Android Architecture Patterns

Architecture patterns provide a structure that organizes code in a way that's scalable, maintainable, and testable. Over the years, several architecture patterns have emerged in the Android community to tackle the challenges posed by complex app development. Here are the most notable ones:

1. Model-View-Controller (MVC):

Model: Represents the data and business logic.
View: Represents the UI.
Controller: Acts as an interface between Model and View.
However, in Android, Activity or Fragment often takes on the roles of both the View and Controller, which can lead to bloated classes.

2. Model-View-Presenter (MVP):

Model: Represents the data and business logic.
View: Represents the UI and informs the Presenter about user actions.
Presenter: Retrieves the data from the Model, applies the UI logic, and updates the View.
It decouples logic from the Activities and Fragments, leading to more modular and testable code.

3. Model-View-ViewModel (MVVM):

Model: Represents the data and business logic.
View: Represents the UI and observes the ViewModel.
ViewModel: Exposes data streams (typically using Observables) and handles the UI logic.
MVVM is particularly powerful when combined with data-binding, as the UI components in the View can bind directly to properties in the ViewModel.
This architecture is well-suited for Android apps due to its emphasis on a reactive UI, and it's the recommended approach when using the Android Architecture Components.

4. Clean Architecture:

Proposed by Robert C. Martin, it emphasizes the separation of code based on their responsibilities.
The main idea is to split your code into layers, with each layer having a clear responsibility.
- Entity: Contains the business logic.
- Use Cases: Defines actions the user can trigger.
- Interface Adapters: Converts data to a format that can be used by either the entities or the framework-specific code.
- Frameworks and Drivers: Contains all the UI and framework-specific code.
This pattern helps in achieving the separation of concerns and improving testability.

5. Android Architecture Components:

Introduced by Google, these are a set of components that make it easier to design robust, testable, and maintainable apps:

LiveData: An observable data holder.
ViewModel: Designed to store and manage UI-related data.
Room: An SQLite object mapping library.
Data Binding: Allows binding UI components in your layouts directly to data sources.
WorkManager: Manages Android background jobs.
Navigation Component: Simplifies navigation logic implementation.
Lifecycle: Provides components and architectural guidance regarding Android app's lifecycle.

In recent times, the combination of MVVM with Android Architecture Components has been gaining traction due to the official backing by Google and the ease of building scalable and maintainable applications.

When choosing an architecture for an Android application, developers should consider the complexity of their application, their familiarity with the pattern, testability needs, and any existing tools or libraries they plan to use.

Introduction to Android Clean Architecture:
Clean Architecture is a software design philosophy introduced by Robert C. Martin. It promotes separation of concerns and maintainability by organizing code into distinct layers:
- Entities: Contain business logic.
- Use Cases (Interactors): Define application-specific business rules.
- Interface Adapters: Convert data between the use cases and the delivery mechanisms.
- Frameworks and Drivers: Contain delivery mechanisms like UI, databases, and external frameworks.
The goal is to create an architecture that is independent of frameworks and libraries.

The choice depends on factors like testability, ease of maintenance, and project requirements.

Implementing Android Repository pattern:

The Repository pattern is used to separate the logic that retrieves data from the underlying data source (e.g., database, network) from the rest of the application. It provides a clean API for data access. Example code:

public interface UserRepository {
    LiveData<User> getUser();
}

public class UserRepositoryImpl implements UserRepository {
    private UserDao userDao;

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

    @Override
    public LiveData<User> getUser() {
        return userDao.getUser();
    }
}

Android VIPER architecture pattern example:
VIPER (View, Interactor, Presenter, Entity, Router) is an architectural pattern that divides an app into modules with specific responsibilities. Example code:
- View: Displays UI and sends user input to the presenter.
- Interactor: Contains business logic.
- Presenter: Orchestrates the interaction between the view and the interactor.
- Entity: Represents data objects.
- Router: Handles navigation between modules.
VIPER aims to make components more modular and independent.
Choosing the right architecture pattern for Android app:
Choosing the right architecture pattern depends on factors like:
- Project size and complexity.
- Team expertise and familiarity.
- Testability requirements.
- Maintainability goals.
Evaluate MVC, MVP, MVVM, Clean Architecture, or other patterns based on project needs.
Android architecture patterns for scalable apps:
For scalable apps, consider patterns like:
- Clean Architecture: Separation of concerns, testability, and maintainability.
- MVVM: Data binding, ease of testing, and separation of UI logic.
- VIPER: Modular components, scalability, and clear separation of responsibilities.
Architectural patterns that promote separation of concerns and modular design contribute to scalability.