Android EventBus 3.0.0 使用总结(必看篇)

前言

eventbus框架

eventbus是一个通用的叫法，例如google出品的guava，guava是一个庞大的库，eventbus只是它附带的一个小功能，因此实际项目中使用并不多。用的最多的是greenrobot/eventbus，这个库的优点是接口简洁，集成方便，但是限定了方法名，不支持注解。另一个库square/otto修改自 guava ，用的人也不少。所以今天我们研究的目标是greenrobot的eventbus.

eventbus 简介

1、eventbus3.0.0 是最新的版本。
2、eventbus 是android 发布/订阅事件总线，可简化 activities, fragments, threads, services 等组件间的消息传递。
3、可替代 intent, handler, broadcast ，接口等传统方案，更快，代码更小，50k 左右的 jar 包，代码更优雅，彻底解耦。

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

eventbus原理图

如何添加依赖

在module的build.gredle 文件中的dependencies标签中添加

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

注册事件

eventbus.getdefault().register( this );

取消注册

eventbus.getdefault().unregister( this );

发送数据

eventbus.getdefault().post( "我发射了");

简单小例子：使用eventbus传递简单字符串

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);

    //注册
    eventbus.getdefault().register( this );


    findviewbyid( r.id.button).setonclicklistener(new view.onclicklistener() {
      @override
      public void onclick(view v) {
        eventbus.getdefault().post( "我发射了");
      }
    });
  }

  /**
   * 自定义一个方法 hello() ，用来接收事件。
   * 方法名字可以随便写
   * @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();

    //取消注册 , 防止activity内存泄漏
    eventbus.getdefault().unregister( this );
  }
}

线程模型

在接收事件消息的方法中，可以通过注解的方式设置线程模型，eventbus内置了4中线程模型，分别是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：如果使用事件处理函数指定了线程模型为postthread，那么该事件在哪个线程发布出来的，事件处理函数就会在这个线程中运行，也就是说发布事件和接收事件在同一个线程。在线程模型为postthread的事件处理函数中尽量避免执行耗时操作，因为它会阻塞事件的传递，甚至有可能会引起anr。

mainthread：如果使用事件处理函数指定了线程模型为mainthread，那么不论事件是在哪个线程中发布出来的，该事件处理函数都会在ui线程中执行。该方法可以用来更新ui，但是不能处理耗时操作。

backgroundthread：如果使用事件处理函数指定了线程模型为backgroundthread，那么如果事件是在ui线程中发布出来的，那么该事件处理函数就会在新的线程中运行，如果事件本来就是子线程中发布出来的，那么该事件处理函数直接在发布事件的线程中执行。在此事件处理函数中禁止进行ui更新操作。

async：如果使用事件处理函数指定了线程模型为async，那么无论事件在哪个线程发布，该事件处理函数都会在新建的子线程中执行。同样，此事件处理函数中禁止进行ui更新操作。

小例子1： 在子线程发送数据

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);

    //注册
    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 发射数据线程 : " , thread.currentthread().getname() ) ;
            eventbus.getdefault().post( "我发射了");
          }
        }).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();

    //取消注册 , 防止activity内存泄漏
    eventbus.getdefault().unregister( this );
  }
}

运行结果：

d/event 发射数据线程 :: thread-109
e/event backgroundthread: 消息： 我发射了 thread: thread-109
e/event postthread: 消息： 我发射了 thread: thread-109
e/event async: 消息： 我发射了 thread: pool-1-thread-2
e/event mainthread: 消息： 我发射了 thread: main

小例子2： 在主线程发送数据

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);

    //注册
    eventbus.getdefault().register( this );

    findviewbyid( r.id.button).setonclicklistener(new view.onclicklistener() {
      @override
      public void onclick(view v) {
        log.d( "event 发射数据线程 : " , thread.currentthread().getname() ) ;
        eventbus.getdefault().post( "我发射了");
      }
    });
  }

  @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();

    //取消注册 , 防止activity内存泄漏
    eventbus.getdefault().unregister( this );
  }
}

运行结果：

d/event 发射数据线程 :: main
e/event mainthread: 消息： 我发射了 thread: main
e/event postthread: 消息： 我发射了 thread: main
e/event async: 消息： 我发射了 thread: pool-1-thread-3
e/event backgroundthread: 消息： 我发射了 thread: pool-1-thread-4

黏性事件

除了上面讲的普通事件外，eventbus还支持发送黏性事件。何为黏性事件呢？简单讲，就是在发送事件之后再订阅该事件也能收到该事件，跟黏性广播类似。具体用法如下：

注册

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());
}

取消注册

eventbus.getdefault().unregister( this ) ;

发送事件

eventbus.getdefault().poststicky( "我发射了");

小例子：在mainactivity发送事件，在activity2里注册并且接收事件

mainactivity源码

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 发射数据线程 : " , thread.currentthread().getname() ) ;
        eventbus.getdefault().poststicky( "我发射了");

        startactivity( new intent( mainactivity.this , activity2.class ));
      }
    });
  }
}

activity2源码

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);
    //注册
    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();
    //取消注册 , 防止activity内存泄漏
    eventbus.getdefault().unregister( this ) ;
  }
}

这就是粘性事件，能够收到订阅之前发送的消息。但是它只能收到最新的一次消息，比如说在未订阅之前已经发送了多条黏性消息了，然后再订阅只能收到最近的一条消息。

eventbus源码分析

subscribe 接口源码

@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;
}

可以看出默认的线程模型是threadmode.posting ；默认黏性事件为false,也就是默认不开启黏性事件；默认的优选级为0 。

eventbus 类部分源码

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() 是一个单例模式 , 只有一个实例对象。

threadmode 类源码

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
}

这个类是枚举类，定义了线程模型中的几种类型。

以上这篇android eventbus 3.0.0 使用总结(必看篇)就是小编分享给大家的全部内容了，希望能给大家一个参考，也希望大家多多支持。