1. Overview

EventBus definition: it is a publish/subscribe event bus.

In this way, it should contain 4 components: publisher, subscriber, event, and bus.

So what is the relationship between these four?

Obviously: subscribers subscribe to events to the bus, and senders publish events.

The relationship should be roughly like this:

 

Subscribers can subscribe to multiple events, senders can publish any event, and publishers can also be subscribers. To

2. Principle

Execute EventBus.getDefault().register(this) in onCreate; it means that EventBus scans the current class and records all methods starting with onEvent.

How to record it? Use Map, Key as the parameter type of the method, and Value contains our method. So after the execution of onCreate is completed, our onEventMainThread has been stored in EventBus in the form of key-value pairs.

Then when the child thread is executed and EventBus.getDefault().post(Object) is called, EventBus will find the corresponding method in the Map according to the type of the actual parameter in the post, so we find our onEventMainThread, and finally call reflection to execute our way.

3. ThreadMode of EventBus

EventBus contains 4 ThreadMode: PostThread, MainThread, BackgroundThread, Async 

Method name: onEventPostThread, onEventMainThread, onEventBackgroundThread, onEventAsync 

the difference:

OnEventMainThread represents that this method will be executed on the UI thread

OnEventPostThread represents that this method will be executed on the thread where the event is currently posted

The BackgroundThread method, if the event is published in a non-UI thread, it will be executed directly and published in the same thread. If the event is published in the UI thread, it will be added to the background task queue and called one by one using the thread pool.

Async joins the background task queue and uses the thread pool to call. Note that there is no one in the BackgroundThread.

4. Remarks

Note:Almost all EventBus frameworks (EventBus, otto, RxBus), it is not recommended that you register in the parent class, you can only register in the class without subclasses, if you have to Use in BaseActivity, then define an inner class without subclasses in BaseActivity.

Examples are as follows:

public class BaseActivity extend Activity {

      private class EventBusReceiver {
        @Subscribe
        public void onEvnet1(Event1 event) {
            // TODO to do what?
        }
    }
    
    private EventBusReceiver mEventBusReceiver = new EventBusReceiver();
    @Override
    public void onResume() {
        // register event bus
    }
    
    @Override
    public void onPause() {
        // unregister event bus
    }
}