Dependency injection with Hilt in depth in Android Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to annotate an Android Application class for Hilt.

Android Kotlin

import android.app.Application
import dagger.hilt.android.HiltAndroidApp

@[1]
class MyApp : Application() {}

Drag options to blanks, or click blank then click option'

AHiltAndroidApp

BInject

CModule

DProvides

Attempts:

3 left

💡 Hint

Common Mistakes

Using @Inject instead of @HiltAndroidApp

Forgetting to annotate the Application class

Using @Module or @Provides on the Application class

The @HiltAndroidApp annotation tells Hilt to generate components for the Application class.

2fill in blank

medium

Complete the code to inject a dependency into an Android Activity using Hilt.

Android Kotlin

import android.os.Bundle
import androidx.activity.ComponentActivity
import dagger.hilt.android.AndroidEntryPoint
import javax.inject.Inject

@AndroidEntryPoint
class MainActivity : ComponentActivity() {
    @Inject lateinit var repository: [1]

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
    }
}

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AModule

BInject

CMyRepository

DProvides

Attempts:

3 left

💡 Hint

Common Mistakes

Using @Inject as the type instead of the class name

Not annotating the Activity with @AndroidEntryPoint

Forgetting to declare the variable as lateinit

The dependency type to inject must be specified. Here, MyRepository is the class to be injected.

3fill in blank

hard

Fix the error in the Hilt module by completing the annotation to provide a singleton instance.

Android Kotlin

import dagger.Module
import dagger.Provides
import dagger.hilt.InstallIn
import dagger.hilt.components.SingletonComponent
import javax.inject.Singleton

@Module
@InstallIn(SingletonComponent::class)
object AppModule {
    @[1]
    fun provideService(): ApiService {
        return ApiServiceImpl()
    }
}

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ASingleton

BInject

CHiltAndroidApp

DAndroidEntryPoint

Attempts:

3 left

💡 Hint

Common Mistakes

Using @Inject instead of @Singleton on provider methods

Forgetting to annotate the module with @InstallIn

Using @AndroidEntryPoint or @HiltAndroidApp on provider methods

The @Singleton annotation ensures the provided instance is a singleton in the app scope.

4fill in blank

hard

Fill both blanks to create a Hilt module that provides a Retrofit instance.

Android Kotlin

import dagger.Module
import dagger.Provides
import dagger.hilt.InstallIn
import dagger.hilt.components.SingletonComponent
import retrofit2.Retrofit
import retrofit2.converter.gson.GsonConverterFactory
import javax.inject.Singleton

@Module
@InstallIn(SingletonComponent::class)
object NetworkModule {
    @Singleton
    @Provides
    fun provideRetrofit(): Retrofit {
        return Retrofit.Builder()
            .baseUrl([1])
            .addConverterFactory([2])
            .build()
    }
}

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A"https://api.example.com/"

BGsonConverterFactory.create()

CRetrofit.create()

D"http://localhost/"

Attempts:

3 left

💡 Hint

Common Mistakes

Using Retrofit.create() instead of GsonConverterFactory.create()

Forgetting quotes around the base URL string

Using a wrong URL like localhost for production

The base URL must be a string with the API endpoint. The converter factory is created by calling GsonConverterFactory.create().

5fill in blank

hard

Fill all three blanks to create a Hilt ViewModel with an injected repository and a saved state handle.

Android Kotlin

import androidx.lifecycle.SavedStateHandle
import androidx.lifecycle.ViewModel
import dagger.hilt.android.lifecycle.HiltViewModel
import javax.inject.Inject

@HiltViewModel
class UserViewModel @Inject constructor(
    private val repository: [1],
    private val savedStateHandle: [2]
) : ViewModel() {

    fun getUserId(): String? {
        return savedStateHandle.get<String>([3])
    }
}

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AUserRepository

BSavedStateHandle

C"userId"

DViewModel

Attempts:

3 left

💡 Hint

Common Mistakes

Using ViewModel as a type for savedStateHandle

Forgetting quotes around the key string

Using wrong repository class name

The repository type is UserRepository. The saved state handle type is SavedStateHandle. The key to get the user ID is the string "userId".