Петр

trayMenu = new ContextMenu();
var items = trayMenu.MenuItems;
items.Add("Open", OnOpenMainWindow);
items.Add("-");
items.Add("Quit", OnQuitApplication);

private void OnOpenMainWindow(object sender, EventArgs e)
{
     Visible = true;
     ShowInTaskbar = true;
}

Toast toast = Toast.makeText(m_activity, message, Toast.LENGTH_SHORT);
toast.show();
toast.cancel();