getting wrong data from RoomDB. GetCount() using CoroutineScope is not working-CodePudding

I have a login app which uses Navigation Activity, JetPack and RoomDB. It has LoginFragment, LoginVieweModel, LoginDatabase, LoginDao and login Repository. I don't know the correct syntax to get UserCount from RoomDB.

The whole app is located in GitHub at https://github.com/msyusuf/LoginFragNavActivity.git.

Code in LoginDao is

@Query("SELECT COUNT(*) FROM loggedin_user_table")
suspend fun getLoggedInUserCount(): Int

Code in LoginViewModel is

fun getUserCount(): Int {
    var count: Int = 99
    viewModelScope.launch {
        count = loginRepository.getUserCount()
        Log.i(LOG_TAG, "In LoginViewModel.getUserCount(): count = $count")
    }
    return count
}

The fun getUserCount() does not have count from repository, it 99 which I used to initialize the count variable.

CodePudding user response：

In getUserCount() function of LoginViewModel class a coroutine, launched using launch builder, will be executed after the function returns. You should think about how you want to use the data. If you want it to be used just as an input data for some another calculations then it make sense to make the getUserCount() function suspend:

suspend fun getUserCount(): Int {
    val count: Int = loginRepository.getUserCount()
    Log.i(LOG_TAG, "In LoginViewModel.getUserCount(): count = $count")
    return count
}

If you want it to be displayed in UI you can make it suspend like above and call it in a coroutine using lifecycleScope:

in Activity/Fragment

lifecycleScope.launch {
    val count = viewModel.getUserCount()
    // update UI
}

Another alternative is to apply reactive approach using LiveData or Kotlin Flow

CodePudding user response：

You can return values from coroutine scope using withContext here read the documentation -> https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines/with-context.html

you can change the function like this

suspend fun getUserCount(): Int {
    return withContext(Dispatchers.IO) {
        val count = loginRepository.getUserCount()
        Log.i(LOG_TAG, "In LoginViewModel.getUserCount(): count = $count")
        count
    }
}