Hello developers,

In the course of developing Android applications, integrating various libraries can sometimes lead to unexpected issues. Recently, we encountered a significant problem while using Room for database management and Koin for dependency injection in our Kotlin Android project. Specifically, Koin was unable to inject the DAO at runtime, causing the application to crash. In this blog post, we'll delve into this issue and provide a solution to fix it.

The Issue: Koin Failing to Inject DAO

When using Koin to inject Room's DAO, we encountered a runtime crash. The error indicated that Koin could not find the DAO dependency, despite being properly defined. This problem is typically due to the lifecycle and initialization order of Room and Koin.

Here’s a simplified version of the setup that caused the issue:

// Database definition
@Database(entities = [User::class], version = 1)
abstract class AppDatabase : RoomDatabase() {
abstract fun userDao(): UserDao
}

// Koin module
val appModule = module {
    single {
        Room.databaseBuilder(get(), AppDatabase::class.java, "my_database")
            .build()
    }
    single { get<AppDatabase>().userDao() }
}

// DAO
@Dao
interface UserDao {
    @Query("SELECT * FROM user")
    fun getAllUsers(): List<User>
}

Despite having the DAO defined correctly, the application would crash when trying to inject `UserDao`.

The Fix: Correcting the Koin and Room Integration

To resolve this issue, we need to ensure that the Room database and its DAO are correctly initialized and provided to Koin. Here’s a step-by-step guide to fix the problem:

1. Ensure Proper Initialization Order: Make sure the database is created before attempting to access the DAO.

2. Update Koin Module: Correctly define the database and DAO dependencies in the Koin module.

Here’s the updated code that resolves the issue:

// Correct Koin module
val appModule = module {
    single {
        Room.databaseBuilder(get(), AppDatabase::class.java, "my_database")
            .fallbackToDestructiveMigration()
            .build()
    }

    // Using factory instead of single for DAO
    factory { get<AppDatabase>().userDao() }
}

// Application class
class MyApplication : Application() {
    override fun onCreate() {
        super.onCreate()
        startKoin {
            androidContext(this@MyApplication)
            modules(appModule)
        }
    }
}

// Injecting UserDao in a ViewModel
class UserViewModel(private val userDao: UserDao) : ViewModel() {
    fun getUsers() = userDao.getAllUsers()
}

// Koin module for ViewModel
val viewModelModule = module {
    viewModel { UserViewModel(get()) }
}

Explanation of the Fix

1. Database Initialization: The `Room.databaseBuilder` is used to create the `AppDatabase` instance. By calling `build()` on the `Room.databaseBuilder`, we ensure that the database is fully constructed before any DAO is accessed.

2. DAO Injection with Factory: Using `factory` instead of `single` for the DAO ensures that a new instance of the DAO is provided each time it's injected. This is crucial for DAOs since they are tightly coupled with the database lifecycle.

3. Starting Koin: In the `Application` class, Koin is started with the Android context and the required modules. This ensures that the dependencies are properly set up when the application starts.

4. ViewModel Integration: The `UserViewModel` is defined to receive `UserDao` as a dependency. The Koin module for ViewModel uses `viewModel { UserViewModel(get()) }` to inject the DAO correctly.

Conclusion

Integrating Room and Koin in a Kotlin Android project can sometimes lead to issues if not set up correctly. By ensuring the proper initialization order and using `factory` for DAO injection, we can resolve runtime crashes related to dependency injection. This approach helps maintain a clean and efficient architecture, leveraging the best of Room for database management and Koin for dependency injection.

If you encounter similar issues or have any questions, feel free to reach out or leave a comment below. Happy coding!

Max-Pad on GitHub