Getting started with Dagger2

Dagger 2, a dependency injection framework for Android, simplifies dependency management, resulting in testable, maintainable code. The article outlines Dagger 2 implementation, including component and module creation, dependency scopes, and testing

Getting Started with Dagger 2

Dagger 2 is a widely popular dependency injection framework for Android development. It allows developers to manage dependencies and create lightweight, testable, and maintainable code.

How to Use Dagger 2 for Dependency Injection in Android Apps

To use Dagger 2 in your Android app, you need to follow these steps:

1. Add the Dagger 2 library to your project's build.gradle file:

   <code>dependencies {
    implementation 'com.google.dagger:dagger:2.38.1'
    annotationProcessor 'com.google.dagger:dagger-compiler:2.38.1'
   }</code>

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2. Create a component interface:

   <code>@Component
   interface AppComponent {
    fun inject(activity: MainActivity)  // Members to inject
   }</code>

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3. Create a module to provide the dependencies:

   <code>@Module
   class AppModule {
   
    @Provides
    fun provideRepository(): Repository {
        return RepositoryImpl()  // Assuming RepositoryImpl implements Repository
    }
   }</code>

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4. Initialize the component in your application class:

   <code>class MyApplication : Application() {
    private val appComponent: AppComponent by lazy {
        DaggerAppComponent.builder().appModule(AppModule()).build()
    }
   
    override fun onCreate() {
        super.onCreate()
        appComponent.inject(this)  // Inject the application instance into the component
    }
   }</code>

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Different Dependency Injection Scopes in Dagger 2

Dagger 2 offers different scopes to control the lifetime of injected dependencies:

• @Singleton: Maintains a single instance throughout the application's lifetime.
• @Activity: Provides an instance specific to the current activity.
• @Fragment: Provides an instance specific to the current fragment.
• @ContentView: Provides an instance specific to the current view.

Testing Dependency Hierarchy in Dagger 2

To test your dependency hierarchy, you can use the following approaches:

• Mock Objects: Create mock objects for dependencies that you don't want to instantiate or that have complex dependencies themselves.
• Test Components: Establish a dedicated test component for each test case, allowing you to override specific dependencies for testing.
• Dagger Mock: Use the Dagger Mock library to generate a mock injector, which can be used to inject mock objects into your test.

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