Question

I have form with MainMenu and I want to intercept when the user selects a command item from a menu. This works in Delphi:

type
  TForm1 = class(TForm)
    ... // Memo and MainMenu created
  protected
    procedure WMCommand(var Info: TWMCommand); message WM_COMMAND;
  end;


procedure TForm1.WMCommand(var Info: TWMCommand);
begin
  if (Info.ItemID < 10) then
    Memo1.Lines.Add( WMCommand   + IntToStr(Info.ItemID));
end;

In MainMenu I added some items and when I select those items from menu then my Memo1 is filled with:

WMCommand 2
WMCommand 3
WMCommand 3
WMCommand 2
WMCommand 5
...

I ported this application to FPC/Lazarus, but it seems that WM_COMMAND handler is not called! When I set breakpoint in TForm1.WMCommand in Delphi then Delphi stopped many times before main form appeared. Lazarus never stopped on this breakpoint. I think something is broken with WM_COMMAND in Lazarus, but maybe I don t know something. Any idea?

I use Lazarus 0.9.28.2 beta with FPC 2.2.4 on WinXP.

EDIT:

Using Winspector I checked that MainMenu generates WM_COMMAND:

WM_COMMAND
    Code: 0
    Control ID: 2
    Control HWND: 0x00000000
    Message Posted
    Time: 09:37:14.0968

I think there is bug in Lazarus/FPC in WM_COMMAND message method handling and I reported it: http://bugs.freepascal.org/view.php?id=15521

Answer 1

In a LCL application you have the following layers:

Application
LCL
Widget set Interface (e.g. win32/win64, qt, gtk2, carbon)
Widget set

WM_COMMAND is a winapi message from the widgetset Layer to the Widget Set interface layer. These messages are not passed to the higher layers, having portability in mind, other widget sets don t produce such messages.

If you want to capture the message, then you must write non-portable widgetset specific code (winapi code in this case). You can override the windowproc with setwindowlong. See the Lazarus wiki for an example.

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