Dependency injection with Hilt-4 (Annotation)

Outline :

Annotation used for sorting when using an interface in more than one class. Determines which action we will do first.

A qualifier is an annotation that you use to identify a specific binding for a type when that type has multiple bindings defined.

Scope :

Create a second Implementer class

class SecondInterfaceImplementor
@Inject constructor() : MyInterface
{
    override fun myPrintFunction(): String {
        return "My Second Interface Implementor"
    }
}

Adding Annotation’s values which are Qualifier and Retention

interface MyInterface {
    fun myPrintFunction() : String
}

@InstallIn(SingletonComponent::class)
@Module
class MyModule{
    @FirstImplementor
    @Singleton
    @Provides
    fun providerFunction():MyInterface{
        return InterfaceImplementor()
    }
    @SecondImplementor
    @Singleton
    @Provides
    fun secondProviderFunction():MyInterface {
        return SecondInterfaceImplementor()
    }

    @Singleton
    @Provides
    fun gSonProvider() : Gson{
        return Gson()
    }
}
//These are explain that you would use annotation
@Qualifier
@Retention(AnnotationRetention.BINARY)
annotation class FirstImplementor

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

Edit ClassExample class and show them in MainActivity

class ClassExample
@Inject constructor(@FirstImplementor private val myInterfaceImplementor: MyInterface,
                    private val gson : Gson,
                    @SecondImplementor private val mySecondInterfaceImplementor: MyInterface) {
    fun myFunction() : String {
        return "Working: ${myInterfaceImplementor.myPrintFunction()}"
    }
    fun mySecondFunction() : String {
        return "Working: ${mySecondInterfaceImplementor.myPrintFunction()}"
    }
}

Result :

println(myClass.myFunction())
println(myClass.mySecondFunction())
//Logcat
System.out: My interface Implementor
System.out: My Second Interface Implementor

I would like to thank Atıl Samancıoglu and Google who helped me understand this topic.

Atıl Samancıoglu : https://atilsamancioglu.com/

https://developer.android.com/training/dependency-injection/hilt-android#hilt-modules