用sendmessage 发送消息，但onmessage还是能获取到，求助~

procedure TForm1.ApplicationEvents1Message(var Msg: tagMSG; var Handled: Boolean);
begin
  if Msg.message = WM_LBUTTONDOWN then
  begin
//    mmo1.Lines.Add('OnMessage');
    ShowMessage('OnMessage');
    Handled := True;
  end;
end;

procedure TForm1.btn1Click(Sender: TObject);
begin
  SendMessage(Self.Handle, WM_LBUTTONDOWN, 0, 0);
//  Perform(WM_LBUTTONDOWN, 0, 0);
//  PostMessage(Self.Handle, WM_LBUTTONDOWN, 0, 0);
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  mmo1.Clear;
end;

[解决办法]
楼主想达到什么效果？