Как перехватить нажатие TAB?

Code:

unit Hndltabu;

interface

uses

SysUtils, WinTypes, WinProcs, Messages, Classes,

Graphics, Controls, Forms, Dialogs, StdCtrls;

type

TForm1 = class(TForm)

   Edit1: TEdit;

   Edit2: TEdit;

   Label1: TLabel;

   procedure FormCreate(Sender: TObject);

private { Private-Deklarationen }

   procedure AppMessage(var Msg: TMsg; var Handled: Boolean);

public { Public-Deklarationen }

end;

var

Form1: TForm1;

implementation

{$R *.DFM}

procedure TForm1.AppMessage(var Msg: TMsg; var Handled: Boolean);

const

shiftPressed: boolean = false;

begin

if Msg.Message = WM_KEYDOWN then

   if not shiftPressed and (Msg.wParam = VK_SHIFT) then

   begin

     shiftPressed := true;

     Exit;

   end

   else

   begin

     if Msg.wParam = VK_TAB then

       if ActiveControl = Edit1 then

       begin

         if shiftPressed then

           Label1.Caption := 'BACKTAB!'

         else

           Label1.Caption := 'TAB!';

         Handled := true

       end

       else

         Label1.Caption := '';

     shiftPressed := false;

   end;

end;

procedure TForm1.FormCreate(Sender: TObject);

begin

Application.OnMessage := AppMessage;

end;

end.