观察者模式EventBus

 implementation ‘org.greenrobot:eventbus:3.1.1‘

public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        EventBus.getDefault().register(this);
        MessageEvent messsge = new MessageEvent("消息");
        EventBus.getDefault().post(messsge);
    }
    @Subscribe(threadMode = ThreadMode.MAIN)//必须指定线程模式
    public void Subscribe(MessageEvent messageEvent) {
        String message = messageEvent.getMessage();
        System.out.println(message);
    }
    public class MessageEvent{
        private String message;
        public  MessageEvent(String message){
            this.message=message;
        }
        public String getMessage() {
            return message;
        }

        public void setMessage(String message) {
            this.message = message;
        }
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        EventBus.getDefault().unregister(this);

    }
}