GreenRobot-Eventbus

Introduction of EventBus 3.0.0 and its advance features

Transcript

1. GreenRobot - EventBus Himanshu Dudhat
2. What is Eventbus? • An open-source library for Android using the publisher/subscriber pattern for loose coupling. • Enables central communication to decoupled classes with just a few lines of code – simplifying the code, removing dependencies, and speeding up app development
3. How EventBus works? Publisher Event Bus Subscriber Subscriber Event Event Event post() onEvent() onEvent()
4. How to use Eventbus? • Add dependency • Define Events • Define Subscriber • Post Event
5. Add Dependency EventBus is available on JCenter and Maven Central, so just add this dependency to your Gradle script: Current version is : 3.0.0 compile 'org.greenrobot:eventbus:x.x.x'
6. Define Events Events are POJO/Model/Bean without any specific requirements. e.g. public class MessageEvent { public final String message; public MessageEvent(String message) { this.message = message; } }
7. Define Subscribers // This method will be called when a SomeOtherEvent is posted @Subscribe public void handleSomethingElse(SomeOtherEvent event) { doSomethingWith(event); } // This method will be called when a MessageEvent is posted (in the UI thread for Toast) @Subscribe(threadMode = ThreadMode.MAIN) public void onMessageEvent(MessageEvent event) { Toast.makeText(getActivity(), event.message, Toast.LENGTH_SHORT).show(); }
8. Continue… Register Eventbus Unregister Eventbus @Override public void onStart() { super.onStart(); EventBus.getDefault().register(this); } @Override public void onStop() { EventBus.getDefault().unregister(this); super.onStop(); }
9. Post Event That’s it… Time to send event…. EventBus.getDefault().post(new MessageEvent("I want to meet you!"));
10. Advanced features • Sticky Events • Delivery Threads (ThreadMode) • Priorities and Event Cancellation • Configuration
11. Sticky Events • EventBus keeps the last sticky event of a certain type in memory when event posted sticky. • Used to post data even after subscriber unregistered and subscriber registered again • Used to cache data. E.g. sensor data, location data • Sticky event can be delivered to subscribers or queried explicitly.
12. Continue… Way to post sticky event: Consume Sticky Event: EventBus.getDefault().postSticky(new MessageEvent("Hello everyone!")); @Subscribe(sticky = true, threadMode = ThreadMode.MAIN) public void onEvent(MessageEvent event) { // UI updates must run on MainThread textField.setText(event.message); }
13. Getting Sticky event manually: Getting Sticky event manually: Continue… 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 } MessageEvent stickyEvent = EventBus.getDefault().removeStickyEvent(MessageEvent.class); // Better check that an event was actually posted before if(stickyEvent != null) { // Now do something with it }
14. Delivery Threads (ThreadMode) • ThreadMode: POSTING • ThreadMode: MAIN • ThreadMode: BACKGROUND • ThreadMode: ASYNC // Called in the same thread (default) // ThreadMode is optional here @Subscribe(threadMode = ThreadMode.POSTING); // Called in Android UI's main thread @Subscribe(threadMode = ThreadMode.MAIN); // Called in the background thread @Subscribe(threadMode = ThreadMode.BACKGROUND); // Called in a separate thread @Subscribe(threadMode = ThreadMode.ASYNC);
15. Priorities Within the same delivery thread (ThreadMode), higher priority subscribers will receive events before others with a lower priority. Default priority is 0. In different delivery thread priority of delivery will not affect. @Subscribe(priority = 1); public void onEvent(MessageEvent event) { … }
16. Event Cancellation Events are usually cancelled by higher priority subscribers Cancelling is restricted to event handling methods running in posting thread ThreadMode.POST (Default). EventBus.getDefault().cancelEventDelivery(event) ;
17. Configuration EventBusBuilder is used to configure Eventbus Configure the default EventBus instance EventBus eventBus = EventBus.builder().logNoSubscriberMessages(false) .sendNoSubscriberEvent(false).build(); EventBus.builder().throwSubscriberException(BuildConfig.DEBUG) .installDefaultEventBus(); eventInheritance(boolean eventInheritance) executorService(ExecutorService executorService) logNoSubscriberMessages(boolean logNoSubMsg) logSubscriberExceptions(boolean logSubscriberExcp) sendNoSubscriberEvent(boolean sendNoSubEvent) sendSubscriberExceptionEvent(Boolean send) throwSubscriberException(boolean throw)
18. EventBus Features (Summary) • Convenient Annotation based API: Simply put the @Subscribe annotation to your subscriber methods • Thread delivery support: Main(UI), Background, Async • Event & Subscriber inheritance : The OOPs apply to event and subscriber • Zero configuration: Immediately using a default EventBus instance • Configurable: Adjust its behavior using the builder pattern.
19. Pros • Simplifies the communication • Decouples event senders and receivers • Performs well with Activities, Fragments, and background threads • Avoids complex and error-prone dependencies and life cycle issues • Is fast; specifically optimized for high performance
20. Continue… • Is tiny (<50k jar) • Has advanced features like delivery threads, subscriber priorities, etc.
21. Cons • Makes code unreadable and untestable. • You loss control over who’s notifying who unless you use external plugins
22. References http://greenrobot.org/eventbus/ https://github.com/greenrobot/EventBus https://medium.com/@Shyish/eventbus-in-android-lessons-learned-5403747a a3dd
23. Questions?
24. Thanks! +HimanshuDudhat @HimanshuDudhat himanshu.dudhat@gmail.com Team Lead - Android @ Cygnet Infotech Pvt. Ltd. Sr. Software Engineer @ Cygnet Infotech Pvt. Ltd Himanshu Dudhat