Error initializing ViewModel (Runtime error)

There is something wrong with the viewModel, somewhere... Everytime i run the app it crashes almost instantly.

The idea of this app is to use clean architecture, consume an API and show it in a recyclerView. For this i use:

Retrofit
Room Database
Dao
Repository
MVVM Architecture

However, i am fairly new to programming and MVVM, and i'm self taught, so I apologise if the error is too obvious, i've been at for some time already, and i need to fix this in order to move forward! So Thank you all for your time in advance...

Here's the code: Main Activity:

class MainActivity : AppCompatActivity() {

    private lateinit var binding: ActivityMainBinding
    private val model: HarryPotterViewModel by viewModels()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = ActivityMainBinding.inflate(layoutInflater)
        setContentView(binding.root)

        CoroutineScope(Dispatchers.IO).launch {

            val charactersList =  model.fetchCharactersApiData()

            initRecyclerView(charactersList)

            Toast.makeText(this@MainActivity, "Characters stored?", Toast.LENGTH_SHORT).show()
        }
    }

    fun initRecyclerView(charactersList: List<Characters>) {
        binding.charactersRecyclerView.layoutManager = GridLayoutManager(this, 3)
        binding.charactersRecyclerView.adapter = CharactersAdapter(charactersList)
    }
}

View Model:

class HarryPotterViewModel(application: Application) : AndroidViewModel(application) {

//    val hpDao by lazy { HarryPotterDatabase(getApplication()).hpDao() }
    private val db by lazy { HarryPotterDatabase.buildDatabase(application) }
    private val repository: HarryPotterRepository = HarryPotterRepository(db)

    val characterList: MutableLiveData<List<Characters>> by lazy {
        MutableLiveData<List<Characters>>()
    }
    val getCharactersData = repository.getCharactersData

    suspend fun fetchCharactersApiData(): List<Characters> {

        // Store characters list from the Api call inside a val
        val apiCharacters = repository.fetchData()

        // Store the list inside the database we created for the app
        insertCharactersData(apiCharacters)

        return apiCharacters
    }

    fun insertCharactersData(characters: List<Characters>) {
        viewModelScope.launch(Dispatchers.IO) {
            repository.insertCharacters(characters)
        }
    }
}

Just in case, i'll also put the code for the Database, DAO & repository, in case i left something important too.

@Database(entities = [Characters::class], version = 1, exportSchema = false)
abstract class HarryPotterDatabase: RoomDatabase() {

    abstract fun hpDao(): HarryPotterDao

    companion object {

        @Volatile
        private var INSTANCE: HarryPotterDatabase? = null

        private val lock = Any()

        operator fun invoke(context: Context) = INSTANCE ?: synchronized(lock) {
                INSTANCE ?: buildDatabase(context).also {
                    INSTANCE = it
                }
            }

        fun buildDatabase(context: Context) = Room.databaseBuilder(
            context.applicationContext,
            HarryPotterDatabase::class.java,
            "harry_potter_database"
        ).build()
    }
}

DAO

@Dao
interface HarryPotterDao {

    @Query("SELECT * FROM characters_table ORDER BY name ASC")
    fun getAllCharactersAtoZ(): LiveData<List<Characters>>

    @Insert(onConflict = OnConflictStrategy.IGNORE)
    fun insertCharactersToDB(characters: List<Characters>)
}

Repository

class HarryPotterRepository(private val db: HarryPotterDatabase) {

    val getCharactersData: LiveData<List<Characters>> = db.hpDao().getAllCharactersAtoZ()
    private val apiCall: Networking = Networking()

    suspend fun fetchData(): List<Characters> {
        return apiCall.retrieveCharacters()
    }

    suspend fun insertCharacters(characters: List<Characters>) {
        db.hpDao().insertCharactersToDB(characters)
    }
}

And of course, the error Logcat:

2021-11-03 01:26:54.139 1403-1619/com.example.myapplication E/AndroidRuntime: FATAL EXCEPTION: DefaultDispatcher-worker-2
    Process: com.example.myapplication, PID: 1403
    java.lang.RuntimeException: Cannot create an instance of class com.example.harryPotterApp.viewmodels.HarryPotterViewModel
        at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.kt:236)
        at androidx.lifecycle.SavedStateViewModelFactory.create(SavedStateViewModelFactory.java:113)
        at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.kt:169)
        at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.kt:139)
        at com.example.harryPotterApp.view.activities.MainActivity$model$2.invoke(MainActivity.kt:22)
        at com.example.harryPotterApp.view.activities.MainActivity$model$2.invoke(MainActivity.kt:21)
        at kotlin.SynchronizedLazyImpl.getValue(LazyJVM.kt:74)
        at com.example.harryPotterApp.view.activities.MainActivity.getModel(MainActivity.kt:21)
        at com.example.harryPotterApp.view.activities.MainActivity.access$getModel(MainActivity.kt:19)
        at com.example.harryPotterApp.view.activities.MainActivity$onCreate$1.invokeSuspend(MainActivity.kt:36)
        at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
        at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:106)
        at kotlinx.coroutines.scheduling.CoroutineScheduler.runSafely(CoroutineScheduler.kt:571)
        at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.executeTask(CoroutineScheduler.kt:750)
        at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.runWorker(CoroutineScheduler.kt:678)
        at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.run(CoroutineScheduler.kt:665)
     Caused by: java.lang.reflect.InvocationTargetException
        at java.lang.reflect.Constructor.newInstance0(Native Method)
        at java.lang.reflect.Constructor.newInstance(Constructor.java:343)
        at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.kt:228)
        at androidx.lifecycle.SavedStateViewModelFactory.create(SavedStateViewModelFactory.java:113) 
        at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.kt:169) 
        at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.kt:139) 
        at com.example.harryPotterApp.view.activities.MainActivity$model$2.invoke(MainActivity.kt:22) 
        at com.example.harryPotterApp.view.activities.MainActivity$model$2.invoke(MainActivity.kt:21) 
        at kotlin.SynchronizedLazyImpl.getValue(LazyJVM.kt:74) 
        at com.example.harryPotterApp.view.activities.MainActivity.getModel(MainActivity.kt:21) 
        at com.example.harryPotterApp.view.activities.MainActivity.access$getModel(MainActivity.kt:19) 
        at com.example.harryPotterApp.view.activities.MainActivity$onCreate$1.invokeSuspend(MainActivity.kt:36) 
        at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33) 
        at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:106) 
        at kotlinx.coroutines.scheduling.CoroutineScheduler.runSafely(CoroutineScheduler.kt:571) 
        at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.executeTask(CoroutineScheduler.kt:750) 
        at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.runWorker(CoroutineScheduler.kt:678) 
        at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.run(CoroutineScheduler.kt:665) 
     Caused by: java.lang.RuntimeException: cannot find implementation for com.example.harryPotterApp.repository.roomdb.database.HarryPotterDatabase. HarryPotterDatabase_Impl does not exist
        at androidx.room.Room.getGeneratedImplementation(Room.java:97)
        at androidx.room.RoomDatabase$Builder.build(RoomDatabase.java:1358)
        at com.example.harryPotterApp.repository.roomdb.database.HarryPotterDatabase$Companion.buildDatabase(HarryPotterDatabase.kt:32)
        at com.example.harryPotterApp.viewmodels.HarryPotterViewModel$db$2.invoke(HarryPotterViewModel.kt:17)
        at com.example.harryPotterApp.viewmodels.HarryPotterViewModel$db$2.invoke(HarryPotterViewModel.kt:17)
        at kotlin.SynchronizedLazyImpl.getValue(LazyJVM.kt:74)
        at com.example.harryPotterApp.viewmodels.HarryPotterViewModel.getDb(HarryPotterViewModel.kt:17)
        at com.example.harryPotterApp.viewmodels.HarryPotterViewModel.<init>(HarryPotterViewModel.kt:19)
        at java.lang.reflect.Constructor.newInstance0(Native Method) 
        at java.lang.reflect.Constructor.newInstance(Constructor.java:343) 
        at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.kt:228) 
        at androidx.lifecycle.SavedStateViewModelFactory.create(SavedStateViewModelFactory.java:113) 
        at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.kt:169) 
        at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.kt:139) 
        at com.example.harryPotterApp.view.activities.MainActivity$model$2.invoke(MainActivity.kt:22) 
        at com.example.harryPotterApp.view.activities.MainActivity$model$2.invoke(MainActivity.kt:21) 
        at kotlin.SynchronizedLazyImpl.getValue(LazyJVM.kt:74) 
        at com.example.harryPotterApp.view.activities.MainActivity.getModel(MainActivity.kt:21) 
        at com.example.harryPotterApp.view.activities.MainActivity.access$getModel(MainActivity.kt:19) 
        at com.example.harryPotterApp.view.activities.MainActivity$onCreate$1.invokeSuspend(MainActivity.kt:36) 
        at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33) 
        at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:106) 
        at kotlinx.coroutines.scheduling.CoroutineScheduler.runSafely(CoroutineScheduler.kt:571) 
        at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.executeTask(CoroutineScheduler.kt:750) 
        at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.runWorker(CoroutineScheduler.kt:678) 
        at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.run(CoroutineScheduler.kt:665)

CodePudding user response：

Do you add the following code in your build.gradle file？

 // To use Kotlin annotation processing tool (kapt)
    kapt("androidx.room:room-compiler:$roomVersion")

It seems like the HarryPotterDatabase_Impl is not generated by kapt yet

CodePudding user response：

Instantiating ViewModel using Delegate property (by viewModels()) cannot be done for ViewModel with argument, you need to implement ViewModelProvider.Factory for creating HarryPotterViewModel since HarryPotterViewModel have argument (application).