Android design patterns are according to certain well-known practices used repeatedly in developing Android applications. This helps the developers to create applications that can expand, last long, and condense the amount of computational power they use. There are general application frameworks that define its general idea while there are shared programming theories that address some small specific problems related to the code of a given App for example.

Model-View-Controller (MVC):

• Model: The data layer and the business logic are represented by this.
• View: UI components (as well as the presentation layer) constitute this.
• Controller: It deals with user input while also working closely with the model to enhance view aspects.

Model-View-Presenter (MVP):

• Model: Data management along with business logic is being provided by this.
• View: This one would provide an opportunity for the display of data as well as capturing inputs from users.
• Presenter: It’s a mediator between the model and view; it gets updated when a change happens in the model and at the same time handles input from users.

Model-View-ViewModel (MVVM):

• Model: Handles data and business rules.
• View: Renders the data and takes user inputs.
• ViewModel: An intermediary layer that presents data from the model to the view as well as processes user operations

Singleton:

• Make sure that one class has only one instance and give global access to it. Used to manage resources such as database and network connection.

Observer:

• It makes clear that there is a relationship of many objects depending on one another, and if any of them changes state, then all the others are informed and updated instantly. This is used especially when dealing with events and binding data together.

Factory Method:

• It gives us a user interface for generating new entities but allows derivative classes to modify the categories of widgets that will be produced. It helps handle the process of producing an instance without indicating what kind or type of instance it will be.

Dependency Injection:

• A method where an object is given other objects it requires for its functioning. In Android development, frameworks like Dagger or Hilt are often employed as a means of managing dependencies and making code more testable.

Facade:

• This exposes a simple interface to a complicated subsystem thereby making usage easier. In Android development, this can be used to enhance the functionality of APIs and services.

Adapter:

• This modifies the interface of one class into another which the client anticipates. It also allows some classes to work together when they have different interfaces. Frequently utilized in RecyclerView adapters.

Prototype Pattern:

• A prototype is an existing object copied to produce new objects. It is beneficial for creating similar state objects.

Android Design Patterns Implementations

1. MVVM incorporating LiveData and ViewModel:

LiveData: This is the means to hold and manage UI-related data that are mindful of the life cycle.
ViewModel: This is where UI-related data, which do not get destroyed on UI modifications, are kept.

public class MyViewModel extends ViewModel {
private MutableLiveData liveData;

public LiveData<String> getData() {
    if (liveData == null) {
        liveData = new MutableLiveData<>();
        loadData();
    }
    return liveData;
}

private void loadData() {
    // Perform data loading asynchronously
}

}

Repository Pattern:

java
public class UserRepository {
private UserDao userDao;

public UserRepository(UserDao userDao) {
    this.userDao = userDao;
}

public LiveData<User> getUser(int userId) {
    return userDao.getUser(userId);
}

public void insertUser(User user) {
    // Insert user into database
}

}

Dependency Injection with Hilt:

java
@HiltAndroidApp
public class MyApplication extends Application {
}

@Module
@InstallIn(SingletonComponent.class)
public class NetworkModule {
@Provides
public static Retrofit provideRetrofit() {
return new Retrofit.Builder()
.baseUrl(“https://api.example.com”)
.addConverterFactory(GsonConverterFactory.create())
.build();
}
}

Observer Pattern with LiveData:

public class MyActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

    MyViewModel viewModel = new ViewModelProvider(this).get(MyViewModel.class);
    viewModel.getData().observe(this, data -> {
        // Update UI with data
    });
}

}

Factory Pattern for Creating ViewModels:

public class ViewModelFactory implements ViewModelProvider.Factory {
private final Repository repository;

public ViewModelFactory(Repository repository) {
    this.repository = repository;
}

@Override
public <T extends ViewModel> T create(Class<T> modelClass) {
    if (modelClass.isAssignableFrom(MyViewModel.class)) {
        return (T) new MyViewModel(repository);
    }
    throw new IllegalArgumentException("Unknown ViewModel class");
}

}

Frequently Ask Questions