Develop Reference

How to test ViewModel + Flow

I'm doing a small project to learn flow and the latest Android features, and I'm currently facing the viewModel's testing, which I don't know if I'm performing correctly. can you help me with it?
Currently, I am using a use case to call the repository which calls a remote data source that gets from an API service a list of strings.
I have created a State to control the values in the view model:
data class StringItemsState(
val isLoading: Boolean = false,
val items: List<String> = emptyList(),
val error: String = ""
)
and the flow:
private val stringItemsState = StringtemsState()
private val _stateFlow = MutableStateFlow(stringItemsState)
val stateFlow = _stateFlow.asStateFlow()
and finally the method that performs all the logic in the viewModel:
fun fetchStringItems() {
try {
_stateFlow.value = stringItemsState.copy(isLoading = true)
viewModelScope.launch(Dispatchers.IO) {
val result = getStringItemsUseCase.execute()
if (result.isEmpty()) {
_stateFlow.value = stringItemsState
} else {
_stateFlow.value = stringItemsState.copy(items = result)
}
}
} catch (e: Exception) {
e.localizedMessage?.let {
_stateFlow.value = stringItemsState.copy(error = it)
}
}
}
I am trying to perform the test following the What / Where / Then pattern, but the result is always an empty list and the assert verification always fails:
private val stringItems = listOf<String>("A", "B", "C")
#Test
fun `get string items - not empty`() = runBlocking {
// What
coEvery {
useCase.execute()
} returns stringItems
// Where
viewModel.fetchStringItems()
// Then
assert(viewModel.stateFlow.value.items == stringItems)
coVerify(exactly = 1) { viewModel.fetchStringItems() }
}
Can someone help me and tell me if I am doing it correctly? Thanks.

Retrieve data from Android DataStore and save to global var

I am making android app and I wants save configuration in Android DataStore. I have created a class and the values from EditText are correct save to DataStore. I using tutorial from YouTube: https://www.youtube.com/watch?v=hEHVn9ATVjY
I can view the configuration in the config view correctly (textview fields get the value from the datastore):
private fun showConfigurationInForm(){
mainViewModel = ViewModelProvider(this).get(MainViewModel::class.java)
mainViewModel.readMqttAddressFlow.observe(this) { mqqtAdress ->
binding.conMqttAddress.setText(mqqtAdress)
}
}
This function show actual config in EditText, and this is great
But the config I will use to connect to MQTT Server, and how can I save the config to Varchar and use to another function?
I create var in class:
class ConfigurationActivity : AppCompatActivity() {
private lateinit var binding: ActivityConfigurationBinding
private lateinit var mainViewModel: MainViewModel
var variMqttAddress = ""
(...)
And in function getValueFromDatastoreAndSaveToVar I want to get and save values from DataStore to variable variMqttAddress
private fun getValueFromDatastoreAndSaveToVar(){
mainViewModel = ViewModelProvider(this).get(MainViewModel::class.java)
mainViewModel.readMqttAddressFlow.observe(this) { mqqtAdress ->
variMqttAddress = mqqtAdress
}
}
but it doesn't work. when debugging I have an empty value in var
Log.d(TAG, "variMqttAddress:: $variMqttAddress")
___________
2021-02-16 12:42:20.524 12792-12792 D/DEBUG: variMqttAddress::
Please help

When using flows with DataStore, value will be fetched asynchronously meaning you wont have the value right away, try printing log inside observe method and then create your MQttClient with the url
private fun getValueFromDatastoreAndSaveToVar(){
mainViewModel = ViewModelProvider(this).get(MainViewModel::class.java)
mainViewModel.readMqttAddressFlow.observe(this) { mqqtAdress ->
variMqttAddress = mqqtAdress
//varImqttAddress will be available at this point
Log.d(TAG, "variMqttAddress:: $variMqttAddress")
val mqttClient = MqttAsyncClient(varImqttAddress, clientId, MemoryPersistence())
}
}
other way is to use, collect/first on flows for blocking get but it requires to be inside a coroutinescope
Quick Tip: I think you can initialise mainViewModel globally once and access it in all methods instead of reassigning them in each
method. Seems redundant
UPDATE
If you have multiple values coming from different LiveData instances, then you can create a method something like validateParatmers(), which will have checks for all the parameters before creating instance like
private fun getValueFromDatastoreAndSaveToVar(){
mainViewModel = ViewModelProvider(this).get(MainViewModel::class.java)
mainViewModel.readMqttAddressFlow.observe(this) { mqqtAdress ->
variMqttAddress = mqqtAdress
Log.d(TAG, "variMqttAddress:: $variMqttAddress")
validateParametersAndInitMqtt() //add checks after observing ever livedata
}
mainViewModel.readMqttPortFlow.observe(this) {mqttPort ->
variMqttPass = mqttPort.toString()
validateParametersAndInitMqtt()
}
mainViewModel.readMqttUserFlow.observe(this) { mqttUser ->
variMqttUser = mqttUser
validateParametersAndInitMqtt()
}
mainViewModel.readMqttPassFlow.observe(this) { mqttPass ->
variMqttPass = mqttPass
validateParametersAndInitMqtt()
}
}
private fun validateParametersAndInitMqtt(){
if(variMqttAddress.isEmpty() || variMqttPass.isEmpty()
|| variMqttUser.isEmpty() || variMqttPass.isEmpty()){
//if any one is also empty, then don't proceed further
return
}
//create socket instance here, all your values will be available
}

Thank you for your help
I did not add earlier that in addition to the address of the MQQT server in the configuration, it also stores the port, user and password.
I think I am doing something wrong, in every YouTube tutorial it is shown how to "download" one configuration parameter. My function that retrieves data now looks like this:
private fun getValueFromDatastoreAndSaveToVar(){
mainViewModel = ViewModelProvider(this).get(MainViewModel::class.java)
mainViewModel.readMqttAddressFlow.observe(this) { mqqtAdress ->
variMqttAddress = mqqtAdress
Log.d(TAG, "variMqttAddress:: $variMqttAddress")
}
mainViewModel.readMqttPortFlow.observe(this) {mqttPort ->
variMqttPass = mqttPort.toString()
}
mainViewModel.readMqttUserFlow.observe(this) { mqttUser ->
variMqttUser = mqttUser
}
mainViewModel.readMqttPassFlow.observe(this) { mqttPass ->
variMqttPass = mqttPass
}
}
in the repository class, I create a flow for each value
//Create MQTT Address flow
val readMqttAddressFlow: Flow<String> = dataStore.data
.catch { exception ->
if(exception is IOException){
Log.d("DataStore", exception.message.toString())
emit(emptyPreferences())
}else {
throw exception
}
}
.map { preference ->
val mqqtAdress = preference[PreferenceKeys.CON_MQTT_ADDRESS] ?: "none"
mqqtAdress
}
//Create MQTT Port flow
val readMqttPortFlow: Flow<Int> = dataStore.data
.catch { exception ->
if(exception is IOException){
Log.d("DataStore", exception.message.toString())
emit(emptyPreferences())
}else {
throw exception
}
}
.map { preference ->
val mqqtPort = preference[PreferenceKeys.CON_MQTT_PORT] ?: 0
mqqtPort
}
(.....)
now the question is am I doing it right?
now how to create MQttClient only when I have all parameters in variables?
can do some sleep of the function that is supposed to create the MQQTClient until the asychnronic function assigns values to variables?

How to observe data inside viewmodel?

I have connect my android application to firebase and am using it to retrieve Authentication details and data from firestone. I am using an MVVM architecture and live data for this. The problem is that I need to retrieve email address first and then used this data to query the firestone which contain documents with ID = emailID. You can see my viewmodel. The value for the emailID is null when every I run this. How can I accomplish this while following the MVVP style of coding ?
#Edit: I need to understand how can check if the live data has been initialised with a value in the case where one livedata value depends on the other.
class ProfileViewModel(): ViewModel() {
var random =""
private var _name = MutableLiveData<String>()
val userName
get()=_name
private var _post = MutableLiveData<String>()
val userPost
get()=_post
private var _imgUrl = MutableLiveData<Uri>()
val userImgUrl
get()=_imgUrl
private var _emailId = MutableLiveData<String>()
val userEmailId
get()=_emailId
init{
getUserDataFromProfile()
getUserPostFromFirestone()
}
private fun getUserPostFromFirestone() {
val mDatabaseInstance: FirebaseFirestore = FirebaseFirestore.getInstance()
// _emailId.observe(getApplication(), Observer {
//
// } )
if(_emailId.value!=null){
mDatabaseInstance.collection("users").document(_emailId.value)
.get()
.addOnCompleteListener { task ->
if (task.isSuccessful) {
_post.value = task.result?.data?.get("post").toString()
} else {
// Log.w("firestone", "Error getting documents.", task.exception)
_post.value = "Unable to Retrieve"
}
}
}
}
private fun getUserDataFromProfile() {
val mAuth = FirebaseAuth.getInstance()
val currentUser = mAuth.currentUser
random = currentUser?.displayName!!
_name.value = currentUser?.displayName
_post.value = "Unknown"
_imgUrl.value = currentUser?.photoUrl
_emailId.value = currentUser?.email
}
}

If you write a wrapper over the Firebase call and expose it as a LiveData (or, in this case, I'll pretend it's wrapped in a suspendCoroutineCancellable), in which case whenever you want to chain stuff, you either need MediatorLiveData to combine multiple LiveDatas into a single stream (see this library I wrote for this specific purpose) or just switchMap.
private val auth = FirebaseAuth.getInstance()
val imgUrl: LiveData<Uri> = MutableLiveData<Uri>(auth.currentUser?.photoUrl)
val emailId: LiveData<String> = MutableLiveData<String>(auth.currentUser?.email)
val post = emailId.switchMap { emailId ->
liveData {
emit(getUserByEmailId(emailId))
}
}

you can set observer to LiveData and remove it when you don't need it:
class ProfileViewModel : ViewModel() {
private val _email = MutableLiveData<String>()
private val emailObserver = Observer<String> { email ->
//email is here
}
init {
_email.observeForever(emailObserver)
}
override fun onCleared() {
_email.removeObserver(emailObserver)
super.onCleared()
}
}

Try using coroutines for the sequential execution of the code. so once you get the output of one and then the second one starts executing. If this isnt working Please let me know i can try help you.
init{
viewModelScope.launch{
getUserDataFromProfile()
getUserPostFromFirestone()
}
}

ExoPlayer problems trying to download current track

I am using Exoplayer to create my own music player. I am also adding the option to download the track but I have a problem when I am trying to download the track that I am playing. I add a notification to the download to check the progress of the download and it appears but it even doesn't start. What I think is that it might have some kind of problem with the buffering cache and the download since they are stored in the same folder.
To download the tracks I do the following:
override fun addDownloadTrack(track: Track) {
getIfTrackIsCached.run({ isCached ->
if (!isCached) {
val data = Util.toByteArray(track.title.byteInputStream())
val downloadRequest =
DownloadRequest(track.id, DownloadRequest.TYPE_PROGRESSIVE, Uri.parse(track.href), Collections.emptyList(), track.id, data)
DownloadService.sendAddDownload(context, ExoPlayerDownloadService::class.java, downloadRequest, false)
}
}, ::onError, GetIfTrackIsCached.Params(track.id))
}
This is the DownloadService:
class ExoPlayerDownloadService : DownloadService(
FOREGROUND_NOTIFICATION_ID,
DEFAULT_FOREGROUND_NOTIFICATION_UPDATE_INTERVAL,
Constants.CHANNEL_DOWNLOAD_ID,
R.string.exo_download_notification_channel_name) {
private val manager: DownloadManager by inject()
private val channelIsCached: ChannelPublisher<CachedMedia> by inject(PUBLISHER_IS_CACHED)
private val notificationHelper: DownloadNotificationHelper by inject()
private var nextNotificationId: Int = FOREGROUND_NOTIFICATION_ID
override fun onCreate() {
super.onCreate()
if (!manager.isInitialized) {
manager.maxParallelDownloads = MAX_PARALLEL_DOWNLOADS
}
}
override fun getDownloadManager(): DownloadManager = manager
override fun getForegroundNotification(downloads: MutableList<Download>?): Notification {
var text = ""
var index = 1
downloads?.forEach { text += "${if (downloads.size > 1) "${index++} - " else ""}${Util.fromUtf8Bytes(it.request.data)}\n" }
return notificationHelper.buildProgressNotification(R.drawable.ic_stat_downloading, null, text, downloads)
}
override fun getScheduler(): Scheduler? = null
override fun onDownloadChanged(download: Download?) {
val notification = when (download?.state) {
Download.STATE_COMPLETED -> {
channelIsCached.publish(CachedMedia(download.request.id, true))
notificationHelper.buildDownloadCompletedNotification(R.drawable.ic_stat_download_complete, null, Util.fromUtf8Bytes(download.request.data))
}
Download.STATE_FAILED ->
notificationHelper.buildDownloadFailedNotification(R.drawable.ic_stat_download_failed, null, Util.fromUtf8Bytes(download.request.data))
else -> null
}
notification?.let { NotificationUtil.setNotification(this#ExoPlayerDownloadService, ++nextNotificationId, it) }
}
companion object {
private const val MAX_PARALLEL_DOWNLOADS = 3
private const val FOREGROUND_NOTIFICATION_ID = 2000
}
}
And to create the cache I use this:
SimpleCache(File(androidContext().cacheDir, CACHE_MEDIA_FOLDER), NoOpCacheEvictor(), get<DatabaseProvider>())
How can I avoid conflicts between buffering cache and downloaded files?

I had this issue also, and found the solution!
The downloading documentation states
The CacheDataSource.Factory should be configured as read-only to avoid downloading that content as well during playback.
To do this you must call setCacheWriteDataSinkFactory(null) on your CacheDataSource.Factory object.
This will prevent the stream from writing to the cache, allowing the downloader to write as expected.

Blocking the Application class via runBlocking kotlin

I have a confusion about how Dispatchers work in Kotlin
Task
In my Application class I intend to access my database via Room, take out the user , take out his JWT accessToken and set it in another object that my retrofit Request inteceptor uses.
However I want all this code to be blocking , so that when the Application class has ran to its completion , the user has been extracted and set in the Inteceptor.
Problem
My application class runs to completion BEFORE the user has been picked from the database.
Session class is the one which accesses Room
This is how my session class looks
class Session(private val userRepository: UserRepository, private var requestHeaders: RequestHeaders) {
var authenticationState: AuthenticationState = AuthenticationState.UNAUTHENTICATED
var loggedUser: User? by Delegates.observable<User?>(null) { _, _, user ->
if (user != null) {
user.run {
loggedRoles = roleCsv.split(",")
loggedRoles?.run {
if (this[0] == "Employer") {
employer = toEmployer()
} else if (this[0] == "Employee") {
employee = toEmployee()
}
}
authenticationState = AuthenticationState.AUTHENTICATED
requestHeaders.accessToken = accessToken
}
} else {
loggedRoles = null
employer = null
employee = null
authenticationState = AuthenticationState.UNAUTHENTICATED
requestHeaders.accessToken = null
}
}
var loggedRoles: List<String>? = null
var employee: Employee? = null
var employer: Employer? = null
init {
runBlocking(Dispatchers.IO) {
loggedUser = userRepository.loggedInUser()
Log.d("Session","User has been set")
}
}
// var currentCity
// var currentLanguage
}
enum class AuthenticationState {
AUTHENTICATED, // Initial state, the user needs to secretQuestion
UNAUTHENTICATED, // The user has authenticated successfully
LOGGED_OUT, // The user has logged out.
}
This is my Application class
class MohreApplication : Application()
{
private val session:Session by inject()
private val mohreDatabase:MohreDatabase by inject() // this is integral. Never remove this from here. This seeds the data on database creation
override fun onCreate() {
super.onCreate()
startKoin {
androidLogger()
androidContext(this#MohreApplication)
modules(listOf(
platformModule,
networkModule,
....
))
}
Log.d("Session","Launching application")
}
My Koin module which creates the session
val platformModule = module {
// single { Navigator(androidApplication()) }
single { Session(get(),get()) }
single { CoroutineScope(Dispatchers.IO + Job()) }
}
In my Logcat first "Launching Application" prints out and THEN "User has been set"
Shouldn't it be reverse? . This is causing my application to launch without the Session having the user and my MainActivity complains.

by inject() is using kotlin lazy initialization. Only when session.loggedUser is queried will the init block be fired.
In your case, when you call session.loggedUser in the MainActivity, the init block will fire and block the calling thread.
What you can do is.
import org.koin.android.ext.android.get
class MohreApplication : Application()
{
private lateinit var session: Session
private lateinit var mohreDatabase: MohreDatabase // this is integral. Never remove this from here. This seeds the data on database creation
override fun onCreate() {
super.onCreate()
startKoin {
androidLogger()
androidContext(this#MohreApplication)
modules(listOf(
platformModule,
networkModule,
....
))
}
session = get()
mohreDatabase = get()
Log.d("Session","Launching application")
}