Modern Ways to Architect your Android app: MVP and MVVM

Hello! I am Jorge Coca Mobile Engineer @ SPR Consulting. You can find me at: @jcocaramos

What does MVP stand for? Model View Presenter

What does MVVM stand for? Model View-View Model

Why do I need to learn both?

“ During the last years, the community seemed to be inclined to incorporate MVP patterns in their Android apps

“ … but then, during the last Google IO

DATA BINDING Connects data and UI elements -> Automates listener creation, message sending, setters...

What’s the goal of these two approaches?

We want to make our code... ■ Independent of frameworks ■ Testable ■ Independent of UI ■ Independent of storage mechanisms ■ Independent of external dependencies

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Model View Presenter

Model View Presenter (MVP) ■ Derivation of MVC pattern ■ Mostly used for UI interfaces ■ Main problem that solves is testing Model Presenter View

View Presenter Model 1 User does something 2 Gets data 3 Prepares and returns data 4 Updates view

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M for Model ■ Domain object ■ Holds data, but not behaviors ■ It may contain validation, but never formatting ■ POJO objects

V for View ■ Displays the data ■ Routes commands to the presenter ■ It’s going to be abstracted using an interface implemented by Android components ■ It’s passive ○ Activities and Fragments

P for Presenter ■ Acts upon the model and the view ■ Receives commands from the view and responds accordingly ■ Responsible for formatting data ■ Responsible for presentation logic ■ Doesn’t have Android dependencies ○ GOOD: unit tests ○ BAD: attached to View lifecycle

GOOD Test all our UI code without framework code

BAD Attached to View lifecycle

Model View-View Model

Model View-View Model (MVVM) ■ Commonly used by Microsoft ■ Binding engine will avoid boilerplate code View Model State and operations View Model Data binding and commands Sends notification ViewModel updates the model Sends notification

VM for View-Model ■ ViewModel implementations will contain state logic of the view ■ Activities and Fragments lifecycle tied to VM (that’s why DataBinding is good!)

VM for View-Model ■ ViewModel won’t contain a view instance; will use events mechanisms ■ Decouple our Views from the Model by introducing a ViewModel layer ■ Don’t tie directly to Domain models; create a POJO for the binding

V for View ■ Views will keep an instance of the ViewModel and will register different listeners to know when the ViewModel has changed

… but what is really Data Binding?

“ Data Binding is the process that establishes a connection between the application UI and the Business logic. If the settings and notifications are correctly set, the data reflects changes when made. It can also mean then when the UI is changed, the underlying data will reflect that change.

“ Data Binding is the process that establishes a connection between the application UI and the Business logic. If the settings and notifications are correctly set, the data reflects changes when made. It can also mean then when the UI is changed, the underlying data will reflect that change.

MVVM with Data Binding - Layouts

MVVM with Data Binding - Layouts

MVVM with Data Binding - Layouts

MVVM with Data Binding - Layouts

MVVM with Data Binding - ViewModel public class ContactViewModel extends BaseObservable { private String mContactName; // Constructors and other things omitted for clarity. @Bindable public String getName() { return mContactName; } public void setName(String name) { mContactName = name; notifyPropertyChanged(BR.name); } }

BaseObservable ■ Provides the infrastructure for setting up the data binding process ■ BR class is generated: ○ Each POJO field adorned with @Bindable will have a constant declared in BR corresponding to the name

MVVMwith DataBiding - Establish the binding public class AddNewContactActivity extends Activity{ private ContactViewModel mViewModel; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); mViewModel = createViewModel(); initializeViewModel(); } private void ContactViewModel createViewModel() { ... } private void initializeViewModel() { ActivityAddNewContactBinding binding = DataBindingUtil.setContentView(this, R.layout.activity_add_new_contact); binding.setContact(mViewModel); } // Rest of the code omitted. }

MVVMwith DataBiding - Establish the binding public class AddNewContactActivity extends Activity{ private ContactViewModel mViewModel; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); mViewModel = createViewModel(); initializeViewModel(); } private void ContactViewModel createViewModel() { ... } private void initializeViewModel() { ActivityAddNewContactBinding binding = DataBindingUtil.setContentView(this, R.layout.activity_add_new_contact); binding.setContact(mViewModel); } // Rest of the code omitted. }

What’s the current status of Data Binding?

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Data Binding - Current Status https://developer.android.com/tools/data-binding/guide.html ■ Lots of bugs ■ Not even all the examples work ■ It can cause errors even in snippets where you don’t use data binding

Don’t use data binding in production!

Example

Rock Hall Of Fame MVP RecyclerView with a list of rock bands implemented using MVP

Band details Mix of MVP with data binding Example of how data binding works and its current status Place your screenshot here

Links ■ Github repo with the example ○ https://github.com/jorgecoca/RockHallOfFameMVP ■ Slides ○ https://speakerdeck.com/jorgecoca/modern-ways-to- architecture-your-android-app-mvp-and-mvvm

Thank you!