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#155: To show the system menu

As you know, every form/window in MS Windows (TForm in VCL terms) have a system menu. Usually there are pre-defined items like Close, Mimimize, Maximize, Move etc

But, of course, you also may add any own item in this system menu (see my tip#30 for sample)

So sometimes you may want to show this system menu for form but in any own position and from any your event. For example, user'll click on some your button and will see this system menu:

procedure TForm1.Button1Click(Sender: TObject);
var
  hMenuHandle: hMENU;
  hMenuItem: dWord;
  p: TPoint;
begin
  {recalculate button coordinates to screen coordinates}
  p.X := Button1.Left;
  p.Y := Button1.Top;
  p := Button4.ClientToScreen(p);

  hMenuHandle := GetSystemMenu(Handle, False);
  hMenuItem := LongWord(Windows.TrackPopupMenu(hMenuHandle, TPM_LEFTBUTTON or
                                               TPM_RIGHTBUTTON or TPM_RETURNCMD,
                                               p.X, p.Y, 0, Handle, nil));
  if hMenuItem > 0 then
    SendMessage(Handle, WM_SYSCOMMAND, hMenuItem, 0);
end;

This could be really useful if you replace standard caption and draw own "header". Generally better for this task to process the WM_NCPAINT and WM_NCHITTEST messages but I saw a few implementations without these messages too...


Published: July 28, 2002

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