Android Dependency Injection With Hilt Complete Guide

Top 10 Questions and Answers: Android Dependency Injection with Hilt

1. What is Hilt, and why do I need it for Android development?

2. What are the main advantages of using Hilt over vanilla Dagger?

Answer: Hilt provides a simpler setup by reducing the need to write Dagger's boilerplate code like @Component, @Module, and @Provides. It automatically generates the necessary boilerplate and integrates seamlessly with Android’s lifecycle. Hilt comes with pre-built bindings for Android classes like Activity, Fragment, ViewModel, and Application, which are ready for injection, saving you time and reducing the surface area for errors.

3. How do I integrate Hilt into an existing Android project?

Answer: To integrate Hilt into an existing Android project, follow these steps:

1. Add Hilt dependencies: Include the Hilt Gradle plugin and the necessary libraries in your project’s build.gradle files.

// In your project-level build.gradle file
buildscript {
    ext.hilt_version = '2.41'
    dependencies {
        // Other dependencies
        classpath "com.google.dagger:hilt-android-gradle-plugin:$hilt_version"
    }
}

// In your app-level build.gradle file
apply plugin: 'kotlin-kapt'
apply plugin: 'dagger.hilt.android.plugin'

dependencies {
    // Other dependencies
    implementation "com.google.dagger:hilt-android:$hilt_version"
    kapt "com.google.dagger:hilt-compiler:$hilt_version"
}

2. Annotate your Application class: Use @HiltAndroidApp to enable Hilt in the application.

@HiltAndroidApp
class MyApplication : Application()

3. Inject dependencies: Use @Inject to inject dependencies in your Android components.

4. Can Hilt be used with Java?

Answer: Yes, Hilt can be used with Java, but since Hilt was primarily developed with Kotlin in mind, some of its features might not be as seamless. Java developers can still leverage Hilt by using annotations like @Inject, @Module, @InstallIn, and @Provides.

5. What is @InstallIn, and which components can I use it with?

Answer: @InstallIn is a Hilt annotation that tells Hilt which component should be available for dependency injection. Commonly used annotations are:

• SingletonComponent: Dependencies are scoped to the application lifecycle.
• ActivityComponent: Dependencies are scoped to the lifecycle of an Android Activity.
• ActivityRetainedComponent: Dependencies are scoped to the retained state of an Activity.
• FragmentComponent: Dependencies are scoped to the lifecycle of an Android Fragment.
• ViewModelComponent: Dependencies are scoped to a ViewModel instance.
• ViewComponent: Dependencies are scoped to the lifecycle of a View.
• ViewWithFragmentComponent: Dependencies are scoped to the lifecycle of a View that is associated with a Fragment.
• ApplicationContextComponent and ActivityContextComponent: Useful for injecting the application and activity contexts.

6. How do you inject ViewModel using Hilt?

Answer: You can inject ViewModel using HiltViewModelFactory and ViewModelProvider. Here’s an example:

@HiltViewModel
class MyViewModel @Inject constructor(private val repo: Repository) : ViewModel() {
    // Implementation
}

class MyActivity : AppCompatActivity() {

    private val viewModel: MyViewModel by viewModels()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        // Use viewModel
    }
}

7. What is a @Module in Hilt, and when should you use it?

Answer: A @Module in Hilt is used to provide dependencies that can’t be easily injected automatically, like third-party libraries or platform services. You define the module with @Module and @InstallIn annotations, and use @Provides methods to specify how these dependencies should be created.

Example:

@Module
@InstallIn(SingletonComponent::class)
object NetworkModule {
    @Provides
    fun provideRetrofit(): Retrofit {
        return Retrofit.Builder()
            .baseUrl(BASE_URL)
            .addConverterFactory(GsonConverterFactory.create())
            .build()
    }

    @Provides
    fun provideApiService(retrofit: Retrofit): ApiService {
        return retrofit.create(ApiService::class.java)
    }
}

8. How can I provide multiple implementations of the same interface in Hilt?

Answer: You can provide multiple implementations of the same interface using @Qualifier. Define a custom annotation and use it to distinguish between implementations.

Example:

@Qualifier
@Retention(AnnotationRetention.BINARY)
annotation class RemoteDataSource

@Qualifier
@Retention(AnnotationRetention.BINARY)
annotation class LocalDataSource

@Module
@InstallIn(SingletonComponent::class)
object DataSourceModule {
    @Provides
    @RemoteDataSource
    fun provideRemoteDataSource(): DataSource {
        return RemoteDataSourceImpl()
    }

    @Provides
    @LocalDataSource
    fun provideLocalDataSource(): DataSource {
        return LocalDataSourceImpl()
    }
}

class Repository @Inject constructor(
    @RemoteDataSource private val remoteDataSource: DataSource,
    @LocalDataSource private val localDataSource: DataSource
)

9. What are some best practices to follow when using Hilt?

Answer: Some best practices for using Hilt include:

• Use @InstallIn wisely: Only use @InstallIn when necessary and scope your dependencies appropriately.
• Avoid overusing @Provides: Only use @Provides for non-standard cases. Inject directly wherever possible.
• Use qualifiers for disambiguation: If you provide multiple implementations of the same type, use @Qualifier to distinguish between them.
• Test your code: Write unit tests for your ViewModel and other components to ensure they have the correct dependencies.

10. How do I debug issues related to Hilt?

Answer: Debugging issues in Hilt can be achieved using the following strategies:

• Check logcat: Hilt provides detailed error messages in logcat, helping you pinpoint dependency resolution issues.
• Use Android Studio's navigation: Navigate between dependencies and their providers using the IDE’s built-in features.
• Verify your dependencies: Double-check that all your dependencies are properly annotated and scoped.
• Test with @EntryPoint: Use @EntryPoint to create a custom entry point for testing purposes and verify if dependencies are correctly injected.