Author: Jonas Bilinkevicius

How to disable the close button of a TForm

Answer:

Solve 1:
1   
2   procedure EnableCloseButton(const bEnable: Boolean);
3   const
4     MenuFlags: array[Boolean] of Integer = (MF_DISABLED, MF_ENABLED);
5   var
6     hSysMenu: HMENU;
7   begin
8     hSysMenu := GetSystemMenu(Handle, False);
9     if hSysMenu > 0 then
10      EnableMenuItem(hSysMenu, SC_CLOSE, MF_BYCOMMAND or MenuFlags[bEnable]);
11  end;



Solve 2:

The usual approach is to disable or enable the corresponding item in the forms 
system menu. However, that does not work for all of them. You can always trap the 
WM_SYSCOMMAND message caused by clicking on the items and not pass it on, but this 
way the border icons do not appear disabled.

12  { ... }
13  EnableMenuItem(GetSystemMenu(handle, False), SC_CLOSE, MF_BYCOMMAND or MF_GRAYED); 
        

That will disable the close box, for example.


Solve 3:

Remember that certain combinations will cause different results (ie. removing the 
system menu will also disable minimize/ maximize etc.)

14  procedure TForm1.Button1Click(Sender: TObject);
15  var
16    Style: Integer;
17  begin
18    Style := GetWindowLong(Handle, GWL_STYLE);
19    {disable minimize}
20    Style := Style - WS_MINIMIZEBOX;
21    {disable maximize}
22    Style := Style - WS_MAXIMIZEBOX;
23    {remove system menu}
24    Style := Style - WS_SYSMENU;
25    {set new style}
26    SetWindowLong(Handle, GWL_STYLE, Style);
27    {repaint the title bar}
28    RedrawWindow(Handle, nil, 0, RDW_FRAME or RDW_INVALIDATE);
29  end;