关于EventBus3.0使用，你看这篇就够了

作为一枚Android开发者，关于EventBus相信应该都听说过。要是用过就请忽略本文，本文讲得比较基础。
要是没用过，建议你花两分钟看看。

目前EventBus最新版本是3.0，本demo基于3.0编写的。

GitHub : https://github.com/greenrobot/EventBus
官方文档：http://greenrobot.org/eventbus/documentation

一、EventBus概述

EventBus是一个Android端优化的publish/subscribe消息总线，简化了应用程序内各组件间、组件与后台线程间的通信。

作为一个消息总线主要有三个组成部分：

• 事件（Event）
• 事件订阅者（Subscriber）

• 事件发布者（Publisher）

  

  官方提供的关系图

二、EventBus用法

1、把EventBus依赖到项目

build.gradle添加引用

compile 'org.greenrobot:eventbus:3.0.0'

Maven

<dependency>
    <groupId>org.greenrobot</groupId>
    <artifactId>eventbus</artifactId>
    <version>3.0.0</version>
</dependency>

或者直接下载EventBus 架包jar 放到项目中

2、构造发送消息类，也就是发送的对象

public class MainMessage{

    private String message;

    public String getMessage() {
        return message;
    }

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

3、注册/解除注册

EventBus.getDefault().register(this);//注册

EventBus.getDefault().unregister(this);//解除注册

4 、发送消息

EventBus.getDefault().post(new MainMessage("你好，爱开发");

ThreadMode总共四个：

• MAIN UI主线程

• POSTING 默认调用方式，在调用post方法的线程执行，避免了线程切换，性能开销最少

• BACKGROUND 如果调用post方法的线程不是主线程，则直接在该线程执行。
  如果是主线程，则切换到后台单例线程，多个方法公用同个后台线程，按顺序执行，避免耗时操作

• ASYNC 开辟新独立线程，用来执行耗时操作，例如网络访问。

来看一下源码，ThreadMode也就一个枚举，英文自己对照理解吧，不是很复杂

public enum ThreadMode {
    /**
     * Subscriber will be called in the same thread, which is posting the event. This is the default. Event delivery
     * implies the least overhead because it avoids thread switching completely. Thus this is the recommended mode for
     * simple tasks that are known to complete is a very short time without requiring the main thread. Event handlers
     * using this mode must return quickly to avoid blocking the posting thread, which may be the main thread.
     */
    POSTING,

    /**
     * Subscriber will be called in Android's main thread (sometimes referred to as UI thread). If the posting thread is
     * the main thread, event handler methods will be called directly. Event handlers using this mode must return
     * quickly to avoid blocking the main thread.
     */
    MAIN,

    /**
     * Subscriber will be called in a background thread. If posting thread is not the main thread, event handler methods
     * will be called directly in the posting thread. If the posting thread is the main thread, EventBus uses a single
     * background thread, that will deliver all its events sequentially. Event handlers using this mode should try to
     * return quickly to avoid blocking the background thread.
     */
    BACKGROUND,

    /**
     * Event handler methods are called in a separate thread. This is always independent from the posting thread and the
     * main thread. Posting events never wait for event handler methods using this mode. Event handler methods should
     * use this mode if their execution might take some time, e.g. for network access. Avoid triggering a large number
     * of long running asynchronous handler methods at the same time to limit the number of concurrent threads. EventBus
     * uses a thread pool to efficiently reuse threads from completed asynchronous event handler notifications.
     */
    ASYNC
}

5 、事件处理

//ui主线程中执行
@Subscribe(threadMode = ThreadMode.Main) 

public void onMainEventBus(MainMessage msg) {
}

6、priority事件优先级

//priority越大，级别越高
@Subscribe(threadMode = ThreadMode.MAIN,priority = 100)
public void onEvent(MainMessage event) {
}

7、终止事件传递

// 注意中止事件传递，后续事件不在调用

@Subscribe
public void onEvent(MessageEvent event){
    EventBus.getDefault().cancelEventDelivery(event) ;
}

下面我们来看一个完整的demo
先看一下效果图：

3.gif

新建两个activity，分别为MainActivity和 SecondActivity

其中MainActivity来放了五个按钮和一个文本框
SecondActivity只有一个按钮，点击按钮通知MainActivity页面更新。

看一下MainActivity主要代码：

     /**
     * 主线程中执行
     *
     * @param msg
     */
    @Subscribe(threadMode = ThreadMode.MAIN)
    public void onMainEventBus(MainMessage msg) {
        Log.e(TAG, msg.getMessage());
        tv_desc.setText(msg.getMessage());
    }

    /**
     * 后台线程
     *
     * @param msg
     */
    @Subscribe(threadMode = ThreadMode.BACKGROUND)
    public void onBackgroundEventBus(BackgroundMessage msg) {
        Log.e(TAG, msg.getMessage());
    }

    /**
     * 异步线程
     *
     * @param msg
     */
    @Subscribe(threadMode = ThreadMode.ASYNC)
    public void onAsyncEventBus(AsyncMessage msg) {
        Log.e(TAG, msg.getMessage());

    }

    /**
     * 默认情况，和发送事件在同一个线程
     *
     * @param msg
     */
    @Subscribe(threadMode = ThreadMode.POSTING)
    public void onPostEventBus(PostingMessage msg) {

        Log.e(TAG, msg.getMessage());
    }

按钮点击事件

@Override
    public void onClick(View v) {
        switch (v.getId()) {
            case R.id.btnMain:
                EventBus.getDefault().post(new MainMessage("MainMessage"));
                break;
            case R.id.btnBackground:
                EventBus.getDefault().post(new BackgroundMessage("BackgroundMessage"));
                break;
            case R.id.btnAsync:
                EventBus.getDefault().post(new AsyncMessage("AsyncMessage"));
                break;
            case R.id.btnPosting:
                EventBus.getDefault().post(new PostingMessage("PostingMessage"));
                break;
            case R.id.btn1:
                Intent intent = new Intent(MainActivity.this, SecondActivity.class);
                startActivity(intent);
                break;

        }
    }

分别点击前面四个按钮时控制台按顺序输出：

点击前面四个按钮时控制台输出

SecondActivity页面点击发送消息的事件

EventBus.getDefault().post(new MainMessage("传递信息：aikaifa"));

在MianActivity页面我们就能接受到SecondActivity传递过来的信息了。
如果感兴趣想跑一下项目，源码请戳这里

作者：洪生鹏
链接：https://www.jianshu.com/p/f9aabe9d4eca
來源：简书
简书著作权归作者所有，任何形式的转载都请联系作者获得授权并注明出处。