Build Android applications using MVVM and Clean Architecture

Designing a robust and maintainable architecture is critical in the world of Android development. Two popular architectural patterns, Model-View-ViewModel (MVVM) and Clean Architecture, provide a structured approach to building Android applications. In this article, we'll explore how to combine these two patterns to create scalable and testable Android applications.

1. Understand MVVM: The Model-View-ViewModel (MVVM) pattern separates the concerns of data management, UI rendering, and user interaction. It consists of the following components:

• Model: Represents the data and business logic of the application.

• View: Displays UI elements and interacts with the user.

• ViewModel: Between the model and the view, providing data for the UI and handling user actions.
  2. Advantages of MVVM: MVVM offers several advantages, including:

• Separation of Concerns: The separation of UI logic and business logic enhances maintainability.

• Testability: ViewModel and Model classes can be easily unit tested without depending on the Android framework.

• Lifecycle awareness: MVVM leverages LiveData or RxJava to handle data updates and lifecycle events.
  3. Understand Clean Architecture: Clean Architecture emphasizes separation of concerns and dependency inversion. It consists of three layers:

• Presentation Layer: Handles UI-related tasks and interacts with the ViewModel.
• Domain Layer: Contains framework-independent business logic and use cases.
• Data Layer: Manages data retrieval and storage, including local and remote data sources.

4.Combining MVVM with Clean Architecture: To combine MVVM with Clean Architecture in Android, we can follow the following guidelines:

• UI layer: Implement the View and ViewModel components of MVVM. View observes LiveData or RxJava stream provided by ViewModel.
• Presentation layer: Create ViewModel classes that handle UI-related tasks and communicate with the domain layer.
• Domain Layer: Defines use cases and business logic independent of the Android framework. Use interfaces to decouple layers.
• Data Layer: A repository that implements abstract data sources (local databases, remote APIs). Use dependency inversion to make the domain layer independent of the concrete implementation.

5. Benefits of MVVM with Clean Architecture: By combining MVVM with Clean Architecture, we can achieve the following benefits:

• Separation of concerns: Each layer has distinct responsibilities, improving maintainability and modularity.
• Testability: Business logic and use cases can be tested independently of the UI, resulting in more reliable code.
• Extensibility: The architecture allows for easy expansion and modification without affecting other layers.
• Reusability: The domain layer is independent of the framework and can be reused on different platforms.

6. Implementing MVVM with Clean Architecture in Android: Provides step-by-step instructions on how to implement MVVM with Clean Architecture in Android projects. Includes code snippets, best practices, and recommended libraries (eg, LiveData, Room, Retrofit) for each layer.

7. Conclusion: MVVM with Clean Architecture provides a powerful approach to building modular, testable and maintainable Android applications. By separating concerns and taking advantage of the strengths of each pattern, developers can create powerful applications that are easily extensible and adaptable.

Conclusion: Understanding the MVVM pattern and Clean Architecture is critical for Android developers seeking to build high-quality applications. By combining these patterns, developers can take advantage of both and create well-structured, scalable, and maintainable Android applications.

certainly! Here are some examples to illustrate the implementation of MVVM using Clean Architecture in Android:

UI layer (View and ViewModel): In the UI layer, you typically have activities or fragments as views and corresponding ViewModel classes. Here's an example of a simple login screen:

// LoginActivity.kt (View) 
class  LoginActivity : AppCompatActivity () { 
    private  lateinit  var viewModel: LoginViewModel 

    override  fun  onCreate (savedInstanceState: Bundle ?) { 
        super .onCreate(savedInstanceState) 
        setContentView(R.layout.activity_login) 

        viewModel = ViewModelProvider( this ). get (LoginViewModel:: class .java) 

        // 从 ViewModel 观察 LiveData
         viewModel.getLoginResult().observe( this , { loginResult ->
            // 根据登录结果更新 UI 
            if (loginResult.success) { 
                // 导航到主屏幕
            } else { 
                // 显示错误消息
            } 
        }) 

        // 为登录按钮设置点击监听器
        loginButton.setOnClickListener { 
            val username = usernameEditText .text.toString() 
            val password = passwordEditText.text.toString() 
            viewModel.login(username, password) 
        } 
    } 
} 

// LoginViewModel.kt (ViewModel) 
class  LoginViewModel ( private  val loginUseCase: LoginUseCase) : ViewModel() {
    private  val loginResult = MutableLiveData<LoginResult>() 

    fun  getLoginResult () : LiveData<LoginResult> = loginResult 

    fun  login (username: String , password: String ) { 
        viewModelScope.launch { 
            val result = loginUseCase.login(username, password) 
            loginResult.值 = 结果
        } 
    } 
}

2. Presentation layer: The presentation layer acts as an intermediary between the UI layer and the domain layer. It contains the ViewModel and any presentation-related logic. Here is an example of a simple LoginViewModel:

// LoginViewModel.kt
类 LoginViewModel ( private  val loginUseCase: LoginUseCase) : ViewModel() { 
    private  val loginResult = MutableLiveData<LoginResult>() 

    fun  getLoginResult () : LiveData<LoginResult> = loginResult 

    fun  login (username: String , password: String ) { 
        viewModelScope.launch { 
            val result = loginUseCase.login(username, password) 
            loginResult.value = result 
        } 
    } 
}

3. Domain layer: The domain layer contains the business logic and use cases of the application. It is independent of the Android framework. Here is an example LoginUseCase:

// LoginUseCase.kt 
class  LoginUseCase ( private  val userRepository: UserRepository) { 
    suspend  fun  login (username: String , password: String ) : LoginResult { 
        // 执行业务逻辑和数据操作
        val user = userRepository.getUserByUsername(username) 

        return  if ( user != null && user.password == password) { 
            LoginResult(success = true , user) 
        } else { 
            LoginResult(success = false , error =“无效的用户名或密码” ) 
        } } 
    }

4. Data layer: The data layer handles data retrieval and storage, interacting with local and remote data sources. Here's an example UserRepository that uses a local database:

// UserRepository.kt 
class  UserRepository ( private  val userDao: UserDao) { 
    suspend  fun  getUserByUsername (username: String ) : User? { 
        // 执行数据库查询或网络请求
        return userDao.getUserByUsername(username) 
    } 
}

5. Dependency injection: To achieve loose coupling and dependency inversion, you can use a dependency injection framework such as Dagger or Koin. Here is an example of dependency injection using Dagger:

// AppModule.kt 
@Module 
class  AppModule { 
    @Provides 
    fun  provideUserRepository (userDao: UserDao ) : UserRepository { 
        return UserRepository(userDao) 
    } 

    @Provides 
    fun  provideLoginUseCase (userRepository: UserRepository ) : LoginUseCase { 
        return LoginUseCase(userRepository) 
    } 
} 

// AppComponent .kt 
@Component(modules = [AppModule::class]) 
interface  AppComponent { 
    fun  inject (loginActivity: LoginActivity )
}

6. Application class: In the Application class, the dependency injection framework needs to be initialized to provide the necessary dependencies. Here is an example:

class  MyApp : Application () { 
    lateinit  var appComponent: AppComponent 

    override  fun  onCreate () { 
        super .onCreate() 
        appComponent = DaggerAppComponent.builder() 
            .appModule(AppModule()) 
            .build() 
    } 
}

Make sure to update the AndroidManifest.xml file to use your custom application class:

<application 
    android:name=".MyApp"“.MyApp”
     ... 
</application>

7. Putting it all together: In order to connect the layers and complete the architecture, you need to make connections between the presentation layer, domain layer, and data layer. Here is an example:

// LoginActivity.kt
类 LoginActivity : AppCompatActivity () { 
    @Inject 
    lateinit  var loginViewModelFactory: LoginViewModelFactory 

    private  lateinit  var viewModel: LoginViewModel 

    override  fun  onCreate (savedInstanceState: Bundle ?) { 
        super .onCreate(savedInstanceState) 
        setContentView(R.layout.activity_login) 

        (应用程序作为MyApp).appComponent.inject( this ) 

        viewModel = ViewModelProvider( this , loginViewModelFactory)
            . get (LoginViewModel:: class .java) 

        // ... 其余代码保持不变
    } 
} 

// LoginViewModelFactory.kt 
class  LoginViewModelFactory ( private  val loginUseCase: LoginUseCase) : 
    ViewModelProvider.Factory { 
    override  fun  <T : ViewModel?> 创建(modelClass: Class < T >) : T { 
        if (modelClass.isAssignableFrom(LoginViewModel:: class .java)) { 
            return LoginViewModel(loginUseCase) as T 
        } 
        throwIllegalArgumentException（“未知的 ViewModel 类”）
    } 
}

Make sure to create the necessary database, DAO and networking related classes according to your specific requirements.

8. Conclusion: By following the principles of MVVM with Clean Architecture, you can create well-organized, maintainable and testable Android applications. The separation of concerns and clear division of layers makes development, debugging, and extensibility easier.

Conclusion: MVVM with its clean architecture provides a solid foundation for building robust and maintainable Android applications. By combining these patterns, you can achieve separation of concerns, testability, and scalability. With a clear understanding of concepts and practical examples, you are now equipped to create high-quality Android applications.

at last

If you want to become an architect or want to break through the 20-30K salary range, then don't be limited to coding and business, but you must be able to select models, expand, and improve programming thinking. In addition, a good career plan is also very important, and the habit of learning is very important, but the most important thing is to be able to persevere. Any plan that cannot be implemented consistently is empty talk.

If you have no direction, here I would like to share with you a set of "Advanced Notes on the Eight Major Modules of Android" written by the senior architect of Ali, to help you organize the messy, scattered and fragmented knowledge systematically, so that you can systematically and efficiently Master the various knowledge points of Android development.

Compared with the fragmented content we usually read, the knowledge points of this note are more systematic, easier to understand and remember, and are arranged strictly according to the knowledge system.

Full set of video materials:

1. Interview collection

2. Source code analysis collection

3. The collection of open source frameworks

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