//佈局兩個

//activity_ main

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
 
android:gravity="center"
android:orientation="vertical"
tools:context="com.example.eventbus.MainActivity">

    <Button
android:id="@+id/btn_try"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="btn_bty" />

    <TextView
android:id="@+id/tv"
android:layout_width=
 
"wrap_content"
android:layout_height="wrap_content"
android:text="tv" />

</LinearLayout>

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
 
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center"
tools:context="com.example.eventbus.SecondActivity">

    <Button
android:id="@+id/btn_first_event"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="點選傳值" />

</LinearLayout>

//MainActivity

package com.example.eventbus;

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

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

public class MainActivity extends AppCompatActivity {
    Button btn;
    TextView tv;
    @Override
protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        EventBus.getDefault().register(MainActivity.this);

        btn = (Button) findViewById(R.id.btn_try);
        tv = (TextView) findViewById(R.id.tv);

        btn.setOnClickListener(new View.OnClickListener() {
            @Override
public void onClick(View v) {
                // TODO Auto-generated method stub
//傳送訊息是使用EventBus中的Post方法來實現傳送的，傳送過去的是我們新建的類的例項！
Intent intent = new Intent(MainActivity.this,SecondActivity.class);
                startActivity(intent);
            }
        });
    }

    //必須要加這句話
//我們使用EventBus中最常用的onEventMainThread（）函式來接收訊息
@Subscribe(threadMode = ThreadMode.MAIN)
    public void onEventMainThread(FirstEvent event) {
        String msg = "onEventMainThread收到了訊息：" + event.getMsg();
        Log.d("harvic", msg);
        tv.setText(msg);
//            Toast.makeText(this, msg, Toast.LENGTH_LONG).show();
}


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

  }

public class FirstEvent {
    private String mMsg;

    public FirstEvent(String msg) {
        // TODO Auto-generated constructor stub
mMsg = msg;
    }

    public String getMsg() {
        return mMsg;
    }
}

public class SecondActivity extends AppCompatActivity {
    private Button btn_FirstEvent;
    @Override
protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_second);
        btn_FirstEvent = (Button) findViewById(R.id.btn_first_event);

        btn_FirstEvent.setOnClickListener(new View.OnClickListener() {

            @Override
public void onClick(View v) {
                // TODO Auto-generated method stub
EventBus.getDefault().post(new FirstEvent("我是Eventbus,你好!"));
                finish();
            }
        });
    }
}

compile 'org.greenrobot:eventbus:3.0.0'