Method addObserver must be called on the main thread Exception, While inserting data to room database - android-room

Question

I am trying to insert data into the room database using the kotlin coroutine. But I always get an exception java.lang.IllegalStateException: Method addObserver must be called on the main thread
But I don't have an observer in this code, the insert call is called from launch with Dispatchers IO
DocumentDao.kt
#Dao
interface DocumentDao {
#Insert
suspend fun insertDocument(document: Document): Long
}
Repository.kt
class Repository#Inject constructor(val db: MyDB) {
suspend fun demoInsert(
uri: String,
albumId: Long
): Long {
val newDoc = Document(0, albumId, rawUri = uri)
return db.documentDao().insertDocument(newDoc)
}
}
MyViewModel.kt
#HiltViewModel
class MyViewModel#Inject constructor(val repo: Repository) : ViewModel() {
suspend fun demoInsert(
uri: String,
albumId: Long
): Long {
return repo.demoInsert(uri, albumId)
}
}
MyFrag.kt
#AndroidEntryPoint
class MyFrag: Fragment() {
val viewModel: MyViewModel by viewModels()
....
....
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
binding.insert.setOnClickListener {
lifecycleScope.launch(Dispatchers.IO) {
val res = viewModel.demoInsert("test", Random.nextLong(500))
Log.d(TAG, "onViewCreated: $res")
}
}
........
.......
}
}
what is wrong with this code? please help me

Answer 1

I'm not sure about this but you can launch coroutine inside listener with Main Dispatcher and later use withContext inside DB function, to change context.

Answer 2

I was facing the same issue and I solved yhis way :
private fun insertAllItemsInDb(data : List<PostResponse>){
val listPost = data.map { it.toUI() }
val scope = CoroutineScope(Job() + Dispatchers.Main)
scope.launch {
localViewModel.insertAllPosts(listPost)
}
}
ViewModel:
fun insertAllPosts(posts: List<PostItem>) {
viewModelScope.launch {
dbRepository.insertAllPosts(posts)
}
}

Answer 3

Creating view model with:
val viewModel: MyViewModel by viewModels()
Will result in lazy creating. Creation of real object will be performed when you access your object for first time. This happens inside:
lifecycleScope.launch(Dispatchers.IO) {
val res = viewModel.demoInsert("test", Random.nextLong(500))
Log.d(TAG, "onViewCreated: $res")
}
And since implementation of method viewModels<>() looks like this:
#MainThread
public inline fun <reified VM : ViewModel> Fragment.viewModels(
noinline ownerProducer: () -> ViewModelStoreOwner = { this },
noinline factoryProducer: (() -> Factory)? = null
): Lazy<VM> = createViewModelLazy(VM::class, { ownerProducer().viewModelStore }, factoryProducer)
You are getting
Method addObserver must be called on the main thread
You should be able to fix this with something like this.
lifecycleScope.launch(Dispatchers.IO) {
val res = withContext(Dispatchers.Main + lifecycleScope.coroutineContext){}.demoInsert("test", Random.nextLong(500))
Log.d(TAG, "onViewCreated: $res")
}

Answer 4

MyViewModel.kt
#HiltViewModel
class MyViewModel#Inject constructor(val repo: Repository) : ViewModel() {
suspend fun demoInsert(
uri: String,
albumId: Long
): Long {
viewModelScope.launch {
repo.demoInsert(uri, albumId)
}
}
}
MyFrag.kt
#AndroidEntryPoint
class MyFrag: Fragment() {
val viewModel: MyViewModel by viewModels()
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
binding.insert.setOnClickListener {
lifecycleScope.launch(Dispatchers.Main) {
viewModel.demoInsert("test", Random.nextLong(500))
}
}
}
}