Acitivty的子类 基础该类的子类必须实现onCreate 方法 * 在该类中注册了一个BroadcastReceiver 用于接收退出消息 * 在接收到消息之后结束自身-Acitivty basis of a subclass of a subclass must implement the class method* onCreate registered in the class to receive a BroadcastReceiver quit message* th