Agfdhyk

I have a main Form and when I select an item and press Enter a second modal Form is shown. This has some TEdit controls to change the item parameters. When the user has finished, he can press Esc to cancel or Enter to update the item, and close the edit Form.

The problem is that if the user presses and holds Enter, a loop is occurs. The Form is closed and opened again and then closed... and so on.

I changed the WndProc of the modal Form and cancel if the previous key state was pressed. But this works only if I don't have any controls on the Form. If I drop a TEdit (which is needed), the Form re-enters the loop. The modal Form has KeyPreview set to true, because I want to be able to validate the data from anywhere.

This is the minimal code to reproduce the problem:

After you test this, you can drop a TEdit on Form2 and you will notice that a loop occurs.

Form1:

unit Unit1;



interface



uses

  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,

  Dialogs, StdCtrls;



type

  TForm1 = class(TForm)

    procedure FormKeyPress(Sender: TObject; var Key: Char);

  end;



var

  Form1: TForm1;



implementation



uses Unit2;



{$R *.dfm}



procedure TForm1.FormKeyPress(Sender: TObject; var Key: Char);

begin

 if Key = #13 then Form2.ShowModal;

end;



end.

Form2:

unit Unit2;



interface



uses

  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,

  Dialogs, StdCtrls;



type

  TForm2 = class(TForm)

    Edit1: TEdit;

    procedure FormCreate(Sender: TObject);

    procedure FormKeyPress(Sender: TObject; var Key: Char);

  protected

    procedure WndProc(var Msg: TMessage); override;

  end;



var

  Form2: TForm2;



implementation



{$R *.dfm}



procedure TForm2.FormCreate(Sender: TObject);

begin

 KeyPreview:= True;

end;



procedure TForm2.FormKeyPress(Sender: TObject; var Key: Char);

begin

 if Key = #13 then begin Key:= #0; ModalResult:= mrOK; end;

end;



procedure TForm2.WndProc(var Msg: TMessage);

begin

 if (Msg.Msg = WM_CHAR) and ((Msg.LParam and $40000000) <> 0) then Exit;

 inherited;

end;



end.

Because it's impossible to hook TWinControl.DoKeyPress to solve this issue as it should, I came up with this workaround:

Form1:

procedure TForm1.FormCreate(Sender: TObject);

begin

 Application.OnActivate:= AppActivate;

end;



procedure TForm1.AppActivate(Sender: TObject);

begin

 EnterReleased:= (GetAsyncKeyState(VK_RETURN) and $8000) = 0;

end;



procedure TForm1.FormKeyPress(Sender: TObject; var Key: Char);

begin

 if Key = #13 then begin

  Key:= #0;

  if EnterReleased then begin

   EnterReleased:= False;

   Form2.ShowModal;

  end;

 end;

end;



procedure TForm1.FormKeyUp(Sender: TObject; var Key: Word; Shift: TShiftState);

begin

 if Key = VK_RETURN then EnterReleased:= True;

end;

Form2:

procedure TForm2.FormCreate(Sender: TObject);

begin

 KeyPreview:= True;

end;



procedure TForm2.FormKeyPress(Sender: TObject; var Key: Char);

begin

 if Key = #13 then begin

  Key:= #0;

  if EnterReleased then begin

   EnterReleased:= False;

   ModalResult:= mrOK;

  end;

 end;

end;



procedure TForm2.FormKeyUp(Sender: TObject; var Key: Word; Shift: TShiftState);

begin

 if Key = VK_RETURN then EnterReleased:= True;

end;