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How to properly set Observable in the Activity to Pass data from API call in view model into Activity + Data Class for the list. Android Compose

I think my observable is set incorrectly here. I am using Retrofit2 + Moshi as the deserializer, and the API call from Retrofit is working.
But once I make the API call, I am trying to set up the Observable in my Activity and then use the API call data from the data class.
Here is my view model code:
class DealsViewModel(val repository: MainRepository) : ViewModel() {
val movieList = MutableLiveData<List<DealItems>>()
var job: Job? = null
val loading = MutableLiveData<Boolean>()
val errorMessage = MutableLiveData<String>()
val exceptionHandler = CoroutineExceptionHandler { _, throwable ->
onError("Exception handled: ${throwable.localizedMessage}")
}
fun getMovies() {
viewModelScope.launch{
// View Model Scope gives the Coroutine that will be canceled when the ViewModel is cleared.
job = CoroutineScope(Dispatchers.IO + exceptionHandler).launch {
val items = repository.getProduct()
withContext(Dispatchers.Main) {
if (items.isNullOrEmpty()) {
loading.value = false
// put error message in here later
} else {
dealList.postValue(items)
return#withContext
}
}
}
}
}
private fun onError(message: String) {
errorMessage.value = message
loading.value = false
}
override fun onCleared() {
super.onCleared()
job?.cancel()
}
}
And here is my MainActivity code.
I am using JetpackCompose in my activity, LiveData for the API response container. In my main repository is where I am validating a successful API response and then the coroutines for the call are inside of the view model.
My API call is successful, but I am not sure where to call the ViewModel.GetMovies() inside of the activity and I am not sure if the observables are set properly and/or where to pass the API's livedata into my composable function.
Thanks for any help you can provide. I am new to android and trying to use Coroutines for the first time.
class MainActivity: ComponentActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
val retrofitService = RetrofitService.getInstance()
val viewModel = ViewModelProvider(this,
MyViewModelFactory(MainRepository(retrofitService = retrofitService))).get(DealsViewModel::class.java)
// viewModel.getProducts()
setContent {
myApp {
MyScreenContent()
}
viewModel.movieList.observe(
this, { it ->
if( it != null) {
it.forEach {
var movieLocation = it.movieLocation
val description = it.description
val id = it.id
val title = it.title
val regularPrice = it.regularPrice
}
}
})
return#setContent
}
viewModel.errorMessage.observe(this, {
Toast.makeText(this, it, Toast.LENGTH_SHORT).show()
})
viewModel.loading.observe(
this,
Observer {
if (it) {
}
})
}
}

I assume that it always depends when should you call especially in the activity we have many lifecycles; however, the best way is to use the .also on the livedata/stateflow lazy creation so that you do guarantee as long as the view model is alive, the getMovies is called only one time, and also guarantee the service itself is not called unless someone is listening to it.
You may check the full documentation in this link
Here is a code example
class MyViewModel : ViewModel() {
private val users: MutableLiveData<List<User>> by lazy {
MutableLiveData<List<User>>().also {
loadUsers()
}
}
fun getUsers(): LiveData<List<User>> {
return users
}
private fun loadUsers() {
// Do an asynchronous operation to fetch users.
}
}
When using this code, you do not have to call getMovies at all in the activity, you just listen to the observer.

Android: Why doesn't this Transformation.map run when trying to assign to a variable?

I am trying to use the Firebase API in my project but Transformations.map for the variable authenticationState in the View Model does not run. I have been following Google's tutorial here (link goes to the ViewModel of that project).
I want to be able to add the Transformations.map code to the FirebaseUserLiveData file later but I cant seem to figure out why it doesn't run.
FirebaseUserLiveData
class FirebaseUserLiveData: LiveData<FirebaseUser?>() {
private val firebaseAuth = FirebaseAuth.getInstance()
private val authStateListener = FirebaseAuth.AuthStateListener { firebaseAuth ->
value = firebaseAuth.currentUser
}
override fun onActive() {
firebaseAuth.addAuthStateListener { authStateListener }
}
override fun onInactive() {
firebaseAuth.removeAuthStateListener(authStateListener)
}
}
SearchMovieFragmentViewModel
class SearchMovieFragmentViewModel : ViewModel() {
enum class AuthenticationState {
AUTHENTICATED, UNAUTHENTICATED, INVALID_AUTHENTICATION
}
var authenticationState = Transformations.map(FirebaseUserLiveData()) { user ->
Log.d("TEST", "in the state function")
if (user != null) {
AuthenticationState.AUTHENTICATED
} else {
AuthenticationState.UNAUTHENTICATED
}
}
SearchMovieFragment
class SearchMovieFragment : Fragment(), MovieSearchItemViewModel {
companion object {
fun newInstance() = SearchMovieFragment()
}
private lateinit var searchMovieFragmentViewModel: SearchMovieFragmentViewModel
private lateinit var binding: SearchMovieFragmentBinding
private lateinit var movieRecyclerView: RecyclerView
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
binding = DataBindingUtil.inflate(inflater, R.layout.search_movie_fragment, container, false)
searchMovieFragmentViewModel = ViewModelProvider(this).get(SearchMovieFragmentViewModel::class.java)
binding.lifecycleOwner = this
binding.viewmodel = searchMovieFragmentViewModel
binding.signOutButton.setOnClickListener {
AuthUI.getInstance().signOut(requireContext())
}
searchMovieFragmentViewModel.authenticationState.observe(viewLifecycleOwner, Observer { state ->
when (state) {
AUTHENTICATED -> searchMovieFragmentViewModel.signedIn = View.VISIBLE
UNAUTHENTICATED -> searchMovieFragmentViewModel.signedIn = View.GONE
}
})
return binding.root
}
}

Should be .addAuthStateListener(authStateListener) instead of { authStateListener }

That is because you are not keeping the reference of FirebaseUserLiveData() once you start observing it like Transformations.map(FirebaseUserLiveData()) { user ->.
You have to have the reference of the Livedata you are mapping or transferring to another form of Livedata.
It is like a chain of observation, All LiveData in the chain should be observed or should have some kind of observer down the line, The main use-case is to transform some form of livedata to something you want, For Example:
class YourRepository{ // your repo, that connected to a network that keeps up to date some data
val IntegerResource: LiveData<Int> = SomeRetrofitInstance.fetchFromNetwork() //updating some resource from network
}
class YourViewModel{
val repository = YourRepository()
//this will start observe the repository livedata and map it to string resource
var StringResource: Livedata<String> = Transformations.map( repository.IntegerResource ) { integerValue ->
integerValue.toString()
}
My Point is you have to keep alive the LiveData you are transforming. Hope helped.

Working with multiple repositories in one ViewModel on kotlin

Tell me, please, how to make it more correct so that the ViewModel supports working with the desired repository, depending on the viewmodel's parameter? Android application should display a list of requests, requests are of different types. I want to use one fragment for request of different types and in one model I want universally work with a repository that will pull out requests of the required type from the database (Room).
I made a common interface for repositories:
interface RequestRepository<T> {
fun getRequests(): LiveData<List<T>>
fun getRequestById(requestId: String): LiveData<T>
suspend fun insertRequests(requests: List<T>)
suspend fun deleteRequest(request: T)
suspend fun deleteAllRequests()
}
This is one of the repositories:
class PaymentRequestRepository private constructor(private val paymentRequestDao: PaymentRequestDao) : RequestRepository<PaymentRequest> {
override fun getRequests() = paymentRequestDao.getRequests()
override fun getRequestById(requestId: String) = paymentRequestDao.getRequestById(requestId)
override suspend fun insertRequests(requests: List<PaymentRequest>) {
paymentRequestDao.deleteAll()
paymentRequestDao.insertAll(requests)
}
override suspend fun deleteRequest(request: PaymentRequest) = paymentRequestDao.delete(request)
override suspend fun deleteAllRequests() = paymentRequestDao.deleteAll()
companion object {
// For Singleton instantiation
#Volatile private var instance: PaymentRequestRepository? = null
fun getInstance(paymentRequestDao: PaymentRequestDao) =
instance ?: synchronized(this) {
instance ?: PaymentRequestRepository(paymentRequestDao).also { instance = it }
}
}
}
How in the ViewModel to work with the necessary repository depending on the type of request?
class RequestListViewModel(application: Application, val requestType: RequestType): AndroidViewModel(application) {
//lateinit var paymentRequestRepository: PaymentRequestRepository
//lateinit var serviceRequestRepository: ServiceRequestRepository
lateinit var requestRepository: RequestRepository<BaseRequestDao<Request>>
...
init {
val database = AgreementsDatabase.getDatabase(application)
when (requestType) {
RequestType.MONEY -> {
val paymentRequestDao = database.paymentRequestsDao()
requestRepository = PaymentRequestRepository.getInstance(paymentRequestDao)
}
RequestType.SERVICE -> {
val serviceRequestDao = database.serviceRequestsDao()
requestRepository = ServiceRequestRepository.getInstance(serviceRequestDao)
}
RequestType.DELIVERY -> {
val deliveryRequestsDao = database.deliveryRequestsDao()
requestRepository = DeliveryRequestRepository.getInstance(deliveryRequestsDao)
}
}
_requests = requestRepository.getRequests()
updateRequests();
}
}
** When creating a repository, I get a type mismatch error: **
requestRepository = PaymentRequestRepository.getInstance(paymentRequestDao)
Tell me how is this done correctly?

Android app retrieve data from server, save in database and display to user

I'm rewriting an app that involves retrieving data from a server via REST, saving that to the database on each Android device, and then displaying that data to the user. The data being retrieved from the server has a "since" parameter, so it won't return all data, just data that has changed since the last retrieval.
I have the retrieval from the server working fine, but I'm not sure the best way to save that data to the database, then show it to the user. I'm using Kotlin, Retrofit, Room and LiveData.
The code below is a simplified version of what I'm actually doing, but it gets the point across.
MyData.kt (model)
#Entity(tableName = "MyTable")
data class MyData(
#PrimaryKey(autoGenerate = true)
#ColumnInfo(name = "id")
var id Int? = null,
#SerializedName("message")
#ColumnInfo(name = "message")
var message: String? = null
) {
companion object {
fun fromContentValues(values: ContentValues): MyData {
val data = MyData()
// Do this for id and message
if (values.containsKey("id") {
data.id = values.getAsInteger("id")
}
}
}
}
DataViewModel.kt
class DataViewModel(application: Application) : AndroidViewModel(application) {
private val repository = DataRepository()
fun data(since: Long) =
liveData(Dispatchers.IO) {
val data = repository.getDataFromServer(since)
emit(data)
}
fun saveData(data: List<MyData>) =
liveData(Dispatchers.Default) {
val result = repository.saveDataToDatabase(data)
emit(result)
}
fun data() =
liveData(Dispatchers.IO) {
val data = repository.getDataFromDatabase()
emit(data)
}
}
DataRepository.kt
class DataRepository(application: Application) {
// I won't add how the Retrofit client is created, it's standard
private var client = "MyUrlToGetDataFrom"
private var myDao: MyDao
init {
val myDatabase = MyDatabase.getDatabase(application)
myDao = myDatabase!!.myDao()
}
suspend fun getDataFromServer(since: Long): List<MyData> {
try {
return client.getData(since)
} catch (e: Exception) {
}
}
fun getDataFromDatabase(): List<MyData> = myDao.getAll()
suspend fun insertData(data: List<MyData>) =
myDao.insertData(data)
}
MyDao.kt
#Dao
interface PostsDao {
#Query("SELECT * FROM " + Post.TABLE_NAME + " ORDER BY " + Post.COLUMN_ID + " desc")
suspend fun getAllData(): List<MyData>
#Insert
suspend fun insertData(data: List<MyData>)
}
ListActivity.kt
private lateinit var mDataViewModel: DataViewModel
override fun onCreate(savedInstanceBundle: Bundle?) {
super.onCreate(savedInstanceBundle)
mDataViewModel = ViewModelProvider(this, DataViewModelFactory(contentResolver)).get(DataViewModel::class.java)
getData()
}
private fun getData() {
mDataViewModel.data(getSince()).observe(this, Observer {
saveData(it)
})
}
private fun saveData(data: List<MyData>) {
mDataViewModel.saveData(data)
mDataViewModel.data().observe(this, Observer {
setupRecyclerView(it)
})
}
ListActivity.kt, and possibly the ViewModel and Repository classes where it uses coroutines, are where I'm stuck. getData() retrieves the data from the server without a problem, but when it comes to saving it in the database, then taking that saved data from the database and displaying it to the user I'm unsure of the approach. As I mentioned I'm using Room, but Room will not let you access the database on the main thread.
Remember, I have to save in the database first, then retrieve from the database, so I don't want to call mDataViewModel.data().observe until after it saves to the database.
What is the proper approach to this? I've tried doing CoroutineScope on the mDataViewModel.saveData() then .invokeOnCompletion to do mDataViewModel.data().observe, but it doesn't save to the database. I'm guessing I'm doing my Coroutines incorrectly, but not sure where exactly.
It will also eventually need to delete and update records from the database.

Updated Answer
After reading comments and updated question I figured out that you want to fetch a small list of data and store it to database and show all the data stored in the database. If this is what you want, you can perform the following (omitted DataSouce for brevity) -
In PostDao You can return a LiveData<List<MyData>> instead of List<MyData> and observe that LiveData in the Activity to update the RecyclerView. Just make sure you remove the suspend keyword as room will take care of threading when it returns LiveData.
#Dao
interface PostsDao {
#Query("SELECT * FROM " + Post.TABLE_NAME + " ORDER BY " + Post.COLUMN_ID + " desc")
fun getAllData(): LiveData<List<MyData>>
#Insert
suspend fun insertData(data: List<MyData>)
}
In Repository make 2 functions one for fetching remote data and storing it to the database and the other just returns the LiveData returned by the room. You don't need to make a request to room when you insert the remote data, room will automatically update you as you are observing a LiveData from room.
class DataRepository(private val dao: PostsDao, private val dto: PostDto) {
fun getDataFromDatabase() = dao.getAllData()
suspend fun getDataFromServer(since: Long) = withContext(Dispatchers.IO) {
val data = dto.getRemoteData(since)
saveDataToDatabase(data)
}
private suspend fun saveDataToDatabase(data: List<MyData>) = dao.insertData(data)
}
Your ViewModel should look like,
class DataViewModel(private val repository : DataRepository) : ViewModel() {
val dataList = repository.getDataFromDatabase()
fun data(since: Long) = viewModelScope.launch {
repository.getDataFromServer(since)
}
}
In the Activity make sure you use ListAdapter
private lateinit var mDataViewModel: DataViewModel
private lateinit var mAdapter: ListAdapter
override fun onCreate(savedInstanceBundle: Bundle?) {
...
mDataViewModel.data(getSince())
mDataViewModel.dataList.observe(this, Observer(adapter::submitList))
}
Initial Answer
First of all, I would recommend you to look into Android Architecture Blueprints v2. According to Android Architecture Blueprints v2 following improvements can be made,
DataRepository should be injected rather than instantiating internally according to the Dependency Inversion principle.
You should decouple the functions in the ViewModel. Instead of returning the LiveData, the data() function can update an encapsulated LiveData. For example,
class DataViewModel(private val repository = DataRepository) : ViewModel() {
private val _dataList = MutableLiveData<List<MyData>>()
val dataList : LiveData<List<MyData>> = _dataList
fun data(since: Long) = viewModelScope.launch {
val list = repository.getData(since)
_dataList.value = list
}
...
}
Repository should be responsible for fetching data from remote data source and save it to local data source. You should have two data source i.e. RemoteDataSource and LocalDataSource that should be injected in the Repository. You can also have an abstract DataSource. Let's see how can you improve your repository,
interface DataSource {
suspend fun getData(since: Long) : List<MyData>
suspend fun saveData(list List<MyData>)
suspend fun delete()
}
class RemoteDataSource(dto: PostsDto) : DataSource { ... }
class LocalDataSource(dao: PostsDao) : DataSource { ... }
class DataRepository(private val remoteSource: DataSource, private val localSource: DataSource) {
suspend fun getData(since: Long) : List<MyData> = withContext(Dispatchers.IO) {
val data = remoteSource.getData(since)
localSource.delete()
localSource.save(data)
return#withContext localSource.getData(since)
}
...
}
In your Activity, you just need to observe the dataList: LiveData and submit it's value to ListAdapter.
private lateinit var mDataViewModel: DataViewModel
private lateinit var mAdapter: ListAdapter
override fun onCreate(savedInstanceBundle: Bundle?) {
...
mDataViewModel.data(since)
mDataViewModel.dataList.observe(this, Observer(adapter::submitList))
}

MVVM return value from Model to Repository

I Am using MVVM architecture to simple project. Then i stack in this case, when i have to return value from Model DataSource (Lambda function) to Repository then ViewModel will observe this repository. Please correct me if this not ideally and give me some advise for the true MVVM in android. i want to use LiveData only instead of RxJava in this case, because many sample in Github using RxJava.
In my Model i have class UserDaoImpl, code snippet like below
class UserDaoImpl : UserDao {
private val resultCreateUser = MutableLiveData<AppResponse>()
private val mAuth : FirebaseAuth by lazy {
FirebaseAuth.getInstance()
}
override fun createUser(user: User) {
mAuth.createUserWithEmailAndPassword(user.email, user.password)
.addOnCompleteListener {
//I DID NOT REACH THIS LINE
println("hasilnya ${it.isSuccessful} ")
if(it.isSuccessful){
val appResponse = AppResponse(true, "oke")
resultCreateUser.postValue(appResponse)
}else{
val appResponse = AppResponse(false, "not oke -> ${it.result.toString()}")
resultCreateUser.postValue(appResponse)
}
}
.addOnFailureListener {
println("hasilnya ${it.message}")
val appResponse = AppResponse(false, "not oke -> ${it.message}")
resultCreateUser.postValue(appResponse)
}
}
override fun getResultCreateUser() = resultCreateUser
}
And this is my Repository snippet code
class RegisterRepositoryImpl private constructor(private val userDao: UserDao) : RegisterRepository{
companion object{
#Volatile private var instance : RegisterRepositoryImpl? = null
fun getInstance(userDao: UserDao) = instance ?: synchronized(this){
instance ?: RegisterRepositoryImpl(userDao).also {
instance = it
}
}
}
override fun registerUser(user: User) : LiveData<AppResponse> {
userDao.createUser(user)
return userDao.getResultCreateUser() as LiveData<AppResponse>
}
}
Then this is my ViewModel
class RegisterViewModel (private val registerRepository: RegisterRepository) : ViewModel() {
val signUpResult = MutableLiveData<AppResponse>()
fun registerUser(user: User){
println(user.toString())
val response = registerRepository.registerUser(user)
signUpResult.value = response.value
}
}
If i execute the snippet code above, the result always nullpointer in signUpResult
This is my Activity
lateinit var viewModel: RegisterViewModel
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_register)
initializeUI()
}
private fun initializeUI() {
val factory = InjectorUtils.provideRegisterViewModelFactory()
viewModel = ViewModelProviders.of(this, factory).get(RegisterViewModel::class.java)
viewModel.signUpResult.observe(this, Observer {
//IT always null
if(it.success){
// to HomeActivity
Toast.makeText(this, "Success! ${it.msg}", Toast.LENGTH_SHORT).show()
}else{
Toast.makeText(this, "FALSE! ${it.msg}", Toast.LENGTH_SHORT).show()
}
})
register_btn.setOnClickListener {
val username = name.text.toString()
val email = email.text.toString()
val password = password.text.toString()
val phone = number.text.toString()
val user = User(0, username,"disana", email, password, "disana")
viewModel.registerUser(user)
}
}
Crash occured when i press register button

I'm not 100% sure, but I think the problem is in your ViewModel, where you are trying to pass by reference MutableLiveData. Your Activity is observing signUpResult MutableLiveData, but you are never posting new value, you are trying to change reference of that LiveData to one in Repository.
val signUpResult = MutableLiveData<AppResponse>()
fun registerUser(user: User){
println(user.toString())
val response = registerRepository.registerUser(user)
signUpResult.value = response.value
}
I think that the solution here is to let your ViewModel return LiveData, which is returned from Repository.
fun registerUser(user: User): MutableLiveData<AppResponse> {
println(user.toString())
return registerRepository.registerUser(user)
}
And you need to observe function registerUser(user) in your Activity.
viewModel.registerUser(user).observe(this, Observer {
But now you encountered another problem. By this example you will trigger observe method every time your button is clicked. So you need to split in repository your function, you need to make one only for returning userDao.getResultCreateUser() as LiveData<AppResponse>, and the other to trigger userDao.create(user) .
So you can make two functions in your repository
override fun observeRegistrationResponse() : LiveData<AppResponse> {
return userDao.getResultCreateUser() as LiveData<AppResponse>
}
override fun registerUser(user: User) {
userDao.createUser(user)
}
Now also in ViewModel you need to make separate function for observing result and for sending request for registration.
fun observeRegistrationResponse(): LiveData<AppResponse> {
return registerRepository.observeRegistrationResponse()
}
fun registerUser(user: User){
println(user.toString())
registerRepository.registerUser(user)
}
And finally you can observe in your function initializeUI
viewModel.observeRegistrationResponse().observe(this, Observer {
And send registration request on button click
viewModel.registerUser(user)
Sorry for long response, but I tried to explain why you need to change your approach. I hope I helped you a bit to understand how LiveData works.