Mastering Hilt - Android | Kotlin | Hilt (Dagger 2) [Part 3]

Providing Dependencies with Hilt

• Singleton Binding

• Provides Annotation

• Binds Annotation

Singleton Binding:

The @Singleton annotation is used in Hilt to mark a class as a singleton, ensuring that only one instance of that class is created and shared across the entire application.

Example:

@Singleton
class MySingletonClass @Inject constructor() {
    init {
        // Initialization code
    }
}

In this example, the MySingletonClass is marked with @Singleton, making it a singleton class. Hilt will ensure that there is only one instance of MySingletonClass throughout the application's lifecycle. Anytime this class is injected into other classes, they will receive the same instance.

Provides Annotation:

The @Provides annotation is used in Hilt to define how to create and provide instances of specific classes or interfaces. This is typically used within a Hilt module.

Example:

@Module
@InstallIn(SingletonComponent::class)
object MyModule {
    @Singleton
    @Provides
    fun provideMyDependency(): MyDependency {
        return MyDependencyImpl()
        }
}

In this example, MyModule is a Hilt module that provides a dependency called MyDependency. The @Provides annotation indicates that this function will provide an instance of MyDependency. When any class requests an instance of MyDependency, Hilt will use this function to create and provide it.

Binds Annotation:

The @Binds annotation is used in Hilt to tell the framework how to provide an implementation for an interface or an abstract class. This is typically used within a Hilt module.

Example:

@Module
@InstallIn(SingletonComponent::class)
abstract class MyModule {
    @Singleton
    @Binds
    abstract fun bindMyDependency(impl: MyDependencyImpl): MyDependency
}

In this example, MyModule is a Hilt module that provides a binding for the MyDependency interface. The @Binds annotation tells Hilt that when an instance of MyDependency is requested, it should use MyDependencyImpl as the concrete implementation.

These are the three common methods to provide dependencies with Hilt. We can choose the appropriate method based on the scenario and your project's needs. Hilt will automatically handle the dependency injection for us based on these annotations and configurations.