EventBus进阶

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Sticky Events粘性事件

EventBus将某个类型的最后一个粘性事件保留在内存中,也可以将这个粘性事件传递给用户;

不知道写什么栗子,索性举个官方文档的栗子：

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        EventBus.getDefault().postSticky("Hello everyone!");
    }
    @Override
    public void onStart() {
        super.onStart();
        EventBus.getDefault().register(this);
    }

    // UI updates must run on MainThread
    @Subscribe(sticky = true, threadMode = ThreadMode.MAIN)
    public void onEvent(String event) {
        System.out.println("event = " + event);
    }

onCreate在onStart之前运行,在注册时输出上一次粘性事件携带的数据;

打印结果:

04-07 18:24:36.022 20708-20708/com.example.yaoyan.studyeventbus I/System.out: event = Hello everyone!

---

还有另一种更常见的写法：手动获取粘性事件

MessageEvent stickyEvent = EventBus.getDefault().getStickyEvent(MessageEvent.class);
// Better check that an event was actually posted before
if(stickyEvent != null) {
    // "Consume" the sticky event
    EventBus.getDefault().removeStickyEvent(stickyEvent);
    // Now do something with it
}

如果想要移除上一次的粘性事件：

MessageEvent stickyEvent = EventBus.getDefault().removeStickyEvent(MessageEvent.class);

---

Priorities and Event Cancellation优先事件和事件取消

优先级

---

没想到这种东西还真是跟广播很像的呢,也是分优先级的默认是0,数字越大,优先级越高,具体最大能是多少,我觉得没必要研究;

直接上代码(栗子)：

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        EventBus.getDefault().register(this);
    }

    @Subscribe(priority = 2, threadMode = ThreadMode.MAIN)
    public void onEvent2(String event) {
        System.out.println("onEvent2 = " + event);
    }

    @Subscribe(priority = 1, threadMode = ThreadMode.MAIN)
    public void onEvent1(String event) {
        System.out.println("onEvent1 = " + event);
    }


    public void eventBus(View view) {
        EventBus.getDefault().post("hhahahahahah");
    }

    @Subscribe(priority = 3, threadMode = ThreadMode.BACKGROUND)
    public void onEvent3(String event) {
        System.out.println("event3 = " + event);
    }

    @Subscribe(priority = 0, threadMode = ThreadMode.MAIN)
    public void onEvent(String event) {
        System.out.println("event = " + event);
    }

我们可以发现,不是说按照优先级别应该为3-2-1-0么！？

官方文档给我们标注了这样一段话：

==Note: the priority does not affect the order of delivery among subscribers with different ThreadModes!==

也就是说相同ThreadModes模式,才按照优先级,不同的模式就不按照那个规矩;

取消后续订阅者

您可以通过从订阅的事件处理方法调用cancelEventDelivery（Object event）来取消事件传递过程。任何进一步的事件传递将被取消，后续订阅者将不会收到该事件。

// Called in the same thread (default)
@Subscribe
public void onEvent(MessageEvent event){
    // Process the event
    ...
    // Prevent delivery to other subscribers
    EventBus.getDefault().cancelEventDelivery(event) ;
}

Events are usually cancelled by higher priority subscribers. Cancelling is restricted to event handling methods running in posting thread ( ThreadMode.PostThread).

==事件通常被较高优先级的用户取消;必须要在(ThreadMode.PostThread)中运行此事件处理方法;(否则报错)==

AsyncExecutor

---

AsyncExecutor is like a thread pool, but with failure (exception) handling. Failures are thrown exceptions and AsyncExecutor will wrap those exceptions inside an event, which is posted automatically.

Disclaimer: AsyncExecutor is a non-core utility class. It might save you some code with error handling in background threads, but it’s not a core EventBus class.

Usually, you call AsyncExecutor.create() to create an instance and keep it in the Application scope. Then to execute something, implement the RunnableEx interface and pass it to the execute method of AsyncExecutor. Unlike Runnable, RunnableEx may throw an Exception.

If the RunnableEx implementation throws an exception, it will be catched and wrapped into a ThrowableFailureEvent, which will be posted.

If you want to customize your AsyncExecutor instance, call the static method AsyncExecutor.builder(). It will return a builder which lets you customize the EventBus instance, the thread pool, and the class of the failure event.

Another customization option is the execution scope, which gives failure events context information. For example, a failure event may be relevant only to a specific Activity instance or class.

If your custom failure event class implements the HasExecutionScope interface, AsyncExecutor will set the execution scope automatically. Like this, your subscriber can query the failure event for its execution scope and react depending on it.

翻译来自Google翻译:

AsyncExecutor就像一个线程池，但是有失败（异常）处理。 失败引发异常，AsyncExecutor将把这些异常包装在一个自动发布的事件中。

免责声明：AsyncExecutor是一个非核实用类。 它可能会在后台线程中保存一些带有错误处理的代码，但它不是一个核心的EventBus类。

通常，您调用AsyncExecutor.create（）创建一个实例并将其保留在Application范围内。 然后执行某些操作，实现RunnableEx接口并将其传递给AsyncExecutor的execute方法。 与Runnable不同，RunnableEx可能会抛出异常。

如果RunnableEx实现引发异常，它将被捕获并被包装到一个ThrowableFailureEvent中，这将被发布。

如果要自定义AsyncExecutor实例，请调用静态方法AsyncExecutor.builder（）。 它将返回一个构建器，它允许您自定义EventBus实例，线程池和失败事件的类。

另一个自定义选项是执行范围，它提供失败事件上下文信息。 例如，失败事件可能仅与特定的Activity实例或类相关。

如果您的自定义失败事件类实现了HasExecutionScope接口，AsyncExecutor将自动设置执行范围。 像这样，你的订阅者可以查询失败事件的执行范围，并根据它做出反应。

public class MyApplication extends Application {
    @Override
    public void onCreate() {
        super.onCreate();
        System.out.println("MyApplication.onCreate");
        EventBus.getDefault().register(this);

        AsyncExecutor.create().execute(
                new AsyncExecutor.RunnableEx() {
                    @Override
                    public void run() throws LoginException {
                        // No need to catch any Exception (here: LoginException)
                        EventBus.getDefault().postSticky("haha");
                        int a=1/0;
                    }
                }
        );
    }
    @Subscribe(threadMode = ThreadMode.MAIN)
    public void handleLoginEvent(String event) {
        // do something
        System.out.println("handleLoginEvent--event = " + event);
    }

    @Subscribe(threadMode = ThreadMode.MAIN)
    public void handleFailureEvent(ThrowableFailureEvent event) {
        System.out.println("handleFailureEvent---event = " + event.getThrowable().getMessage());
        // do something
    }
}

输出：

04-07 20:00:44.848 31045-31045/com.example.yaoyan.studyeventbus I/System.out: handleLoginEvent--event = haha
04-07 20:00:44.848 31045-31045/com.example.yaoyan.studyeventbus I/System.out: handleFailureEvent---event = divide by zero

参考文献：
EventBus官网