaskBand1.Groups.Add;
    Group.Caption := 'Group 1';
    Group.ImageIndex := Random(ImageList1.Count);
    Item := Group.Items.Add();
    Item.Caption := 'Item: ' + IntToStr(j);
    Item.ImageIndex := j mod ImageListSmall.Count;
    Item.Captions[1] := 'Detail 1';
    Item.Captions[2] := 'Detail 2';
 
    Item := EasyTaskBand1.Groups[0].Items.Add;
    Item.Caption := 'Item: ' + IntToStr(Item.Index);
    Item.ImageIndex := 0;
 
    Item := TEasyGroupStored(Group).Items.Add;
    Item := LV.Items.Add;
 
    EasyTaskBand1.EndUpdate();
    EasyTaskBand1.Groups.Clear
    EasyTaskBand1.Groups[0].Bold := CheckBoxSpecialGroup.Checked

If you want a task pane to resize automatically if the user changes the form's size (eg. going from maximized to some smaller, custom size), set the pane's Align property from its default alNone to alLeft.

Internet

Here's how to fetch a web page and display its HTML source in a memo using ICS' HTTP client.

Here are some well-known components that support Internet protocols:

To read

Creating objects at runtime

If using "nil" as the owner, you must call the Free() method or you'll get a memory leak.

You don't have to use a variable to hold the pointer to the instance (source):

with TTimer.Create(Self) do begin
   Interval := 1000;
   Enabled := False;
   OnTimer := MyTimerEventHandler;
end;
//Do NOT call Free with try/finally!

or

with TTable.Create(nil) do
try
   DataBaseName := 'MyAlias';
   TableName := 'MyTable';
   Open;
   Edit;
   FieldByName('Busy').AsBoolean := True;
   Post;
finally
   Free; //If using variables, you can call FreeAndNil() instead
end;

... but it's recommended to use a variable, so you can refer to it later:

FTimer := TTimer.Create(Self) ;
 
if not Assigned(FTimer) then do begin
    ShowMessage('Not assigned');
    Exit;
end;
 
with FTimer do begin
   Interval := 1000;
   Enabled := False;
   OnTimer := MyInternalTimerEventHandler;
end;
FreeAndNil(FTimer);

Alternatively:

FTimer := TTimer.Create(Self) ;
try
    with FTimer do begin
       Interval := 1000;
       Enabled := False;
       OnTimer := MyInternalTimerEventHandler;
    end;
finally
    //Since Delphi doesn't provide try/expect/finally, here's a way to check for errors
    if not Assigned(FTimer) then do begin
        ShowMessage('Failed creating Timer');
    end else begin;
        FreeAndNil(FTimer);
    end;
end;

Resources

Displaying different sets of objects in a form

If you'd rather not use several forms to show sets of objects, two alternatives are available: Using a TPageControl, and using frames.

TPageControl

Use a TPageControl to host the different pages, hide them all, and only display the desired page when the user selects the item in a menu.

Frames

Create frames, and insert the desired frame in the main form at runtime

Resources

Displaying a lot of fields

If your application connects to a SQL server, it will have to display and handle a lot o fields that users can edit and save. Here are ideas proposed by experienced developers:

TabControl vs. PageControl? "Use TTabControl to add a control with multiple tab settings to a form. Unlike a page control, TTabControl is not made up of several pages that contain different controls. Instead, TTabControl is a single object. When the current tab changes, the tab control must directly update its contents to reflect the change in an OnChange event handler. (CLX?) TTabSheet is an individual page in a TPageControl object.

Use TPageControl to create a multiple page dialog or tabbed notebook. TPageControl displays multiple overlapping pages that are TTabSheet objects. The user selects a page by clicking the page’s tab that appears at the top of the control. To add a new page to a TPageControl object at design time, right-click the TPageControl object and choose New Page.

To create a tabbed control that uses only a single body portion (page), use TTabControl instead."

Microsoft Inductive User Interface Guidelines

Delphi.Net

To speed it up:

  1. Register with Borland, and download hotfixes
  2. Install DelphiSpeedup
  3. Make those changes
  4. "The installation should have created a shortcut named "Delphi for Microsoft Win32" in its program menu entry. Use that to start BDS with only the Win32 Delphi personality loaded. That will already speed up the load time. If you have not done so yet install the update 2 you can download from the registered users site. The BDS Welcome page has a link to that on the lower left."
  5. "You can disable component packs you do not need using the Components->Install packages dialog, just uncheck the design-time packages you do not need and don't forget to check the "Default" checkbox on the lower left of the dialog before you OK it."
  6. "You can even create a custom installation to exclude things you don't need. See http://homepages.borland.com/medington/DelphiStartupTimes.htm There are a number of unofficial hotfixes available as well that replace some of the standard IDE packages. They were originally posted on blogs by Borland people (e.g. http://blogs.borland.com/abauer ), but I think the registered users site lists them as well now."

Glossary

BDE

Borland Database Engine for database access

BPL

"Borland Package Library"; Delphi-specific, enhanced DLL

CLX

Borland CLX™ (Component Library for Cross-platform) library, which encapsulates the Qt widget set for Windows and Linux.

DataSnap

ex-MIDAS; Middleware

dbExpress and ClientDataSet

To create database apps

DCP

"Delphi Compiled Package"; Contains headers and symbols when compiling a DPK. Must be provided with a BPL for design-time packages.

DCU

Unit in compiled format. All DCUs are combined into a single EXE, with the possible addition of VCLs if you prefer that components be compiled into the EXE instead of as DLLs.

DFM

A file describing a form, its properties, and its components

DPC

"Delphi Package Collection" = bunch of BPLs in one file?

DPK

Delphi package project file

DPR

Delphi project file

ECO

ECO is the .Net version of Bold which was already available in Delphi 7. ECO lets you build a .Net application from an Object model, regardless of whether the persistent layer is object or relational.

Indy

To write socked-based apps

InterBase

Client/server RDBMS, still available from Borland as a commercial tool, but also available as open-source under the name of Firebird

IntraWeb

To create visual web applications (?)

Model Maker

To create UML class diagrams and generate code. Delphi 8 introduces Together, which is also a CASE UML tool and was already available in other Borland products like JBuilder or C++BuilderX.

PAS

Source file in Pascal

RAVE

To generate reports

Unit

Program module. In a Delphi application, every form has a corresponding unit behind it.

VCL

Visual Component Library (VCL)

RTL

Run-time library; Large collection of functions

Q&A

Add to read the selected item in a ComboBox?

ShowMessage(ComboBox1.Text);

Child forms: MDI or frame or pagecontrol?

If you need to show different sets of controls, you can do this either through MDI child windows (the main form being the MDI parent), stand-alone frames, or frames displayed in a pagecontrol (tab widget).

Unlike regular forms, MDI child windows can not be shown modal (so you can't just use a simple try/finally to remove the object from memory with Free(), and you'll have to have the MDI child window call some routine in its parent window to have it be removed from RAM), and they flicker when displayed. A frame doesn't show flickers when it is displayed. Both MDI child windows and frames require calling their parent to be removed from RAM.

How to add a routine to the list in the class?

After writing the routine, you can have it added to the form's class by using the keyboard combination CTRL-SHIFT-C

Get a list of methods, properties, and events provided by an object?

Either use Delphi's Runtime Type Information (RTTI), or (no: Doesn't display anything) GExpert's Class Browser.

How to install GExperts?

How to upgrade CnWizards?

Close the IDE and run the installer

TControl(Sender) vs. Sender as TControl?

(From embarcadero.public.delphi.language.delphi.general):

How can a runtime frame notify its parent form?

In the frame:

type
  TFrame3 = class(TFrame)
  private
    FOnDone: TNotifyEvent;
  public
    property OnDone: TNotifyEvent read FOnDone write FOnDone;
  end;
 
procedure TFrame3.Button2Click(Sender: TObject);
begin
  if Assigned(FOnDone) then begin
    FOnDone(Self);
  end;
end;

In the form:

interface
 
const
  APPWM_FREE_FRAME = WM_APP + 100;
 
type
  TForm1 = class(TForm)
  private
    procedure FrameIsDone(Sender: TObject);
    procedure AppWmFreeFrame(var Message: TMessage); message APPWM_FREE_FRAME;
  end;
 
procedure TForm1.AppWmFreeFrame(var Message: TMessage);
begin
    TFrame(Message.LParam).Free;
end;
 
procedure TForm1.FrameIsDone(Sender: TObject);
begin
  if Sender is TFrame3 then begin
    PostMessage(Handle, APPWM_FREE_FRAME, 0, Integer(Sender));
  end;
end;
 
procedure TForm1.Button1Click(Sender: TObject);
var
  Frame3 : TFrame3;
begin
  Frame3 := TFrame3.Create(nil);
  Frame3.Align := alClient;
  Frame3.Parent := Self;
  Frame3.OnDone := FrameIsDone;
  Frame3.Visible := True;
end;

ie. calling TFrame1.Done changes the frame's OnDone property, which triggers the frame's FOnDone custom event which is linked to the form's FrameIsDone procedure, which calls AppWmFreeFrame to call PostMessage and actually unload the frame from memory.

How to close a dynamically-created form?

In the calling form:

if Form2 = nil then begin
    Form2 := TForm2.Create(nil);
    Form2.Show;
end;

In the dynamically-created form:

procedure TForm4.Button2Click(Sender: TObject);
begin
  Close;
end;
procedure TForm4.FormClose(Sender: TObject; var Action: TCloseAction);
begin
  Action := caFree;
  Form2 := nil;
end;

How to check that a datamodule is loaded?

  1. Project > Options, and make sure the datamodule is loaded first before any form is loaded
  2. In a form, use the following code to double-check:
    if Assigned(DataModule3) then begin
        ShowMessage('assigned');
    end else begin
        ShowMessage('not assigned');
    end;

How to use ExeName in a datamodule?

If  you need to get the application's ExeName in a datamodule, either add "Forms" to the Use clause, or change Application.ExeName to ParamStr(0).

Can the IDE show the matching end for a given begin?

How to support Far-East languages in Delphi 7

Why use Delphi over VB?

Why use Delphi over Borland C++?

The reason I mention Borland C++ over MS VC++ is that I read that the former has a tool that lets you build GUI screens graphically, while the latter still requires you to write the whole thing in code, so cannot be reasonably compared to Delphi or VB.

Personally, I find C/C++ a pain to use, because the language itself requires your paying attention to details that are just a waste of time most of the time when developing client-side applications, and keep you from concentrating on the problem the application is trying to solve. Considering you can build tight, dependency-free code with Delphi, what's the point of wasting time with a lower-level language that was originally just meant for system development back in 1970?

Why upgrade from D7?

IDE 

Form Designer

Code Editor:

Debugger

dbExpress

VCL

Delphi Language Enhancements:

More information on changes since Delphi 7

Why install IDE add-on's GExperts and cnWizard?

cnWizards shows a list of bookmarks (CTRL-SHIFT-b) and a list of routines (CTRL-d).

GExperts offers a Class Browser to see the list of methods, properties, and events provided by an object.

Why use Delphi vs. alternatives to write .Net apps?

Since the main selling point was the productivity of VB but the speed/compactness of VC++, I don't see the added-value of using Delphi 2005 over VB.Net, unless you're more familiar with Delphi and would rather use the same language to work with .Net.

After moving routines into Unit2, the project stops compiling

Make sure Unit2 is referenced in Unit1's Implementation through "Uses Unit2", and that all exported routines in Unit2 are declared in Unit2's Interface section.

How can I change the application's icon?

Project Options

How to change the default application icon?

Why does my local array start at 0 instead of 1?

An array created in a routine (procedure or function), even if its size is statically defined, is considered an "open array", and thus, starts at 0:

procedure Check(var ReturnArray: Array of String);
var
  Index : Integer;
begin
  // Says 1!
  ShowMessage(IntToStr(High(ReturnArray)));
end;
 
procedure TForm1.Button1Click(Sender: TObject);
var
  ReturnArray : Array[1..2] of String;
begin
  //Says 2, as expected
  ShowMessage(IntToStr(High(ReturnArray)));
 
  Check(ReturnArray);
end;

If you want the array to start at something else than 0, define the array as a new type:

type
  TMyArray = Array[1..2] of String;
  TForm1 = class(TForm)
  ...
procedure Check(var ReturnArray: TMyArray);
var
  Index : Integer;
begin
  ShowMessage(IntToStr(High(ReturnArray)));
end;
 
procedure TForm1.Button1Click(Sender: TObject);
var
  ReturnArray : TMyArray;
begin
  ShowMessage(IntToStr(High(ReturnArray)));
 
  Check(ReturnArray);
end;

How to have a listbox scroll down programmatically?

How do I use regexes in Delphi?

TPerlRegex

To install this RegEx engine for Delphi, open, compile and install PerlRegExD7.dpk, which creates PerlRegExD7.bpl, add its directory to the Library path, and add a TPerlRegEx control to the project's form.

Here's how to extract a single bit in a text:

PerlRegEx1.RegEx := '<title>(.+?)</title>';
PerlRegEx1.Options := [preCaseLess];
PerlRegEx1.Subject := 'test <title>bla</title> test';
If PerlRegEx1.Match then begin
    ShowMessage(PerlRegEx1.SubExpressions[1])
end else begin
    ShowMessage('Not found')
end;

Next, here's how to look for a pattern, and extract bits if found:

var
    RegEx : TPerlRegEx;
    Stuff : TStringList;
begin
    RegEx := TPerlRegEx.Create(nil);
    Stuff := TStringList.Create;
    Try
        RegEx.RegEx := 'my pattern';
        RegEx.Options := [preCaseLess];
        RegEx.Subject := 'this is the text to search for my pattern';
        
        If RegEx.Match then begin
            repeat
                for i := 1 to regex.SubExpressionCount do begin
                    Stuff.Add(regex.SubExpressions[i]);
                    Application.ProcessMessages;
                end;
            until not RegEx.MatchAgain;
 
            For I := 0 to Stuff.Count - 1 do begin
                Memo1.Lines.Add(Stuff[I]);
            end;
 
        end else begin
            ShowMessage('Not found');
        end;
 
    Finally
        RegEx.Free;
        Stuff.Free;
    End;
End;

Here's how to replace a pattern with something else:

RegEx := TPerlRegEx.Create(nil);
try
    RegEx.Subject := LoadFile('myfile.txt');
    RegEx.RegEx := 'HERE';
    RegEx.Replacement := 'THERE';
    If RegEx.Match then begin
        RegEx.Replace;
        ShowMessage(RegEx.Subject);
    end;
finally
    RegEx.Free;
end;

TRegExpr

Although TRegExp is much slower than TPerlRegEx on more complex operations, it's OK for light searches. Here's how to extract tokens from a text file using TRegExpr:

MyStuff := '<body>My stuff</body>';
 
with TRegExpr.Create do
    try
        //Make it case-insensitive
        ModifierI := True;
        
        Expression := '<body.*>(.*?)</body>';
        if Exec (MyStuff) then
            ShowMessage(Match[1]);
 
    finally
        Free;
end;

Here's how to extract several tokens, and put them in an array:

var
    Tokens : TStringList;
    MyRegex : TRegExpr;
 
begin
    MyRegex := TRegExpr.Create;
    Tokens := TStringList.Create;
    try
        MyRegex.ModifierI := True;
        MyRegex.Expression := 'some stuf (\d+) some other stuff';
        if MyRegex.Exec (Response) then begin
            REPEAT
                Tokens.Add (MyRegex.Match[1])
            UNTIL not MyRegex.ExecNext;
 
            Memo1.Clear;
            for I := 0 to Tokens.Count-1 do begin
                Memo1.Lines.Add(Tokens[I]);
            end;
 
        end else begin
            Memo1.Text := 'Pattern Not Found';
        end;
    finally
        MyRegex.Free;
        Tokens.Free;
    end;

And here's how to look for patterns, and replace them with something else:

ShowMessage(ReplaceRegExpr ('World','Hello, World!', 'Earth'));

You can also use references:

MyStuff := 'The number 123 here';
MyStuff := ReplaceRegExpr ('The number (\d+) here',MyStuff, 'Rewritten as $1', True);
ShowMessage(MyStuff);

Can I arrange the IDE to get a similar layout to VB's IDE?

You can combine the Object Inspector and Object TreeView windows through drag and drop,and dock them to the text editor with further drag and drop. Then, to tell Delphi to keep this layout, hit View > Desktops > Save Desktop, and give a name to this new layout.

Can I use Delphi without VCL?

You can write programs using just the Object Pascal, a.k.a. Delphi, language and make direct calls to the Windows API so as to builder smaller programs. Read Programming In A Subset Of Delphi, and DelphiZeus - Developing Delphi programs in Windows API without the Forms unit for more info.

How to get an MDI child form to use the whole client area?

procedure TForm1.RzGroup1Items0Click(Sender: TObject);
var
  Form2 : TForm2;
begin
  Form2 := TForm2.Create(Application);
  //BAD Form2.Align := alClient;
  Form2.Align :=
end;

How to close a child MDI form?

procedure TForm2.FormClose(Sender: TObject; var Action: TCloseAction);
begin
  Action := caFree;
end;

GPF when showing a second form

First, it looks like it's not enough for the second form to be part of the project: It must also be listed in the Uses section of the first form (ie. Uses Unit2), along with the var section of its interface (var Form2: TForm2;), before being called with this kind of code:

begin
  Form2 := TForm2.Create(Application);
  ShowMessage(Form2.Name);
  Form2.Show;
end;

I messed up Delphi with an update, and get errors at start-up!

I had an issue with the Rave part after running the 7.1 update. Here's how to restore Delphi:

  1. Exit the IDE
  2. Back up your source files
  3. Run D7RegClean.exe from your delphi BIN directory
  4. Uninstall delphi
  5. Reboot
  6. Reinstall.

I don't know if it hurts, but I also deleted Rave50CLXBE70.bpl and Rave50VCLBE70.bpl from \SYSTEM32.

Why use a package vs. a DLL?

(From "Delphi in a nutshell") A package has the extension .bpl ("Borland Package Library"), and avoid the problem of DLLs, namely, managing memory and class identities.

In the Project menu, what's the diff between Compile and Build?

Compiled = turn each PAS file into object code (DCU?), while Build = link all the compiled units into an EXE?

I can't compile my first program!

You must first save the .PAS file and the .DPR project file for the Project | Build Project to generate the EXE.

Can I compile DLLs and OCXs inside a big EXE?

From Greg Lorriman in comp.lang.pascal.delphi.misc (1999/10/03)

"The ocx's are NOT compiled into a delphi app. In this regard delphi has the same relationship to ocx's as VB. But a delphi app is much less likely to use ocx's than a VB app. I've never used one (except experimentally). [...]
 
So long as the components are native to Delphi then they can be compiled into the executable. By default the rest of the support code (which comes as runtime dll's in VB) is also compiled into the executable. This results in a single exe and no need for runtime dll's. Component publishers often offer delphi native versions of their ocx components.  The delphi executable is relatively large but no way near as big as the VB exe/dll combination.
 
A significant advantage is that the versioning problems that affect ocx's don't exist in delphi and you don't force the end user to download any large runtime dll's. (ocx's, incidentally, tend to be much larger than their delphi cousins).
 
However, delphi also offers the option of the VB approach (small exe and runtime dll's) and calls the dll's "packages".  The delphi method of implementing the dll approach is slightly more sophistocated than VB. Both approaches have their pros and cons.
 
Neither language can do much about ocx's, though delphi does at least offer an escape route."

How to create smaller EXEs?

Can't set string in routine?

Why does this display an empty dialog?

procedure Weird(Stuff : String);
begin
  Stuff := 'here';
end;
 
procedure TForm1.Button1Click(Sender: TObject);
var
  MyStuff : String;
 
begin
    Weird(MyStuff);
    ShowMessage(MyStuff);

Why can't I use String in MessageBox?

var
    MyTitle : String;
begin
      MessageBox('text', MyTitle, [smbOK]);

Is it possible to open more than one project at the same time?

Do I really need to call Free() after each Create(), or does Delphi frees memory when the program ends?

Yes, because unlike internal data types like String or Integer, objects must be created manually through Create() and freed with... Free().

As for the consequences of forgetting to call Free:

CodeGuard cannot report anything that takes place in Windows *after* your application terminates. It correctly reports that, at the time of termination, your application has failed to explicitly release some memory. Windows, barring some other error, tracks all memory allocations for a process and, upon termination, will free up that memory anyway. So that, in itself, is not the issue.
 
The issues are:
1) as long as your application *continues to run* it will be holding memory unnecessarily that cannot be used by other processes. If it is a repeated leak then eventually the system *will* run out of memory.
 
2) It isn't just a matter of memory but also other O/S resources. For example if the object you forget to free is holding open file handles or a COM or TCP port, or graphic resources, etc, then again that is impairing the operation of the system and, in some of these cases, it may be that they *won't* be fully cleaned up by Windows after the application terminates.
 
3) Simply bad programming practice to not cleanup properly.

Besides always adding a Try/Finally to .Free() any object, it's a good habit to check a projet with the FullDebugMode option of FastMM, especially during the initial construction phase of the project.

"[Fatal Error] File not found bla.dcu" after installing a new package

After installing a new design-time package (*.DPK) through File > Open > Install, you also need to add the path to its *.DCU files through Tools > Environment Options > Library, in the Library Path.

How to avoid interface freezing during long loops?

Application.ProcessMessage

Get an objet's methods/properties/events?

Some utilities (such as this one) use RTTI to read this from an object which requires upgrading to Delphi 2010 for full information (more basic information available through RTTI on previous versions of Delphi).

Get column datatype from dataset?

Here's how to get the datatype expected from a column in a dataset (untested):

uses
  TypInfo;
var
  aDataType: TDataType;
aDataType := MyQuery.FieldByName('FieldName').DataType;
ShowMessage(GetEnumName(TypeInfo(aDataType), Ord(aDataType));

Alternative:

//DataType is not a string, and therefore can't be typecast to a string -> Ord()
ShowMessage(IntToStr(Ord(ASQLite3Query1.Fields[myCol].DataType)));

Delphi Peeves

IDE

Language

How to display PNG on BitButn?

D2009 supports this, but not older versions. Take a look at these:

Places to find icons:

Resources

Learning Pascal

Learning Delphi

Sites

Books

Learning Delphi.Net

Tools

News