Understanding Android Dependency Injection

Android Dependency Injection (DI) is a technique that decouples the components of an application and makes it easy to manage dependencies. With DI, developers can write modular, testable, and maintainable code. In simple terms, DI is the process of providing an object with the dependencies it requires, instead of creating them within the object itself. This way, objects can be easily reused and tested, and it makes the application more flexible and extensible.

There are several DI frameworks available for Android development, but two of the most popular ones are Hilt and Dagger. In this article, we’ll compare Hilt and Dagger and provide a guide to each framework.

Hilt vs Dagger: A Comparison of DI Frameworks

Hilt and Dagger are both DI frameworks for Android that are based on Google’s DI specification. Hilt is a new DI framework that was introduced in 2020, and it is built on top of Dagger. Hilt simplifies the process of DI by providing a set of annotations and a pre-defined set of components that can be used to inject dependencies. Dagger, on the other hand, is a more advanced DI framework that offers a lot of flexibility and customization options.

One of the main differences between Hilt and Dagger is that Hilt generates a lot of boilerplate code automatically, while Dagger requires more manual setup. Hilt also provides a simpler syntax for defining components and modules, which makes it easier to use for beginners. Dagger, on the other hand, offers more advanced features, such as lazy injection, method injection, and subcomponents.

Hilt: A Beginner’s Guide to Android DI

Hilt is a great DI framework for beginners, as it simplifies the process of DI and reduces the amount of boilerplate code that needs to be written. Hilt provides a set of annotations that can be used to inject dependencies into classes, such as @Inject, @Provides, @Singleton, and @ViewModelInject.

To get started with Hilt, you need to add the following dependencies to your project:

implementation 'com.google.dagger:hilt-android:2.37'
kapt 'com.google.dagger:hilt-compiler:2.37'

Once you’ve added the dependencies, you need to annotate your Application class with @HiltAndroidApp to enable Hilt in your app. You can then use the @Inject annotation to inject dependencies into your classes, like this:

class MyViewModel @ViewModelInject constructor(
    private val repository: MyRepository
) : ViewModel() {
    // ...
}

Dagger: Advanced Android DI Techniques and Best Practices

Dagger is a more advanced DI framework that offers a lot of flexibility and customization options. With Dagger, you can define custom scopes, create subcomponents, use lazy injection, and more. However, Dagger requires more manual setup than Hilt and can be more complex to use.

To use Dagger in your project, you need to add the following dependencies:

implementation 'com.google.dagger:dagger:2.x'
kapt 'com.google.dagger:dagger-compiler:2.x'

Once you’ve added the dependencies, you need to define your components and modules. Components define the injection targets, while modules provide the dependencies. You can use the @Component and @Module annotations to define your components and modules, respectively.

@Component(modules = [MyModule::class])
interface MyComponent {
    fun inject(activity: MainActivity)
}

@Module
class MyModule {
    @Provides
    fun provideMyDependency(): MyDependency {
        return MyDependencyImpl()
    }
}

Dagger also provides advanced features, such as subcomponents and lazy injection. Subcomponents allow you to create a component that depends on another component, while lazy injection delays the injection of dependencies until they are actually needed.

In conclusion, Android Dependency Injection is a powerful technique that can greatly improve the maintainability, testability, and flexibility of your Android applications. Hilt and Dagger are both great DI frameworks for Android, and choosing between them depends on your specific needs and experience level. Hilt is a great option for beginners, while Dagger offers more advanced features for experienced developers. Regardless of which framework you choose, implementing DI in your Android application will greatly improve its quality and maintainability.