Use EventBus and The Model-View-Presenter pattern to separate concerns and decouple your Android code.

1. EventBus & MVP
The Chocolate & Peanut Butter of Decoupling
Android
By Jim Kirkbride

2. A little bit about myself
Jim Kirkbride
Twitter, github, etc: @jameskbride
Software Craftsman with Pillar Technology
Email: james.kirkbride@gmail.com

3. Why am I giving this
talk?
@jameskbride

4. Android has a lot of
power, but little
direction… @jameskbride

5. …here’s a chainsaw kids, have fun!
@jameskbride

6. ..I’m gonna write an app!
@jameskbride

7. Android is a
“Framework”, not an
“Architecture”
@jameskbride

8. Without architecture this is what you get
@jameskbride

9. Common Android Problems
• The Framework gets in the way
• Making changes is hard
• Testing is painful
• Dealing with lots of nested callbacks
@jameskbride

10. Root Causes
• All of the code lives in Activities and Fragments
• There are no layers, so everything knows about
everything
• Activities and Fragments call up the inheritance chain,
making testing difficult when all code lives there
• Logic is invoked on click listeners and life-cycle methods
@jameskbride

11. Remediations
• Pull as much code as possible out of Activities and
Fragments
• Create layers of abstraction
• Invert Control to Collaborators
• Favor Composition over Inheritance
@jameskbride

12. Let’s look at an example
of what “no architecture”
looks like

13. How do we improve
this?
@jameskbride

14. DecouplingSeparation of Concerns
@jameskbride

15. Separating Concerns
with Model-View-Presenter@jameskbride

16. Separation of Concerns
“In computer science, separation of concerns (SoC) is a
design principle for separating a computer program into
distinct sections, such that each section addresses a
separate concern.”
https://en.wikipedia.org/wiki/Separation_of_concerns @jameskbride

17. This sounds really
familiar…
@jameskbride

18. S
Single Responsibility Principle
OLID
Separation of Concerns
@jameskbride

19. Model View Presenter
@jameskbride

20. @jameskbride

21. Code Time (Finally!)
@jameskbride

22. Implement the Presenter
public class MainActivityPresenter {
MainActivityView view;
public MainActivityPresenter(MainActivityView view) {
this.view = view;
}
public void onNewDataReceived(MyData data) {
view.update(data);
}
}
interface MainActivityView {
void update(MyData data);
}
The View is injected
Presenter only interacts
with the View as an interface
@jameskbride

23. public classs MainActivity extends AppCompatActivity implements
MainActivityView {
MainActivityPresenter presenter;
@Override
public void onCreate(Bundle savedInstance) {
presenter = new MainActivityPresenter(this);
}
@Override
public void update(MyData data) {
//Update the view here
}
}
Implement the View
The Activity implements
the View interface
View method which is
invoked by the presenter
@jameskbride

24. Let’s apply MVP

25. Things to remember
about the View
@jameskbride

26. (Activities || Fragments ||
Custom Layouts) == View
@jameskbride

27. Your View should be
dumb
@jameskbride

28. Presenter View
@jameskbride

29. Decoupling
with EventBus
@jameskbride

30. Coupling
In software engineering, coupling is the degree of
interdependence between software modules; a measure of
how closely connected two routines or modules are; the
strength of the relationships between modules.
https://en.wikipedia.org/wiki/Coupling_(computer_programming) @jameskbride

31. This is a bad thing
because…
@jameskbride

32. Changes in highly-coupled code cause a
ripple effect
@jameskbride

33. Testing becomes harder
@jameskbride

34. How does EventBus
help?
@jameskbride

35. Remember:
Object-Oriented Development
isn’t really about “things”…
@jameskbride

36. It’s about messages
@jameskbride

37. Publisher/Subscriber
@jameskbride

38. Publishing Messages
public class EventBusPublisherDemo {
private EventBus eventBus;
public EventBusPublisherDemo(EventBus eventBus) {
this.eventBus = eventBus;
}
public void update() {
eventBus.post(new MessageEvent());
}
}
@jameskbride

39. public class EventBusSubscriberDemo {
@Subscribe(threadMode = ThreadMode.MAIN)
public void onMessageEvent(MessageEvent event) {/* Do something */};
public void onStart() {
EventBus.getDefault().register(this);
}
public void onStop() {
EventBus.getDefault().unregister(this);
}
public static class MessageEvent { /* Additional fields if needed */
}
}
Subscribing to Messages
@jameskbride

40. Why are you still using
EventBus?
RxJava is the new hotness!
@jameskbride

41. Observer
@jameskbride

42. If your goal is to
decouple your code
Observer won’t help you
@jameskbride

43. Let’s Apply Pub/Sub
with EventBus
@jameskbride

44. Remember that first
slide?
@jameskbride

45. @jameskbride

46. @jameskbride

47. @jameskbride

48. @jameskbride

49. Questions?
@jameskbride

50. Thanks!
@jameskbride

51. References
• Chainsaw: https://pixabay.com/en/log-cutter-wood-cutter-tree-2192640/
• Texas Chainsaw Goat: https://www.flickr.com/photos/noiseprofessor/
13918551433
• Chocolate-Peanut Butter Cheesecake: https://www.flickr.com/photos/
djwtwo/5207974469
• Chocolate02.jpg: https://commons.wikimedia.org/w/index.php?
curid=48897
• Peanut Butter: https://commons.wikimedia.org/wiki/File:PeanutButter.jpg
• Chocolate: https://commons.wikimedia.org/wiki/File:Chocolate(bgFFF).jpg
• Pinky & The Brain: https://www.flickr.com/photos/jdhancock/3725688716

52. References Cont.
• Android Robot: http://www.android.com/branding.html
• Water Drop: https://commons.wikimedia.org/wiki/
File:Ripple_effect_on_water.jpg
• EventBus Publisher/Subscriber: https://github.com/
greenrobot/EventBus/blob/master/EventBus-Publish-
Subscribe.png
• Server is Down: https://www.flickr.com/photos/samazgor/
11807670403

53. Resources
• EventBusMVPDemo Application: https://github.com/
jameskbride/EventBusMVPDemo
• EventBus: http://greenrobot.org/eventbus/
• Model View Presenter Pattern: https://en.wikipedia.org/
wiki/Model%E2%80%93view%E2%80%93presenter

54. Shameless Plug:
Codemash Companion
@jameskbride