Google EventBus 使用详解

大家好，又见面了，我是你们的朋友全栈君。

EventBus是Google.Guava提供的消息发布-订阅类库，它实现了观察者设计模式，消息通知负责人通过EventBus去注册/注销观察者，最后由消息通知负责人给观察者发布消息。

首先使用 maven 依赖：

<!-- https://mvnrepository.com/artifact/com.google.guava/guava -->
        <dependency>
            <groupId>com.google.guava</groupId>
            <artifactId>guava</artifactId>
            <version>19.0</version>
        </dependency>

示例代码：

EventBusCenter.java

package com.lance.google.event.bus;

import com.google.common.eventbus.EventBus;

/**
 * Created by zhangzh on 2017/1/10.
 */
public class EventBusCenter {

    private static EventBus eventBus = new EventBus();

    private EventBusCenter() {

    }

    public static EventBus getInstance() {
        return eventBus;
    }

    public static void register(Object obj) {
        eventBus.register(obj);
    }

    public static void unregister(Object obj) {
        eventBus.unregister(obj);
    }

    public static void post(Object obj) {
        eventBus.post(obj);
    }


}

观察者一

package com.lance.google.event.bus;

import com.google.common.eventbus.Subscribe;

/**
 * Created by zhangzh on 2017/1/10.
 */
public class DataObserver1 {

    /**
     * 只有通过@Subscribe注解的方法才会被注册进EventBus
     * 而且方法有且只能有1个参数
     *
     * @param msg
     */
    @Subscribe
    public void func(String msg) {
        System.out.println("String msg: " + msg);
    }

}

观察者二

package com.lance.google.event.bus;

import com.google.common.eventbus.Subscribe;

/**
 * Created by zhangzh on 2017/1/10.
 */
public class DataObserver2 {
    /**
     * post() 不支持自动装箱功能,只能使用Integer,不能使用int,否则handlersByType的Class会是int而不是Intege
     * 而传入的int msg参数在post(int msg)的时候会被包装成Integer,导致无法匹配到
     */
    @Subscribe
    public void func(Integer msg) {
        System.out.println("Integer msg: " + msg);
    }
}

代码测试

Test.java

package com.lance.google.event.bus;

/**
 * Created by zhangzh on 2017/1/10.
 */
public class Test {

    public static void main(String[] args) throws InterruptedException {

        DataObserver1 observer1 = new DataObserver1();
        DataObserver2 observer2 = new DataObserver2();

        EventBusCenter.register(observer1);
        EventBusCenter.register(observer2);

        System.out.println("============   start  ====================");

        // 只有注册的参数类型为String的方法会被调用
        EventBusCenter.post("post string method");
        EventBusCenter.post(123);

        System.out.println("============ after unregister ============");
        // 注销observer2
        EventBusCenter.unregister(observer2);
        EventBusCenter.post("post string method");
        EventBusCenter.post(123);

        System.out.println("============    end           =============");
    }
}

输出结果:

============   start  ====================
String msg: post string method
Integer msg: 123
============ after unregister ============
String msg: post string method
============    end           =============

看使用起来简单吧!