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
   

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2. Know thy pattern
   Primer on MVC, MVP, MVVM
   

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3. Know thy patterns
   View
   Controller
   Model
   user events
   modifies
   fire
   state change
   events
   MVC
   

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4. Know thy patterns
   MVP
   View
   Presenter
   Model
   User interaction
   user events
   modifies
   fire
   state change events
   updates
   

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5. View
   Presenter
   Model
   User interaction
   user events
   modifies
   fire
   state change events
   updates
   Know thy patterns
   MVP
   Passive
   

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6. View
   Model
   User interaction
   Know thy patterns
   MVP
   user events
   modifies
   updates
   Supervising

   Controller
   Data
   Binding
   

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7. View
   Model
   Know thy patterns
   MVVM
   Data
   Binding
   View Model
   update state
   fire state change
   (view queries VM again)
   (Presentation Model)
   

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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
   

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9. Evolve a Pattern
   "Architecture changes" are painful
   Introducing patterns is awesome
   

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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);

    }

    }
    

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11. Don't use terms
    interchangeably !
    ViewModel != Presenter
    

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12. Don't use terms interchangeably
    Model
    Database structure
    or

    mirror of REST JSON
    Model
    decorates
    View Model
    

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13. Don't use terms interchangeably
    Activities
    Fragments
    Views
    decorates
    Presenters
    Model
    decorates
    View Model
    ! Model
    

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14. Where to put the
    Presenter?
    ¯\_(ϑ)_/¯
    

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15. Where to put the Presenter?
    Activity
    Fragment
    Fragment
    ListView
    Adapter
    ViewHolder
    ViewHolder
    View
    ActivityPresenter?
    FragmentPresenter?
    ListViewPresenter?
    AdapterPresenter?
    ViewHolderPresenter?
    ViewPresenter?
    

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16. Where to put the Presenter?
    Activity
    Fragment
    Fragment
    ListView
    Adapter
    ViewHolder
    ViewHolder
    View
    ActivityPresenter?
    FragmentPresenter?
    ListViewPresenter?
    AdapterPresenter?
    ViewHolderPresenter?
    ViewPresenter?
    

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17. Death by Boilerplate
    :(
    

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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)
    

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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
    

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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
    

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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
    

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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
    

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23. Compose Presenters
    ¯\_ + _/¯
    

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24. Compose Presenters
    

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25. Reinforce reasons
    for pattern
    
    

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26. (Unit) Testing is faster and easier*
    

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27. ...But UI testing exists
    

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28. ✌
    fragmentedpodcast.com
    tech.instacart.com
    @kaushikgopal
    kaush.co
    My thanks to @cyrilmotier
    who graciously allowed me to rip-off his slide deck theme
    

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