part-3.md

Hilt (Part 3) - Passing different instances of the same type

Part 2

Using @Named annotation

• Inside the @Module class, mark different methods with @Named(SOME_STRING_ID).
• At site of injection as well, use @Named(SOME_STRING_ID). The SOME_STRING_ID passed in the bracket will be used to differentiate which injection goes where.

Full sample code

// ========================================================================
                                                        // Main dependency
                                                        // to inject
class RandomNumberClass
@Inject
constructor(val base: Int)
{
    val value = (Math.random()*100).toInt() * base
}

// ========================================================================
                                                        // Module defining
                                                        // @Named parameters
@InstallIn(ActivityComponent::class)
@Module
class DIModule(){

    @Named("n1")
    @Provides
    fun getRandomNumber1(): RandomNumberClass{
        return RandomNumberClass(3)
    }

    @Named("n2")
    @Provides
    fun getRandomNumber2(): RandomNumberClass{
        return RandomNumberClass(5)
    }

}

// ========================================================================
                                                        // Class needing dependency as
                                                        // CONSTRUCTOR INJECTION
class TestClassAdd
@Inject
constructor(
    @Named("n1") private val n1: RandomNumberClass,       // Corresponds to RandomNumberClass(3)
    @Named("n2") private val n2: RandomNumberClass        // Corresponds to RandomNumberClass(5)
) {
    fun getStringAddition() =
        "Number 1: ${n1.value}, base: ${n1.base}, " +
                "Number 2: ${n2.value}, base: ${n2.base}; Addition: ${n1.value + n2.value}"
}

Using annotation classes

• Declare different annotation class-es
• Instead of using @Named, just use the class name as annotation.

Sample code

// ========================================================================
                                                      // Annotation classes
                                                      // used as "markers"
@Qualifier annotation class n1
@Qualifier annotation class n2           // The @Qualifier part may be optional

// ========================================================================
                                                      // Module using above 
                                                      // annotation classes
                                                      // to differentiate
                                                      // instances of dependencies
@InstallIn(ActivityComponent::class)
@Module
class DIModule(){

    @n1
    @Provides
    fun getRandomNumber1(): RandomNumberClass{
        return RandomNumberClass(3)
    }

    @n2
    @Provides
    fun getRandomNumber2(): RandomNumberClass{
        return RandomNumberClass(5)
    }
}

// ========================================================================
                                                      // Class needing dependencies as
                                                      // CONSTRUCTOR INJECTION
class TestClassAdd
@Inject
constructor(
    @n1 private val n1: RandomNumberClass,       // Corresponds to RandomNumberClass(3)
    @n2 private val n2: RandomNumberClass        // Corresponds to RandomNumberClass(5)
) {
    fun getStringAddition() =
        "Number 1: ${n1.value}, base: ${n1.base}, " +
                "Number 2: ${n2.value}, base: ${n2.base}; Addition: ${n1.value + n2.value}"
}

Part 4