How to Use Hilt for Dependency Injection in Android

To use Hilt for dependency injection in Android, add the Hilt dependencies and apply the @HiltAndroidApp annotation to your Application class. Then, annotate Android components with @AndroidEntryPoint and provide dependencies using @Module and @Inject annotations.

Syntax

Hilt uses annotations to manage dependencies easily:

• @HiltAndroidApp: Marks your Application class to trigger Hilt code generation.
• @AndroidEntryPoint: Marks Activities, Fragments, or other Android classes to receive dependencies.
• @Module and @InstallIn: Define how to provide dependencies.
• @Inject: Requests or provides dependencies.

kotlin

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

@HiltAndroidApp
class MyApplication : Application() {
}

import dagger.hilt.android.AndroidEntryPoint
import androidx.appcompat.app.AppCompatActivity
import javax.inject.Inject

@AndroidEntryPoint
class MainActivity : AppCompatActivity() {
    @Inject lateinit var repository: MyRepository
}

Example

This example shows a simple setup where a repository is injected into an Activity using Hilt.

kotlin

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

@HiltAndroidApp
class MyApplication : Application()

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 {
    @Provides
    @Singleton
    fun provideRepository(): MyRepository = MyRepository()
}

class MyRepository {
    fun getData() = "Hello from Repository"
}

import dagger.hilt.android.AndroidEntryPoint
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.TextView
import javax.inject.Inject

@AndroidEntryPoint
class MainActivity : AppCompatActivity() {
    @Inject lateinit var repository: MyRepository

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        val textView = TextView(this)
        textView.text = repository.getData()
        setContentView(textView)
    }
}

Output

The app screen shows a TextView with text: "Hello from Repository"

Common Pitfalls

Common mistakes when using Hilt include:

• Forgetting to annotate the Application class with @HiltAndroidApp, which disables Hilt setup.
• Not annotating Activities or Fragments with @AndroidEntryPoint, so injection fails.
• Trying to inject interfaces or classes without providing a binding in a @Module.
• Using constructor injection in classes not managed by Hilt.

kotlin

/* Wrong: Missing @HiltAndroidApp on Application */
class MyApplication : Application()

/* Right: Add @HiltAndroidApp */
@HiltAndroidApp
class MyApplication : Application()

Quick Reference

Remember these key annotations and their roles:

Annotation	Purpose
@HiltAndroidApp	Setup Hilt in Application class
@AndroidEntryPoint	Enable injection in Android components
@Module	Define how to provide dependencies
@InstallIn	Specify component scope for modules
@Inject	Request or provide dependencies

Key Takeaways

Add @HiltAndroidApp to your Application class to enable Hilt.

Use @AndroidEntryPoint on Activities or Fragments to inject dependencies.

Provide dependencies with @Module and @Provides or constructor @Inject.

Always declare bindings for interfaces or abstract classes in modules.

Check annotations carefully to avoid common injection errors.