procedure TfrmMain.FormKeyDown(Sender: TObject; var Key: Word;
  var KeyChar: Char; Shift: TShiftState);
begin
  if Key = vkMenu then
  begin
    //如果没有显示则显示，否则隐藏
    if pnlMainMenu.Visible then
      pnlMainMenu.Visible := False
    else
    begin
      //清除选择项
      ListBox1.ClearSelection;
      //显示菜单
      pnlMainMenu.Visible := true;
    end;
  end;
end;

procedure TfrmMain.ListBoxItem1Click(Sender: TObject);
begin
  ShowMessage((Sender as TListBoxItem).Text);
  pnlMainMenu.Visible := False;
end;

procedure TfrmMain.FormMouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Single);
begin
  pnlMainMenu.Visible := False;
end;