Author: Misha Moellner 

How to detect if Ctrl, Alt or Shift key is pressed

Answer:

1   function CtrlDown: Boolean;
2   var
3     State: TKeyboardState;
4   begin
5     GetKeyboardState(State);
6     Result := ((State[vk_Control] and 128) <> 0);
7   end;
8   
9   function ShiftDown: Boolean;
10  var
11    State: TKeyboardState;
12  begin
13    GetKeyboardState(State);
14    Result := ((State[vk_Shift] and 128) <> 0);
15  end;
16  
17  function AltDown: Boolean;
18  var
19    State: TKeyboardState;
20  begin
21    GetKeyboardState(State);
22    Result := ((State[vk_Menu] and 128) <> 0);
23  end;
24  
25  The following example demonstrates checking if the Shift key is pressed during a 
26  Button Click. 
27  
28  procedure TForm1.Button1Click(Sender: TObject);
29  begin
30    if ShiftDown then
31      Form1.Caption := 'Shift'
32    else
33      Form1.Caption := 'No Shift';
34  end;