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(yōu)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(fā)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(tǒng)方案，更快，代碼更小，50K 左右的 jar 包，代碼更優(yōu)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 24 buildToolsVersion "24.0.3" defaultConfig { applicationId "com.eventbus.app" minSdkVersion 14 targetSdkVersion 24 versionCode 1 versionName "1.0" } buildTypes { release { minifyEnabled false proguardFiles 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(fā)送數(shù)據(jù)
EventBus.getDefault().post( "我發(fā)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 { @Override protected 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() { @Override public void onClick(View v) { EventBus.getDefault().post( "我發(fā)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(); }; @Override protected void onDestroy() { super.onDestroy(); //取消注冊 , 防止Activity內(nèi)存泄漏 EventBus.getDefault().unregister( this ); }}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(shè)置線程模型，EventBus內(nèi)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(shù)指定了線程模型為PostThread，那么該事件在哪個線程發(fā)布出來的，事件處理函數(shù)就會在這個線程中運行，也就是說發(fā)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(shù)中盡量避免執(zhí)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(shù)指定了線程模型為MainThread，那么不論事件是在哪個線程中發(fā)布出來的，該事件處理函數(shù)都會在UI線程中執(zhí)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(shù)指定了線程模型為BackgroundThread，那么如果事件是在UI線程中發(fā)布出來的，那么該事件處理函數(shù)就會在新的線程中運行，如果事件本來就是子線程中發(fā)布出來的，那么該事件處理函數(shù)直接在發(fā)布事件的線程中執(zhí)行。在此事件處理函數(shù)中禁止進行UI更新操作。
Async：如果使用事件處理函數(shù)指定了線程模型為Async，那么無論事件在哪個線程發(fā)布，該事件處理函數(shù)都會在新建的子線程中執(zhí)行。同樣，此事件處理函數(shù)中禁止進行UI更新操作。
小例子1： 在子線程發(fā)送數(shù)據(jù)
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 { @Override protected 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() { @Override public void onClick(View v) { new Thread(new Runnable() { @Override public void run() { Log.d( "event 發(fā)射數(shù)據(jù)線程 : " , Thread.currentThread().getName() ) ; EventBus.getDefault().post( "我發(fā)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()); } @Override protected void onDestroy() { super.onDestroy(); //取消注冊 , 防止Activity內(nèi)存泄漏 EventBus.getDefault().unregister( this ); }}運行結(jié)果：
D/event 發(fā)射數(shù)據(jù)線程 :: Thread-109
E/event BackgroundThread: 消息： 我發(fā)射了 thread: Thread-109
E/event PostThread: 消息： 我發(fā)射了 thread: Thread-109
E/event Async: 消息： 我發(fā)射了 thread: pool-1-thread-2
E/event MainThread: 消息： 我發(fā)射了 thread: main
小例子2： 在主線程發(fā)送數(shù)據(jù)
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 { @Override protected 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() { @Override public void onClick(View v) { Log.d( "event 發(fā)射數(shù)據(jù)線程 : " , Thread.currentThread().getName() ) ; EventBus.getDefault().post( "我發(fā)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()); } @Override protected void onDestroy() { super.onDestroy(); //取消注冊 , 防止Activity內(nèi)存泄漏 EventBus.getDefault().unregister( this ); }}運行結(jié)果：
D/event 發(fā)射數(shù)據(jù)線程 :: main
E/event MainThread: 消息： 我發(fā)射了 thread: main
E/event PostThread: 消息： 我發(fā)射了 thread: main
E/event Async: 消息： 我發(fā)射了 thread: pool-1-thread-3
E/event BackgroundThread: 消息： 我發(fā)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(fā)送黏性事件。何為黏性事件呢？簡單講，就是在發(fā)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(fā)送事件
EventBus.getDefault().postSticky( "我發(fā)射了");
小例子：在MainActivity發(fā)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 { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); findViewById( R.id.button).setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { Log.d( "event 發(fā)射數(shù)據(jù)線程 : " , Thread.currentThread().getName() ) ; EventBus.getDefault().postSticky( "我發(fā)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 { @Override protected 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()); } @Override protected void onDestroy() { super.onDestroy(); //取消注冊 , 防止Activity內(nèi)存泄漏 EventBus.getDefault().unregister( this ) ; }}這就是粘性事件，能夠收到訂閱之前發(fā)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(jīng)發(fā)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(yōu)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。
以上這篇Android EventBus 3.0.0 使用總結(jié)(必看篇)就是小編分享給大家的全部內(nèi)容了，希望能給大家一個參考，也希望大家多多支持VEVB武林網(wǎng)。
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