How to check if a MDI child has been created or destroyed

Problem/Question/Abstract:

I have to write a kind of task list of all MDI child windows which are opened in the application. For this reason I tried to use the WM_PARENTNOTIFY to get an event, if a MDI child is created or destroyed. But I don't receive a message when the child windows are created or destroyed.

Answer:

Try the following:


const
  WM_AddWin = WM_User + 300;
  WM_DelWin = WM_User + 301;

type
  TForm1
    { ... }
  private

  procedure OnAddWindow(var msg: TMessage); message WM_AddWin;
  procedure OnDelWindow(var msg: TMessage); message WM_DelWin;
    public
end;

procedure TForm1.OnAddWindow(var msg: TMessage);
begin
  List.Add(Strpas(Pointer(msg.lparam)));
end;

procedure TForm1.OnDelWindow(var msg: TMessage);
begin
  List.delete(List.indexof(Strpas(Pointer(msg.lparam))));
end;

procedure OnChildFormCreate(Sender: TObject);
begin
  PostMessage(TForm(Owner).handle, WM_AddWin, 0, Integer(PChar('ChildFormname')));
end;

procedure OnChildFormDestroy;
begin
  PostMessage(TForm(Owner).handle, WM_DelWin, 0, Integer(PChar('ChildFormname')));
end;


This will post a message to the owner of a child form to add it to the master list and delete it
when it dies.