Android MVP (Model View Presenter) pattern and multi-Presenter Activities. Chryssa Aliferi Android Software Engineer ChryssaAliferi 

Our beloved Android 

Our beloved Android: The business logic and UI logic coexist in the Activity classes: 

Our beloved Android: Everything is connected with everything. UI + Business Logic + Data + Multiple Threads = Android GOD Activity 

What is MVP? 

MVP stands for? Most Valuable Player 

MVP stands for? Minimum Viable Product 

What is MVP? Model View Presenter: Separates the presentation layer from the logic. MVP stands for: 

What is MVP? Model View Presenter: MVP stands for: 

What is MVP? Model: is a data layer such as database or a set of classes that provide the data we want to display in the view. View: represents the UI components and transforms the information contained by the model into the UI. Presenter: is a layer that provides View with data from Model, according to some rules. 

MVP Model Model: • Set of classes that define the data. • Business rules for data and data transformations • Data Retrieval 

View: • Activity, Fragment, View, Dialog • Reference to the Presenter • Exposes methods and Events to the presenter • Transforms the information contained by the model into the UI. • Animations • Navigating to other screens MVP View 

Presenter: • Middle man between View and Model • Controls and updates UI • Handles all UI events on behalf of the view • Retrieves data from the Model layer and displays them in the View MVP Presenter 

How to implement MVP? 

• View interface - “Screen” • all “Screen” methods refer to view behaviour • Android Activity • “screen” methods implemented • Presenter class & Presenter “children” flows • accesses view through screen MVP Implementation 

MVP Example A new screen concerning the Payment feature, with two modes:
 • Select Payment • Edit Payment 

PaymentActivity Without MVP: 

PaymentScreen.java interface: 

PaymentActivity With MVP: 

PaymentPresenter.java: 

MVP Example What about multi- Presenter Activities? Let’s try this again… 

PaymentScreen.java interface: 

PaymentActivity with multiple presenters: 

PaymentPresenter with multiple presenters: 

EditPaymentFlow.java : 

SelectPaymentFlow.java : 

Taxibeat MVP Example The Taxibeat PaymentMeans Activity Case. 

Taxibeat PaymentActivity.java : 

Taxibeat MVP Example Another Taxibeat case: Multi-Presenter Activities 

Taxibeat LocateActivity.java: • LocateActivity.java is the Main Taxibeat Activity • LocateActivity.java contains 2 basic Presenters, the LocatePresenter.java and the MenuPresenter.java • LocatePresenter.java has 3 presenter flow descendants, the PickupFlow.java, the DropOffFlow.java and the CallingFlow.java 

PickupFlow.java • LocatePresenter.java descendant • PickupFlow.java presenter contains all the logic behind the process of setting the correct pickup location. • onAddressAnimationEnd(), PickupFlow calls “destroys” itself and gives control to DropOffFlow. • onBackButton() press we terminate the app. 

DropOffFlow.java • LocatePresenter.java descendant • DropOffFlow.java presenter contains all the logic behind the process of setting the dropoff location and all the hailing options. • onClick() of the green button, DropOffFlow “destroys” itself and gives control to CallingFlow. • onBackButton() press we handle back control to the PickupFlow. 

CallingFlow.java • LocatePresenter.java descendant • CallingFlow presenter contains all the logic behind the process of calling a taxi. • onClick() of the red button or on onBackButton() press, CallingFlow “destroys” itself • Then gives control back to DropOffFlow. 

MenuPresenter.java • MenuPresenter presenter contains all the logic behind the menu initialisation and menu onClick actions. • MenuPresenter is an autonomous presenter that handles only menu actions. 

LocateActivity contains: LocatePresenter MenuPresenter PickupFlow CallingFlow DropOffFlow MenuScreen LocateScreen 

MVP Recap 

MVP Pros vs Cons Pros: • Separation of concerns • Maintainability • Re-usability of views, presenters and screens • Less time spending on view control • Information hiding • Testable! Cons: • Redundancy • Learning curve • Takes time, not suitable for small projects. 

MVP Do not forget: • Use your logic, to distinguish the main business flows • Create your “Screen”, your View interface • Activities, Fragments or custom views implement the View interface • Separate your app business logic by moving it to a plain java Presenter object • Make Presenter “children” if needed to make your code even cleaner • Spend time writing a clean interface between your Presenter and your View • Test your Presenter. • Retain the state of the Presenters, “initialise” and “destroy” them. 

§ GitHub Project https://github.com/ChryssaAliferi/MultiPresenterMVP 

The End! Any Questions? 

www.taxibeat.com/careers We are hiring! 

Resources: • Is Activity GOD? by Kenju Wagatsuma on SlideShare • MVP design pattern for Android Apps by Infinum on SlideShare • Android Code That Scales, With MVP by Nathan Barraille • MVP for Android: how to organize the presentation layer by Antonio Leiva • Introduction to Model View Presenter on Android by Konstantin Mikheev 

§ Thank you! Chryssa Aliferi Android Software Engineer ChryssaAliferi