Author: Tomas Rutkauskas

I have 4 buttons on a form, let's say button1 and button2 on the left side on the 
form and button3 and button4 on the right side on the form. When Button1 has the 
focus and I press the RightArrow I want to have Button3 to get the focus instead of 
Button2. When Button3 has the focus and I press the LeftArrow I want to have 
Button1 to get the focus. I've tried the onkeydown event on the button but it 
ignores to trap the arrowkeys.

Answer:

Buttons do not process navigation keys, so they go to the form in the guise of 
CM_DIALOGKEY messages and the form processes them to move to the next/ previous 
control in tab order. You may be able to achieve what you want by simply changing 
the tab order of your buttons (assuming they are all sitting on the same parent 
control).

To handle this all yourself you would add a handler for the CM_DIALOGKEY message to 
the form.

1   {form private section}
2   
3   procedure CMDialogKey(var msg: TCMDialogKey); message CM_DIALOGKEY;
4   
5     procedure TForm1.CMDialogKey(var msg: TCMDialogKey);
6     begin
7       case Msg.Charcode of
8         VK_RIGHT:
9           begin
10            if ActiveControl = Button1 then
11            begin
12              Button3.Setfocus;
13              msg.result := 1; {mark key handled}
14              Exit;
15            end;
16            if ActiveControl = Button2 then
17            begin
18              Button4.Setfocus;
19              msg.result := 1; {mark key handled}
20              Exit;
21            end;
22          end;
23        VK_LEFT:
24          begin
25            if ActiveControl = Button3 then
26            begin
27              Button1.Setfocus;
28              msg.result := 1;
29              Exit;
30            end;
31            if ActiveControl = Button4 then
32            begin
33              Button2.Setfocus;
34              msg.result := 1;
35              Exit;
36            end;
37          end;
38      end;
39      inherited;
40    end;
41  end;