频道栏目
首页 > 程序开发 > 移动开发 > 其他 > 正文
EventBus 3.0.0使用总结
2017-04-17 09:48:42         来源:weixin_35791555的博客  
收藏   我要投稿

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。

EventBus原理图

这里写图片描述

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 );

}

}

效果图

这里写图片描述

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。

点击复制链接 与好友分享!回本站首页
上一篇:关于TotoiseSVN版本控制工具的使用
下一篇:第4章 view的工作原理
相关文章
图文推荐
点击排行

关于我们 | 联系我们 | 广告服务 | 投资合作 | 版权申明 | 在线帮助 | 网站地图 | 作品发布 | Vip技术培训 | 举报中心

版权所有: 红黑联盟--致力于做实用的IT技术学习网站