EventBus

EventBus is a publish/subscribe event bus for Android and Java.

EventBus…

simplifies the communication between components
- decouples event senders and receivers
- performs well with Activities, Fragments, and background threads
- avoids complex and error-prone dependencies and life cycle issues
makes your code simpler
is fast
is tiny (~60k jar)
is proven in practice by apps with 1,000,000,000+ installs
has advanced features like delivery threads, subscriber priorities, etc.

EventBus in 3 steps

Define events:

public static class MessageEvent { /* Additional fields if needed */ }

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

@Subscribe(threadMode = ThreadMode.MAIN)  
public void onMessageEvent(MessageEvent event) {
    // Do something
}

Register and unregister your subscriber. For example on Android, activities and fragments should usually register according to their life cycle:

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

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

Post events:

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

Read the full getting started guide.

There are also some examples.

Note: we highly recommend the EventBus annotation processor with its subscriber index. This will avoid some reflection related problems seen in the wild.

Add EventBus to your project

Available on Maven Central.

Android projects:

implementation("org.greenrobot:eventbus:3.3.1")

Java projects:

implementation("org.greenrobot:eventbus-java:3.3.1")

<dependency>
    <groupId>org.greenrobot</groupId>
    <artifactId>eventbus-java</artifactId>
    <version>3.3.1</version>
</dependency>

R8, ProGuard

If your project uses R8 or ProGuard this library ships with embedded rules.

Homepage, Documentation, Links

For more details please check the EventBus website. Here are some direct links you may find useful:

License

EventBus binaries and source code can be used according to the Apache License, Version 2.0.

Other projects by greenrobot

ObjectBox (GitHub) is a new superfast object-oriented database.

Essentials is a set of utility classes and hash functions for Android & Java projects.