弹出菜单
Menus通常将直接被加入到窗口中，但也可以通过鼠标单击来临时显示他们。例如当用户单击鼠标右键的时候，可能需要显示上下文菜单。
例如：
Glib::ustring ui_info =
"<interface>"
" <menu id='menu-examplepopup'>"
" <section>"
" <item>"
" <attribute name='label' translatable='yes'>Edit</attribute>"
" <attribute name='action'>examplepopup.edit</attribute>"
" </item>"
" <item>"
" <attribute name='label' translatable='yes'>Process</attribute>"
" <attribute name='action'>examplepopup.process</attribute>"
" </item>"
" <item>"
" <attribute name='label' translatable='yes'>Remove</attribute>"
" <attribute name='action'>examplepopup.remove</attribute>"
" </item>"
" </section>"
" </menu>"
"</interface>";
m_refBuilder->add_from_string(ui_info);
auto gmenu = m_refBuilder->get_object<Gio::Menu>("menu-examplepopup");
m_pMenuPopup = std::make_unique<Gtk::Menu>(gmenu);
要显示弹出菜单，请使用Gtk::Menu的popup()方法，无论如何你都需要处理由button_press_event信号提供的激活时机（鼠标单双三击、按下还是释放）和按钮标识（哪个鼠标按键）。例如：
bool ExampleWindow::on_button_press_event(GdkEventButton* event)
{
if( (event->type == GDK_BUTTON_PRESS) && (event->button == 3) )
{
if(!m_pMenuPopup->get_attach_widget())
m_pMenuPopup->attach_to_widget(*this);
m_pMenuPopup->popup(event->button, event->time);
return true; //It has been handled.
}
else
return false;
}