当用户点击通知上的按钮时，将始终显示主界面控制器.在主控制器上调用handleActionWithIdentifier:forRemoteNotification:，您可以在那里更新UI.例如，您可以隐藏某些元素，或按其他控制器.

When the user taps a button on the notification, the main interface controller is always displayed. handleActionWithIdentifier:forRemoteNotification: is called on your main controller and you can update the UI there. For example, you could hide certain elements, or push a different controller.

(如果用户点击窗扇，则标识符将为空字符串.)

(If the user taps on the sash, the identifier will be an empty string.)