Author: Jonas Bilinkevicius

Is it possible to limit the MDI client form movement, so that the form cannot be 
moved outside the client area of the MDI form?

Answer:

Yes, you can handle the WM_WINDOWPOSCHANGING message in the child forms and modify 
the message parameters if needs be to keep the child fully visible. Of course this 
is a breach of the standard Windows behaviour.

1   private {in form declaration}
2   
3   procedure WMWINDOWPOSCHANGING(var msg: TWMWINDOWPOSCHANGING);
4     message WM_WINDOWPOSCHANGING;
5   
6   procedure TForm1.WMWINDOWPOSCHANGING(var msg: TWMWINDOWPOSCHANGING);
7   var
8     r: TRect;
9   begin
10    with msg.Windowpos^ do
11    begin
12      if (flags and SWP_NOMOVE) = 0 then
13      begin
14        r := GetClientrect(Application.Mainform.handle, r);
15        if x < 0 then
16          x := 0;
17        if y < 0 then
18          y := 0;
19        if (x + cx) > r.right then
20          x := r.right - cx;
21        if (y + cy) > r.bottom then
22          y := r.bottom - cy;
23      end;
24      inherited;
25    end;
26  end;