Google eventbus usage details

Hello everyone , I meet you again , I'm your friend, Quan Jun .

EventBus yes Google.Guava News release - Subscription class library , It implements the observer design pattern , Inform the person in charge of the message through EventBus To register / Log off the observer , In the end, the person in charge of the information informs the observer to release the information .

use first maven rely on ：

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

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Sample code ：

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);
    }


}

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Observer one

package com.lance.google.event.bus;

import com.google.common.eventbus.Subscribe;

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

    /**
     *  Only through @Subscribe The annotated method will be registered in EventBus
     *  And there are and only can be 1 Parameters 
     *
     * @param msg
     */
    @Subscribe
    public void func(String msg) {
        System.out.println("String msg: " + msg);
    }

}

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Observer 2

package com.lance.google.event.bus;

import com.google.common.eventbus.Subscribe;

/**
 * Created by zhangzh on 2017/1/10.
 */
public class DataObserver2 {
    /**
     * post()  Auto boxing is not supported , Only use Integer, Out of commission int, otherwise handlersByType Of Class Would be int instead of Intege
     *  And the incoming int msg Parameter in post(int msg) It's packaged as Integer, Cause can't match to 
     */
    @Subscribe
    public void func(Integer msg) {
        System.out.println("Integer msg: " + msg);
    }
}

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Code testing

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  ====================");

        //  Only registered parameter types are String The method of will be called 
        EventBusCenter.post("post string method");
        EventBusCenter.post(123);

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

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

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Output results :

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

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It looks simple to use !

EventBus Attention to the use of ：

1. Code readability is poor , When used in projects , from post The place of , Inquire about handle Use , Is to use ide Search services for , The problem is hard to locate , It's not as easy to query as ordinary interface calls ;

2. because EventBus Put the message queue into memory ,listener Consume this message queue , So after the system restarts , Messages saved or piled up in the queue are lost .

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