轉載請標明出處：http://blog.csdn.net/zhaoyanjun6/article/details/53065112
本文出自【趙彥軍的博客】

前言

• EventBus框架

  EventBus是一個通用的叫法，例如Google出品的Guava，Guava是一個龐大的庫，EventBus只是它附帶的一個小功能，因此實際項目中使用并不多。用的最多的是greenrobot/EventBus，這個庫的優點是接口簡潔，集成方便，但是限定了方法名，不支持注解。另一個庫square/otto修改自 Guava ，用的人也不少。所以今天我們研究的目標是greenrobot的EventBus.

• EventBus 簡介

  1、EventBus3.0.0 是最新的版本。
  2、EventBus 是Android 發布/訂閱事件總線，可簡化 Activities, Fragments, Threads, Services 等組件間的消息傳遞。
  3、可替代 Intent, Handler, BroadCast ，接口等傳統方案，更快，代碼更小，50K 左右的 jar 包，代碼更優雅，徹底解耦。

  github地址：https://github.com/greenrobot/EventBus

EventBus原理圖

如何添加依賴

• 在module的build.gredle 文件中的dependencies標簽中添加

  compile ‘org.greenrobot:eventbus:3.0.0’

  例如

apply plugin: 'com.android.application'android {compileSdkVersion 24buildToolsVersion "24.0.3"defaultConfig {applicationId "com.eventbus.app"minSdkVersion 14targetSdkVersion 24versionCode 1versionName "1.0"}buildTypes {release {minifyEnabled falseproguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'}} }dependencies {compile fileTree(dir: 'libs', include: ['*.jar'])compile 'com.android.support:appcompat-v7:24.2.1'compile 'org.greenrobot:eventbus:3.0.0' }

如何使用

• 注冊事件

  EventBus.getDefault().register( this );

• 取消注冊

  EventBus.getDefault().unregister( this );

• 發送數據

  EventBus.getDefault().post( “我發射了”);

簡單小例子：使用EventBus傳遞簡單字符串

package com.eventbus.app;import android.os.Bundle; import android.support.v7.app.AppCompatActivity; import android.view.View; import android.widget.Toast;import org.greenrobot.eventbus.EventBus; import org.greenrobot.eventbus.Subscribe; import org.greenrobot.eventbus.ThreadMode;public class MainActivity extends AppCompatActivity {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);//注冊EventBus.getDefault().register( this );findViewById( R.id.button).setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {EventBus.getDefault().post( "我發射了");}});}/*** 自定義一個方法 hello() ，用來接收事件。* 方法名字可以隨便寫* @return*/@Subscribe(threadMode = ThreadMode.MAIN)public void hello ( String event){/* Do something */Toast.makeText( this , event , Toast.LENGTH_SHORT).show();};@Overrideprotected void onDestroy() {super.onDestroy();//取消注冊 , 防止Activity內存泄漏EventBus.getDefault().unregister( this );} }

效果圖

線程模型

在接收事件消息的方法中，可以通過注解的方式設置線程模型，EventBus內置了4中線程模型，分別是ThreadMode.POSTING 、ThreadMode.MAIN、ThreadMode.BACKGROUND、ThreadMode.ASYNC

比如：

@Subscribe(threadMode = ThreadMode.POSTING)public void onMessageEventPostThread(String event) {Log.e( "event PostThread", "消息： " + event + " thread: " + Thread.currentThread().getName() );}@Subscribe(threadMode = ThreadMode.MAIN)public void onMessageEventMainThread(String event) {Log.e( "event MainThread", "消息： " + event + " thread: " + Thread.currentThread().getName());}@Subscribe(threadMode = ThreadMode.BACKGROUND)public void onMessageEventBackgroundThread(String event) {Log.e( "event BackgroundThread", "消息： " + event + " thread: " + Thread.currentThread().getName());}@Subscribe(threadMode = ThreadMode.ASYNC)public void onMessageEventAsync(String event) {Log.e( "event Async", "消息： " + event + " thread: " + Thread.currentThread().getName());}

• PostThread：如果使用事件處理函數指定了線程模型為PostThread，那么該事件在哪個線程發布出來的，事件處理函數就會在這個線程中運行，也就是說發布事件和接收事件在同一個線程。在線程模型為PostThread的事件處理函數中盡量避免執行耗時操作，因為它會阻塞事件的傳遞，甚至有可能會引起ANR。

• MainThread：如果使用事件處理函數指定了線程模型為MainThread，那么不論事件是在哪個線程中發布出來的，該事件處理函數都會在UI線程中執行。該方法可以用來更新UI，但是不能處理耗時操作。

• BackgroundThread：如果使用事件處理函數指定了線程模型為BackgroundThread，那么如果事件是在UI線程中發布出來的，那么該事件處理函數就會在新的線程中運行，如果事件本來就是子線程中發布出來的，那么該事件處理函數直接在發布事件的線程中執行。在此事件處理函數中禁止進行UI更新操作。

• Async：如果使用事件處理函數指定了線程模型為Async，那么無論事件在哪個線程發布，該事件處理函數都會在新建的子線程中執行。同樣，此事件處理函數中禁止進行UI更新操作。

小例子1： 在子線程發送數據

package com.eventbus.app;import android.os.Bundle; import android.support.v7.app.AppCompatActivity; import android.util.Log; import android.view.View;import org.greenrobot.eventbus.EventBus; import org.greenrobot.eventbus.Subscribe; import org.greenrobot.eventbus.ThreadMode;public class MainActivity extends AppCompatActivity {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);//注冊EventBus.getDefault().register( this );findViewById( R.id.button).setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {new Thread(new Runnable() {@Overridepublic void run() {Log.d( "event 發射數據線程 : " , Thread.currentThread().getName() ) ;EventBus.getDefault().post( "我發射了");}}).start() ;}});}@Subscribe(threadMode = ThreadMode.POSTING)public void onMessageEventPostThread(String event) {Log.e( "event PostThread", "消息： " + event + " thread: " + Thread.currentThread().getName() );}@Subscribe(threadMode = ThreadMode.MAIN)public void onMessageEventMainThread(String event) {Log.e( "event MainThread", "消息： " + event + " thread: " + Thread.currentThread().getName());}@Subscribe(threadMode = ThreadMode.BACKGROUND)public void onMessageEventBackgroundThread(String event) {Log.e( "event BackgroundThread", "消息： " + event + " thread: " + Thread.currentThread().getName());}@Subscribe(threadMode = ThreadMode.ASYNC)public void onMessageEventAsync(String event) {Log.e( "event Async", "消息： " + event + " thread: " + Thread.currentThread().getName());}@Overrideprotected void onDestroy() {super.onDestroy();//取消注冊 , 防止Activity內存泄漏EventBus.getDefault().unregister( this );} }

運行結果：

D/event 發射數據線程 :: Thread-109
E/event BackgroundThread: 消息： 我發射了 thread: Thread-109
E/event PostThread: 消息： 我發射了 thread: Thread-109
E/event Async: 消息： 我發射了 thread: pool-1-thread-2
E/event MainThread: 消息： 我發射了 thread: main

小例子2： 在主線程發送數據

package com.eventbus.app;import android.os.Bundle; import android.support.v7.app.AppCompatActivity; import android.util.Log; import android.view.View;import org.greenrobot.eventbus.EventBus; import org.greenrobot.eventbus.Subscribe; import org.greenrobot.eventbus.ThreadMode;public class MainActivity extends AppCompatActivity {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);//注冊EventBus.getDefault().register( this );findViewById( R.id.button).setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {Log.d( "event 發射數據線程 : " , Thread.currentThread().getName() ) ;EventBus.getDefault().post( "我發射了");}});}@Subscribe(threadMode = ThreadMode.POSTING)public void onMessageEventPostThread(String event) {Log.e( "event PostThread", "消息： " + event + " thread: " + Thread.currentThread().getName() );}@Subscribe(threadMode = ThreadMode.MAIN)public void onMessageEventMainThread(String event) {Log.e( "event MainThread", "消息： " + event + " thread: " + Thread.currentThread().getName());}@Subscribe(threadMode = ThreadMode.BACKGROUND)public void onMessageEventBackgroundThread(String event) {Log.e( "event BackgroundThread", "消息： " + event + " thread: " + Thread.currentThread().getName());}@Subscribe(threadMode = ThreadMode.ASYNC)public void onMessageEventAsync(String event) {Log.e( "event Async", "消息： " + event + " thread: " + Thread.currentThread().getName());}@Overrideprotected void onDestroy() {super.onDestroy();//取消注冊 , 防止Activity內存泄漏EventBus.getDefault().unregister( this );} }

運行結果：

D/event 發射數據線程 :: main
E/event MainThread: 消息： 我發射了 thread: main
E/event PostThread: 消息： 我發射了 thread: main
E/event Async: 消息： 我發射了 thread: pool-1-thread-3
E/event BackgroundThread: 消息： 我發射了 thread: pool-1-thread-4

黏性事件

除了上面講的普通事件外，EventBus還支持發送黏性事件。何為黏性事件呢？簡單講，就是在發送事件之后再訂閱該事件也能收到該事件，跟黏性廣播類似。具體用法如下：

• 注冊

  EventBus.getDefault().register( this );

• 事件接收

  @Subscribe(threadMode = ThreadMode.MAIN , sticky = true )
  public void onMessageEventMainThread(String event) {
  Log.e( “event MainThread”, “消息： ” + event + ” thread: ” + > Thread.currentThread().getName());
  }

• 取消注冊

  EventBus.getDefault().unregister( this ) ;

• 發送事件

  EventBus.getDefault().postSticky( “我發射了”);

小例子：在MainActivity發送事件，在Activity2里注冊并且接收事件

MainActivity源碼

package com.eventbus.app;import android.content.Intent; import android.os.Bundle; import android.support.v7.app.AppCompatActivity; import android.util.Log; import android.view.View;import org.greenrobot.eventbus.EventBus;public class MainActivity extends AppCompatActivity {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);findViewById( R.id.button).setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {Log.d( "event 發射數據線程 : " , Thread.currentThread().getName() ) ;EventBus.getDefault().postSticky( "我發射了");startActivity( new Intent( MainActivity.this , Activity2.class ));}});} }

Activity2源碼

package com.eventbus.app;import android.support.v7.app.AppCompatActivity; import android.os.Bundle; import android.util.Log;import org.greenrobot.eventbus.EventBus; import org.greenrobot.eventbus.Subscribe; import org.greenrobot.eventbus.ThreadMode;public class Activity2 extends AppCompatActivity {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_2);//注冊EventBus.getDefault().register( this );}@Subscribe(threadMode = ThreadMode.MAIN , sticky = true )public void onMessageEventMainThread(String event) {Log.e( "event MainThread", "消息： " + event + " thread: " + Thread.currentThread().getName());}@Overrideprotected void onDestroy() {super.onDestroy();//取消注冊 , 防止Activity內存泄漏EventBus.getDefault().unregister( this ) ;} }

這就是粘性事件，能夠收到訂閱之前發送的消息。但是它只能收到最新的一次消息，比如說在未訂閱之前已經發送了多條黏性消息了，然后再訂閱只能收到最近的一條消息。

EventBus源碼分析

• Subscribe 接口源碼

@Documented @Retention(RetentionPolicy.RUNTIME) @Target({ElementType.METHOD}) public @interface Subscribe {ThreadMode threadMode() default ThreadMode.POSTING;/*** If true, delivers the most recent sticky event (posted with* {@link EventBus#postSticky(Object)}) to this subscriber (if event available).*/boolean sticky() default false;/** Subscriber priority to influence the order of event delivery.* Within the same delivery thread ({@link ThreadMode}), higher priority subscribers will receive events before* others with a lower priority. The default priority is 0. Note: the priority does *NOT* affect the order of* delivery among subscribers with different {@link ThreadMode}s! */int priority() default 0; }

可以看出默認的線程模型是ThreadMode.POSTING ；默認黏性事件為false,也就是默認不開啟黏性事件；默認的優選級為0 。

• EventBus 類部分源碼

static volatile EventBus defaultInstance;/** Convenience singleton for apps using a process-wide EventBus instance. */public static EventBus getDefault() {if (defaultInstance == null) {synchronized (EventBus.class) {if (defaultInstance == null) {defaultInstance = new EventBus();}}}return defaultInstance;}

getDefault() 是一個單例模式 , 只有一個實例對象。

• ThreadMode 類源碼

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 }

這個類是枚舉類，定義了線程模型中的幾種類型。

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參考資料

【EventBus 3.0的用法詳解】
【EventBus使用詳解】
【騰訊Bugly干貨】老司機教你“飆”EventBus3】

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