Dependency injection with Hilt

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Goal

Replace manual dependency wiring with Hilt. Annotate the Application, inject ViewModels with @HiltViewModel, and provide Room and the repository via Hilt modules.

Prerequisites

• Add Room

Gradle setup

// project-level build.gradle.kts
plugins {
    id("com.google.dagger.hilt.android") version "2.53.1" apply false
}

// app-level build.gradle.kts
plugins {
    id("com.google.dagger.hilt.android")
    id("kotlin-kapt")
}

dependencies {
    implementation("com.google.dagger:hilt-android:2.53.1")
    kapt("com.google.dagger:hilt-android-compiler:2.53.1")
    implementation("androidx.hilt:hilt-navigation-compose:1.2.0")
}

Application class

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

@HiltAndroidApp
class App : Application()

Register in AndroidManifest.xml:

<application
    android:name=".App"
    ...>

Hilt module

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 provideDatabase(app: Application): AppDatabase =
        AppDatabase.getInstance(app)

    @Provides
    fun provideItemDao(db: AppDatabase): ItemDao = db.itemDao()

    @Provides @Singleton
    fun provideRepository(dao: ItemDao): ItemRepository =
        ItemRepository(dao, ApiService())
}

Inject ViewModel

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

@HiltViewModel
class ItemViewModel @Inject constructor(
    private val repository: ItemRepository
) : ViewModel() {

    val items: StateFlow<List<ItemEntity>> =
        repository.observeItems()
            .stateIn(viewModelScope, SharingStarted.WhileSubscribed(5000), emptyList())

    fun refresh() = viewModelScope.launch {
        repository.refresh()
    }

    fun toggleFavorite(id: Int) = viewModelScope.launch {
        repository.toggleFavorite(id)
    }
}

In Compose

@Composable
fun ItemScreen(
    viewModel: ItemViewModel = hiltViewModel()
) {
    val items by viewModel.items.collectAsStateWithLifecycle()
    // ...
}

Checkpoint

./gradlew app:build
# BUILD SUCCESSFUL — Hilt generates DI code
# App runs without crash, Room + ViewModel wired through Hilt

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