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Frequently Asked Questions

Subclass the window procedure for a TForm

Question:

How can I subclass the window procedure for a TForm?

Answer:

Override the WinProc procedure for the form. The following example

overrides the window procedure for the form, and responds to the

WM_CANCELMODE message, indicating that a messagebox or other dialog

box has been executed.



Example:



type

  TForm1 = class(TForm)

    Button1: TButton;

    procedure WndProc (var Message: TMessage); override;

    procedure Button1Click(Sender: TObject);

  private

    { Private declarations }

  public

    { Public declarations }

  end;



var

  Form1: TForm1;



implementation



{$R *.DFM}



procedure TForm1.WndProc (var Message: TMessage);

begin

  if Message.Msg = WM_CANCELMODE then begin

    Form1.Caption := 'A dialog or message box has popped up';

  end else

  inherited

end;



procedure TForm1.Button1Click(Sender: TObject);

begin

  ShowMessage('Test Message');

end;

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