Eventbus3.0的使用

簡介

EventBus 是 http://greenrobot.org/ 出的一個 發布者/訂閱者 （ Publisher/Subscriber ）的事件總線。主要是用來在 Android 各個組件之間進行消息傳遞的。能夠很好地對發布者和訂閱者之間進行解耦。

集成

在項目的 build.gradle 文件中添加如下依賴：

compile 'org.greenrobot:eventbus:3.0.0'

使用

發布者Publisher

我們使用EventBus發布消息的時候很方便，只需要一句話就可以。如下：

EventBus.getDefault().post(quot;helloquot;);

在這里我們發布的可以是基本數據類型，可以是字符串，也可以是對象。

訂閱者Subscriber

當我們需要在一個 Activity 或者 Fragment 中訂閱事件時。我們需要注冊 EventBus

EventBus.getDefault().register(this);

當我們注冊了 EventBus 之后我們就需要取消注冊。一般在 Activity 或 Fragment 銷毀的時候注銷。注銷的代碼如下：

EventBus.getDefault().unregister(this);

@Subscriber

當我們注冊了 EventBus 之后。我們就需要寫一個方法。來對事件進行處理。如下：

@Subscribe
    public void test(String strging){
        Log.i(quot;tempquot;,quot;printf quot; string);
    }

在這里。 EventBus 沒有對函數的命進行規定。只需要加上注解 @Subscribe ，方法為 public void 即可。只要方法的參數跟 post 時的類型一致即可接受到改事件。

實例

比如說現在我們有個需求是。點擊一個按鈕就退出應用程序。那么我們使用EventBus可以怎么實現呢？

首先。我們可以在 BaseActivity 中注冊退出應用程序的時間，讓其他的 Activity 都集成該類。

public class BaseActvity extends AppCompatActivity {

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        EventBus.getDefault().register(this);
    }
    @Subscribe
    public void exitApp(ExitApp exitApp){
        finish();
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        EventBus.getDefault().unregister(this);
    }
}

這時候我們只需要在按鈕的點擊時間中發送改消息即可了。

EventBus.getDefault().post(new ExistApp());

事件類 ExistApp 可以隨意，這里只是用來表明語義。

@Subscribe(threadMode = xxx)

• POSTING: Subscriber在發布消息（調用post函數的線程）的線程中執行。

• MAIN: Subscriber將在Android主線程中執行。

• BACKGROUND: Subscriber在后臺線程中執行

• ASYNC: Subscriber在異步線程，也就是在獨立的線程中執行。

優先級

我們可以通過 @Subscribe(priority = 100) 指定一個Subscriber函數的優先級.默認的優先級是0。高優先級的Subscriber將會優先訂閱事件。

@Subscribe(priority = 100)
    public void onEvent(String string){
        Log.i(quot;subscriberquot;,quot;subscriber quot; string);
    }

取消事件分發

在某些情況下，我們不想讓事件被繼續分發了。那么我們就可以在 onEvent (這里的onEvent名稱任意)中取消事件：

@Subscribe(threadMode = ThreadMode.MAIN)
    public void onEvent(String string){
        Log.i(quot;subscriberquot;,quot;subscriber quot; string);
        EventBus.getDefault().cancelEventDelivery(exitApp);
    }

ProGuard

這里參考官方文檔中的代碼： 點我進入官方文檔ProGuard部分

-keepattributes *Annotation*
-keepclassmembers class ** {
    @org.greenrobot.eventbus.Subscribe lt;methodsgt;;
}
-keep enum org.greenrobot.eventbus.ThreadMode { *; }
 
# Only required if you use AsyncExecutor
-keepclassmembers class * extends org.greenrobot.eventbus.util.ThrowableFailureEvent {
    lt;initgt;(java.lang.Throwable);
}

Android Studio插件

參考

/**
 * Each event handler method has a thread mode, which determines in which thread the method is to be called by EventBus.
 * EventBus takes care of threading independently from the posting thread.
 * 
 * @see EventBus#register(Object)
 * @author Markus
 */
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
}