Android EventBus 3.0.0 使用總結(jié)(必看篇)

更新時(shí)間：2017年05月17日 13:24:19 投稿：jingxian

下面小編就為大家?guī)硪黄狝ndroid EventBus 3.0.0 使用總結(jié)(必看篇)。小編覺得挺不錯(cuò)的，現(xiàn)在就分享給大家，也給大家做個(gè)參考。一起跟隨小編過來看看吧

前言

EventBus框架

EventBus是一個(gè)通用的叫法，例如Google出品的Guava，Guava是一個(gè)龐大的庫(kù)，EventBus只是它附帶的一個(gè)小功能，因此實(shí)際項(xiàng)目中使用并不多。用的最多的是greenrobot/EventBus，這個(gè)庫(kù)的優(yōu)點(diǎn)是接口簡(jiǎn)潔，集成方便，但是限定了方法名，不支持注解。另一個(gè)庫(kù)square/otto修改自 Guava ，用的人也不少。所以今天我們研究的目標(biāo)是greenrobot的EventBus.

EventBus 簡(jiǎn)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(jiǎn)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(biāo)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(cè)事件

EventBus.getDefault().register( this );

取消注冊(cè)

EventBus.getDefault().unregister( this );

發(fā)送數(shù)據(jù)

EventBus.getDefault().post( "我發(fā)射了");

簡(jiǎn)單小例子：使用EventBus傳遞簡(jiǎn)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(cè)
    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(gè)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(cè) , 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(gè)線程發(fā)布出來的，事件處理函數(shù)就會(huì)在這個(gè)線程中運(yùn)行，也就是說發(fā)布事件和接收事件在同一個(gè)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(shí)操作，因?yàn)樗鼤?huì)阻塞事件的傳遞，甚至有可能會(huì)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(gè)線程中發(fā)布出來的，該事件處理函數(shù)都會(huì)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(shí)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(huì)在新的線程中運(yùn)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(jìn)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(gè)線程發(fā)布，該事件處理函數(shù)都會(huì)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(jìn)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(cè)
    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(cè) , 防止Activity內(nèi)存泄漏
    EventBus.getDefault().unregister( this );
  }
}

運(yùn)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(cè)
    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(cè) , 防止Activity內(nèi)存泄漏
    EventBus.getDefault().unregister( this );
  }
}

運(yùn)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(jiǎn)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(cè)

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(cè)

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(cè)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(cè)
    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(cè) , 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(rèn)的線程模型是ThreadMode.POSTING ；默認(rèn)黏性事件為false,也就是默認(rèn)不開啟黏性事件；默認(rèn)的優(yōu)選級(jí)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(gè)單例模式 , 只有一個(gè)實(shí)例對(duì)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(gè)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?jī)?nèi)容了，希望能給大家一個(gè)參考，也希望大家多多支持腳本之家。

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