Author: Tomas Rutkauskas
Traverse the global list of all windows

Answer:

Sometimes you may want to do something with all windows (and controls) on the 
screen, including non-Delphi windows.

For such a purpose, you will use the API function EnumWindows. The following code 
includes the calls MakeProcInstance/ FreeProcInstance, which are needed in 
16bit-Windows (including Delphi 1 under Win95).

This sample code hides every existing window.. a rather useless example, but after 
all, it's just an example.

1   
2   function NextWindow(Wnd: HWnd; Form: TForm1): Boolean; export;
3   {$IFDEF Win32} stdcall;
4   {$ENDIF}
5   begin
6     ShowWindow(Wnd, SW_HIDE);
7     NextWindow := true; { next window, please }
8   end;
9   
10  procedure TForm1.Sample;
11  var
12    EnumProc: TFarProc;
13  begin
14    { this works in Win32 }
15    EnumWindows(@NextWindow, LongInt(Self));
16  
17    { MakeProcInstance for Win16 }
18    EnumProc := MakeProcInstance(@NextWindow, HInstance);
19    EnumWindows(EnumProc, 0);
20    FreeProcInstance(EnumProc);
21  end;