Author: Tomas Rutkauskas 

How to intercept the maximize command

Answer:

If you want to restrict your window's maximum size (or minimum size, for that 
matter), you may try to intercept WM_SYSCOMMAND and check for the value of wParam.

More elegant is to intercept WM_GETMINMAXINFO, as the following example shows: 


1   type
2     TMyForm = class(TForm)
3       procedure _WM_GETMINMAXINFO(var mmInfo: TWMGETMINMAXINFO); message
4         wm_GetMinMaxInfo;
5     end;
6   
7     //..
8   
9   procedure TMyForm._WM_GETMINMAXINFO(var mmInfo: TWMGETMINMAXINFO);
10  begin
11    with mmInfo.minmaxinfo^ do
12    begin
13      // allow at most half of the screen, and position it in the middle
14      ptmaxposition.x := Screen.Width div 4;
15      ptmaxposition.y := Screen.Height div 4;
16  
17      ptmaxsize.x := Screen.Width div 2;
18      ptmaxsize.y := Screen.Height div 2;
19    end;
20  end;
21  
22  end.