The Evolution of MV Patterns in Android: A Journey Through Code

Introduction

The Android platform has witnessed a remarkable evolution in terms of design patterns used to develop robust and maintainable applications. One of the pivotal aspects of Android development is the organization of code to ensure scalability, readability, and maintainability. Over the years, several architectural patterns have emerged, and the Model-View (MV) pattern is at the core of Android app development. In this article, we will explore the evolution of MV patterns in Android, with coding examples illustrating each phase of its development.

I. Model-View-Controller (MVC)

In the early days of Android development, the Model-View-Controller (MVC) pattern was the de facto choice for organizing code. It was simple and separated an application into three components:

Model: Represented the data and business logic.
View: Responsible for rendering the user interface.
Controller: Managed user input and handled communication between the Model and View.

Let’s take a look at a basic example of MVC in Android:

java

// Model

public class User {

private String name;

public User(String name) {
this.name = name;
}public String getName() {
return name;
}
}// View
public class MainActivity extends AppCompatActivity {
private TextView usernameTextView;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
usernameTextView = findViewById(R.id.usernameTextView);
}

public void displayUsername(User user) {
usernameTextView.setText(user.getName());
}
}

// Controller
public class UserController {
private User user;
private MainActivity view;

public UserController(MainActivity view) {
this.view = view;
this.user = new User(“John Doe”);
}

public void updateUser() {
view.displayUsername(user);
}
}

This pattern helped separate concerns but had its drawbacks, such as the tight coupling between the Controller and View.

II. Model-View-Presenter (MVP)

As Android development matured, the Model-View-Presenter (MVP) pattern emerged as a response to MVC’s issues. MVP sought to improve testability and separation of concerns by introducing the Presenter:

Model: Remained responsible for data and business logic.
View: Focused solely on UI rendering and user input handling.
Presenter: Acted as a mediator between the Model and View.

Here’s a code example illustrating the MVP pattern in Android:

java

// Model (same as in MVC)

// View
public interface MainView {
void displayUsername(String username);
}

public class MainActivity extends AppCompatActivity implements MainView {
private TextView usernameTextView;
private MainPresenter presenter;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
usernameTextView = findViewById(R.id.usernameTextView);
presenter = new MainPresenter(this);
}

@Override
public void displayUsername(String username) {
usernameTextView.setText(username);
}
}

// Presenter
public class MainPresenter {
private User user;
private MainView view;

public MainPresenter(MainView view) {
this.view = view;
this.user = new User(“John Doe”);
}

public void updateUser() {
view.displayUsername(user.getName());
}
}

MVP improved testability by separating the UI logic into the Presenter and allowed for better code organization. However, it still had some shortcomings, including complex interfaces and a one-to-one relationship between Views and Presenters.

III. Model-View-ViewModel (MVVM)

The Model-View-ViewModel (MVVM) pattern became popular with the rise of data-binding libraries like Android Data Binding and LiveData. MVVM aimed to simplify UI logic further and provide a more robust and flexible architecture:

Model: Unchanged, handling data and business logic.
View: Remained responsible for UI rendering.
ViewModel: Introduced as a mediator between the Model and View, responsible for preparing data for the View.

Let’s explore the MVVM pattern in Android:

java

// Model (same as in previous examples)

// ViewModel
public class MainViewModel extends ViewModel {
private MutableLiveData<String> usernameLiveData = new MutableLiveData<>();
private User user;

public MainViewModel() {
this.user = new User(“John Doe”);
usernameLiveData.setValue(user.getName());
}

public LiveData<String> getUsernameLiveData() {
return usernameLiveData;
}
}

// View
public class MainActivity extends AppCompatActivity {
private TextView usernameTextView;
private MainViewModel viewModel;

viewModel.getUsernameLiveData().observe(this, new Observer<String>() {
@Override
public void onChanged(String username) {
usernameTextView.setText(username);
}
});
}
}

MVVM introduced data-binding capabilities and simplified UI updates through LiveData. It encouraged a more declarative approach to UI design, reducing boilerplate code.

IV. Model-View-Intent (MVI)

In recent years, the Model-View-Intent (MVI) pattern has gained popularity, especially in combination with libraries like RxJava and Kotlin Flow. MVI embraces a unidirectional data flow:

Model: Remains responsible for data and business logic.
View: Renders the UI and sends user intents to the ViewModel.
Intent: Represents user actions.
ViewModel: Manages the application’s state and business logic, responding to user intents and updating the Model.

Here’s a code example illustrating the MVI pattern:

java

// Model (same as in previous examples)

// Intent
public sealed interface MainIntent {
object LoadData : MainIntent()
data class UpdateUsername(val username: String) : MainIntent()
}

// ViewModel
public class MainViewModel : ViewModel() {
private val _state = MutableLiveData<String>()
val state: LiveData<String> = _state

fun processIntent(intent: MainIntent) {
when (intent) {
is MainIntent.LoadData -> loadData()
is MainIntent.UpdateUsername -> updateUsername(intent.username)
}
}

private fun loadData() {
// Fetch data from Model and update state
val user = User(“John Doe”)
_state.value = user.getName()
}

private fun updateUsername(username: String) {
// Update user data in Model and update state
val user = User(username)
_state.value = user.getName()
}
}

// View
public class MainActivity : AppCompatActivity() {
private lateinit var usernameTextView: TextView
private lateinit var viewModel: MainViewModel

override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
usernameTextView = findViewById(R.id.usernameTextView)
viewModel = ViewModelProvider(this).get(MainViewModel::class.java)

// Send intent to load data
viewModel.processIntent(MainIntent.LoadData)

viewModel.state.observe(this, { username ->
// Update UI with the latest state
usernameTextView.text = username
})
}
}

MVI enforces a strict unidirectional data flow, making it easier to reason about the application’s behavior and handle complex UI interactions.

Conclusion

The Android platform has evolved significantly in terms of architectural patterns for organizing code. From the traditional Model-View-Controller (MVC) pattern to the modern Model-View-Intent (MVI) pattern, developers have had various options to choose from based on their project’s needs and requirements.

Understanding the evolution of these MV patterns is essential for Android developers to make informed decisions about the architecture of their applications. Each pattern introduced improvements and addressed shortcomings, leading to more efficient and maintainable Android apps.

As the Android ecosystem continues to evolve, it’s crucial for developers to stay up-to-date with the latest trends and patterns, ensuring that their applications remain scalable, robust, and easy to maintain in the ever-changing landscape of mobile development.