Decoupled android app communication with EventBus

Rashi Karanpuria

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Apr 12, 2017 · 2 min read

While creating an app which had a lot of in app communication in use, I used broadcast receivers with bundles and parcelables. It quickly grew into a lot of code which was tightly coupled and hard to keep track of. Not to mention the time spent removing error cases due to activity and fragment lifecycle events.
So I decided to find a better way out for this, I came across a post about loose coupled in app communication using EventBus and I decided to give it try.

EventBus is an open-source library for Android using the publisher/subscriber pattern for loose coupling.

The event bus :
• simplifies the communication between app components.
• decouples event senders and receivers.
• helps avoid complex and error-prone dependencies and life cycle issues in activities & fragments.
• can be used with services. Awesome!
• makes your code super simple.
• is a tiny library which is way faster.
• has advanced features like delivery threads, subscriber priorities, etc.

Wait, there is more:
• annotation based api.
• Main and background thread delivery.
• event and subscriber inheritance.
• configurable to your requirements.
• sticky events.

And after you are all impressed and ready to move to the first tutorial you can put your hands on, hold on it just takes 3 steps.

1. Define events:

public class LocationEvent {    Location location;    public LocationEvent(Location location) {
        this.location = location;
    }    public Location getLocation() {
       return location;
    }
}

2. Prepare subscribers: Declare and annotate your subscribing method, optionally specify a thread mode:

@Subscribe
public void onLocationEvent(LocationEvent event) {
    /* Do what you need to */
};

Register and unregister your subscriber. For example in an Activity (depends on component lifecycle):

@Override
 public void onStart() {
     super.onStart();
     EventBus.getDefault().register(this);
 }@Override
 public void onStop() {
     super.onStop();
     EventBus.getDefault().unregister(this);
 }

You can use a singleton Eventbus too.

3. Post events:

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

So here is a link to the EventBus’s github library : https://github.com/greenrobot/EventBus

Hope you are little excited about loose coupling and simpler in-app communication in Android. If you have any suggestion, question, or you would like to add something, just type it out in comments below!

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