简单使用EventBus

compile 'org.greenrobot:eventbus:3.1.1'

MessageEvent

package app.my.com.eventbus;

/**
 * Created by lenovo on 2017/11/29.
 */

public class MessageEvent {
    public boolean tag;

    public MessageEvent(boolean tag){
        this.tag = tag;
    }

    public boolean isTag() {
        return tag;
    }

    public void setTag(boolean tag) {
        this.tag = tag;
    }
}

MainActivity

package app.my.com.eventbus;

import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;

import org.greenrobot.eventbus.EventBus;
import org.greenrobot.eventbus.Subscribe;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Button bt1 = findViewById(R.id.bt1);
        bt1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                startActivity(new Intent(MainActivity.this, Main2Activity.class));
            }
        });

        EventBus.getDefault().register(this);

    }

    @Subscribe
    public void onMessageEvent(MessageEvent event) {
        System.out.println("event MainActivity = " + event.isTag());

        Toast.makeText(this, "message--------1", Toast.LENGTH_SHORT).show();

    }

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

Main2Activity

package app.my.com.eventbus;

import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;

import org.greenrobot.eventbus.EventBus;
import org.greenrobot.eventbus.Subscribe;

public class Main2Activity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main2);
        Button bt2 = findViewById(R.id.bt2);
        bt2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                startActivity(new Intent(Main2Activity.this,Main3Activity.class));
            }
        });
        EventBus.getDefault().register(this);
    }

    @Subscribe
    public void onMessageEvent(MessageEvent event){
        System.out.println("event Main2Activity = " + event.isTag());

        Toast.makeText(this, "message--------2", Toast.LENGTH_SHORT).show();

    }
}

Main3Activity

package app.my.com.eventbus;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;

import org.greenrobot.eventbus.EventBus;

public class Main3Activity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main3);
        Button bt3 = findViewById(R.id.bt3);
        bt3.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                EventBus.getDefault().post(new MessageEvent(true));
            }
        });
    }
}