What I learnt using the Presenter Pattern

Given at Oredev 2016: https://vimeo.com/191068122

Patterns of yore like MVP, MVVM etc. have taken the Android world by storm these days. These are not new concepts per say, but their application to the world of mobile development is new.

In this talk, I share some of the learnings from having adopted this pattern in an actual production application.

What are the common patterns used in mobile these days? What are the problems with adoption? What are the advantages of adoption? How do we adopt these patterns in a way that doesn't lead to death by abstraction?

We'll discuss the juicy learnings from war stories in this session.

Transcript

1. What I learnt using the 
 Presenter Pattern
2. Know thy pattern Primer on MVC, MVP, MVVM
3. Know thy patterns View Controller Model user events modifies fire state change events MVC
4. Know thy patterns MVP View Presenter Model User interaction user events modifies fire state change events updates
5. View Presenter Model User interaction user events modifies fire state change events updates Know thy patterns MVP Passive
6. View Model User interaction Know thy patterns MVP user events modifies updates Supervising
 Controller Data Binding
7. View Model Know thy patterns MVVM Data Binding View Model update state fire state change (view queries VM again) (Presentation Model)
8. MVVM MVC MVP View Controller Model user events modifies state change events View Presenter Model User interaction user events modifies state change events updates View Model View Model modifies state changes Know thy patterns Data Binding
9. Evolve a Pattern "Architecture changes" are painful Introducing patterns is awesome
10. Evolve a Pattern class Customer {
 String dateOfBirth; String fullName; } "Bruce Lee" "1940-11-27" Don't add to the Model! Create a ViewModel class CustomerViewModel {
 Customer user;
 
 CustomerViewModel(Customer user) {
 this.user = user;
 }
 
 boolean canPurchaseAlcohol() {
 // return age() > 18;
 }
 
 String getInitials() {
 // return strip(user.fullName);
 }
 }
11. Don't use terms interchangeably ! ViewModel != Presenter
12. Don't use terms interchangeably Model Database structure or
 mirror of REST JSON Model decorates View Model
13. Don't use terms interchangeably Activities Fragments Views decorates Presenters Model decorates View Model ! Model
14. Where to put the Presenter? ¯\_(ϑ)_/¯
15. Where to put the Presenter? Activity Fragment Fragment ListView Adapter ViewHolder ViewHolder View ActivityPresenter? FragmentPresenter? ListViewPresenter? AdapterPresenter? ViewHolderPresenter? ViewPresenter?
16. Where to put the Presenter? Activity Fragment Fragment ListView Adapter ViewHolder ViewHolder View ActivityPresenter? FragmentPresenter? ListViewPresenter? AdapterPresenter? ViewHolderPresenter? ViewPresenter?
17. Death by Boilerplate :(
18. Use some form of DataBinding! Death by Boilerplate EventBus(es) So how does one combat the Boilerplate? Use some form of DataBinding! EventBus(es)
19. CheckoutActivity CheckoutActivityPresenter CheckoutAPresenterView Interface cause Java! CheckoutAdapter PaymentCardViewHolder AdapterPresenter PaymentCardVHPresenter AdapterPresenterView VHPresenterView implements new (View activity) { mView = activity; } CheckoutActivityPresenter AdapterPresenter new (View adapter) { mView = adapter; } mCheckoutActivityPresenter mAdapterPresenter Death by Boilerplate
20. CheckoutActivity CheckoutActivityPresenter CheckoutAPresenterView CheckoutAdapter PaymentCardViewHolder AdapterPresenter PaymentCardVHPresenter AdapterPresenterView VHPresenterView new (View activity) { mView = activity; } CheckoutActivityPresenter AdapterPresenter Button.onClick(event) new (View adapter) { mView = adapter; } mCheckoutActivityPresenter mAdapterPresenter launchPaymentActivity() Death by Boilerplate
21. CheckoutActivity CheckoutActivityPresenter CheckoutAPresenterView CheckoutAdapter PaymentCardViewHolder AdapterPresenter PaymentCardVHPresenter AdapterPresenterView VHPresenterView new (View activity) { mView = activity; } CheckoutActivityPresenter AdapterPresenter Button.onClick(event) new (View adapter) { mView = adapter; } mCheckoutActivityPresenter mAdapterPresenter launchPaymentActivity() OR ...... use an EventBus Death by Boilerplate
22. CheckoutActivity CheckoutActivityPresenter CheckoutAPresenterView CheckoutAdapter PaymentCardViewHolder AdapterPresenter PaymentCardVHPresenter Death by Boilerplate (Event Bus) AdapterPresenterView VHPresenterView new (View activity) { mView = activity; } Button.onClick(event) new (View adapter) { mView = adapter; } mCheckoutActivityPresenter mAdapterPresenter launchPaymentActivity() bus.post(event) @Subscribe
23. Compose Presenters ¯\_ + _/¯
24. Compose Presenters
25. Reinforce reasons for pattern
26. (Unit) Testing is faster and easier*
27. ...But UI testing exists
28. ✌ fragmentedpodcast.com tech.instacart.com @kaushikgopal kaush.co My thanks to @cyrilmotier who graciously allowed me to rip-off his slide deck theme