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Cannot create an instance of class ViewModel unable to find cause

whenever I click on the title, the app Crashes shows this logcat
I am new to Android
using
dagger hilt,
exoplayer,
this is where i touch got error:
Songfragment
#AndroidEntryPoint
class SongFragments : Fragment(R.layout.fragment_song) {
#Inject
lateinit var glide: RequestManager
private lateinit var mainViewModel: MainViewModel
private val songViewModel: SongViewModel by viewModels()
private var curplayingSong: sound? = null
private var playbackState: PlaybackStateCompat? = null
private var shouldUpdateSeekbar = true
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
mainViewModel = ViewModelProvider(requireActivity()).get(MainViewModel::class.java)
subscribeToObservers()
ivPlayPauseDetail.setOnClickListener {
curplayingSong?.let {
mainViewModel.playOrToggleSound(it, true)
}
}
seekBar.setOnSeekBarChangeListener(object : SeekBar.OnSeekBarChangeListener {
override fun onProgressChanged(seekBar: SeekBar?, progress: Int, fromUser: Boolean) {
if (fromUser) {
setCurPlayerTimeToTextView(progress.toLong())
}
}
override fun onStartTrackingTouch(seekBar: SeekBar?) {
shouldUpdateSeekbar = false
}
override fun onStopTrackingTouch(seekBar: SeekBar?) {
seekBar?.let {
mainViewModel.seekTo(it.progress.toLong())
shouldUpdateSeekbar = true
}
}
})
ivSkipPrevious.setOnClickListener {
mainViewModel.skipToPreviousSound()
}
ivSkip.setOnClickListener{
mainViewModel.skipToNextSound()
}
}
private fun updateTitleAndSongImage(sound: sound) {
val title = "${sound.title} - ${sound.subtitle}"
tvSongName.text = title
glide.load(sound.imageUrl).into(ivSongImage)
}
private fun subscribeToObservers() {
mainViewModel.mediaItems.observe(viewLifecycleOwner){
it?.let { result ->
when(result.status){
Status.SUCCESS -> {
result.data?.let { sounds ->
if (curplayingSong == null && sounds.isNotEmpty()) {
curplayingSong = sounds[0]
updateTitleAndSongImage(sounds[0])
}
}
}
else -> Unit
}
}
}
mainViewModel.curPlayingSound.observe(viewLifecycleOwner) {
if(it == null) return#observe
curplayingSong = it.toSong()
updateTitleAndSongImage(curplayingSong!!)
}
mainViewModel.playbackState.observe(viewLifecycleOwner) {
playbackState = it
ivPlayPauseDetail.setImageResource(
if (playbackState?.isPlaying == true) R.drawable.ic_pause else R.drawable.ic_play
)
seekBar.progress = it?.position?.toInt() ?: 0
}
songViewModel.curPlayerPosition.observe(viewLifecycleOwner) {
if (shouldUpdateSeekbar) {
seekBar.progress = it.toInt()
setCurPlayerTimeToTextView(it)
}
}
songViewModel.curSongDuration.observe(viewLifecycleOwner) {
seekBar.max = it.toInt()
val dateFormat = SimpleDateFormat("mm:ss", Locale.getDefault())
tvSongDuration.text = dateFormat.format(it)
}
}
private fun setCurPlayerTimeToTextView(ms: Long) {
val dateFormat = SimpleDateFormat("mm:ss", Locale.getDefault())
tvCurTime.text = dateFormat.format(ms)
}
}
SongviewModel
class SongViewModel #ViewModelInject constructor(
musicServiceConnection: MusicServiceConnection
) : ViewModel() {
private val playbackState = musicServiceConnection.playBackState
private val _curSongDuration = MutableLiveData<Long>()
val curSongDuration: LiveData<Long> = _curSongDuration
private val _curPlayerPosition = MutableLiveData<Long>()
val curPlayerPosition: LiveData<Long> = _curPlayerPosition
init {
updateCurrentplayerPostion()
}
#SuppressLint("NullSafeMutableLiveData")
private fun updateCurrentplayerPostion() {
viewModelScope.launch {
while(true) {
val pos = playbackState.value?.currentPlaybackPosition
if(curPlayerPosition.value != pos){
_curPlayerPosition.postValue(pos)
_curSongDuration.postValue(MusicService.curSoundDuration)
}
delay(UPDATE_PLAYER_POSITION_INTERVAL)
}
}
}
}
logcat:
2022-08-12 19:11:39.122 10888-10983/com.fridayhouse.snoozz E/ion: ioctl c0044901 failed with code -1: Invalid argument
2022-08-12 19:11:39.318 10888-10888/com.fridayhouse.snoozz E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.fridayhouse.snoozz, PID: 10888
java.lang.RuntimeException: Cannot create an instance of class com.fridayhouse.snoozz.ui.viewmodels.SongViewModel
at androidx.lifecycle.ViewModelProvider$NewInstanceFactory.create(ViewModelProvider.kt:204)
at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.kt:322)
at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.kt:304)
at androidx.lifecycle.SavedStateViewModelFactory.create(SavedStateViewModelFactory.kt:175)
at androidx.lifecycle.SavedStateViewModelFactory.create(SavedStateViewModelFactory.kt:203)
at dagger.hilt.android.internal.lifecycle.HiltViewModelFactory.create(HiltViewModelFactory.java:111)
at androidx.lifecycle.ViewModelProvider$Factory.create(ViewModelProvider.kt:83)
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.kt:187)
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.kt:153)
at androidx.lifecycle.ViewModelLazy.getValue(ViewModelLazy.kt:53)
at androidx.lifecycle.ViewModelLazy.getValue(ViewModelLazy.kt:35)
at com.fridayhouse.snoozz.ui.fragments.SongFragments.getSongViewModel(SongFragments.kt:33)
at com.fridayhouse.snoozz.ui.fragments.SongFragments.subscribeToObservers(SongFragments.kt:121)
at com.fridayhouse.snoozz.ui.fragments.SongFragments.onViewCreated(SongFragments.kt:45)
at androidx.fragment.app.Fragment.performViewCreated(Fragment.java:3128)
at androidx.fragment.app.FragmentStateManager.createView(FragmentStateManager.java:552)
at androidx.fragment.app.FragmentStateManager.moveToExpectedState(FragmentStateManager.java:261)
at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:1890)
at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:1814)
at androidx.fragment.app.FragmentManager.execPendingActions(FragmentManager.java:1751)
at androidx.fragment.app.FragmentManager$5.run(FragmentManager.java:538)
at android.os.Handler.handleCallback(Handler.java:938)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loopOnce(Looper.java:233)
at android.os.Looper.loop(Looper.java:334)
at android.app.ActivityThread.main(ActivityThread.java:8396)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:582)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1068)
Caused by: java.lang.InstantiationException: java.lang.Class<com.fridayhouse.snoozz.ui.viewmodels.SongViewModel> has no zero argument constructor
at java.lang.Class.newInstance(Native Method)
at androidx.lifecycle.ViewModelProvider$NewInstanceFactory.create(ViewModelProvider.kt:202)
at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.kt:322) 
at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.kt:304) 
at androidx.lifecycle.SavedStateViewModelFactory.create(SavedStateViewModelFactory.kt:175) 
at androidx.lifecycle.SavedStateViewModelFactory.create(SavedStateViewModelFactory.kt:203) 
at dagger.hilt.android.internal.lifecycle.HiltViewModelFactory.create(HiltViewModelFactory.java:111) 
at androidx.lifecycle.ViewModelProvider$Factory.create(ViewModelProvider.kt:83) 
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.kt:187) 
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.kt:153) 
at androidx.lifecycle.ViewModelLazy.getValue(ViewModelLazy.kt:53) 
at androidx.lifecycle.ViewModelLazy.getValue(ViewModelLazy.kt:35) 
at com.fridayhouse.snoozz.ui.fragments.SongFragments.getSongViewModel(SongFragments.kt:33) 
at com.fridayhouse.snoozz.ui.fragments.SongFragments.subscribeToObservers(SongFragments.kt:121) 
at com.fridayhouse.snoozz.ui.fragments.SongFragments.onViewCreated(SongFragments.kt:45) 
at androidx.fragment.app.Fragment.performViewCreated(Fragment.java:3128) 
at androidx.fragment.app.FragmentStateManager.createView(FragmentStateManager.java:552) 
at androidx.fragment.app.FragmentStateManager.moveToExpectedState(FragmentStateManager.java:261) 
at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:1890) 
at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:1814) 
at androidx.fragment.app.FragmentManager.execPendingActions(FragmentManager.java:1751) 
at androidx.fragment.app.FragmentManager$5.run(FragmentManager.java:538) 
at android.os.Handler.handleCallback(Handler.java:938) 
at android.os.Handler.dispatchMessage(Handler.java:99) 
at android.os.Looper.loopOnce(Looper.java:233) 
at android.os.Looper.loop(Looper.java:334) 
at android.app.ActivityThread.main(ActivityThread.java:8396) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:582) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1068) 

#ViewModelInject has been deprecated. You can check here for more info.
In newer versions, You need to annotate viewmodel class with #AndroidViewModel and constructor with #Inject.
#AndroidViewModel
class SongViewModel #Inject constructor(
musicServiceConnection: MusicServiceConnection
) : ViewModel()
Hope it would solve this issue.

Since you are using Hilt, you shouldn't be using by viewModels(). You should set up your MusicServiceConnection in your Provider, and instead of using private val songViewModel: SongViewModel by viewModels(), use #Inject private lateinit var songViewModel: SongViewModel.
I'm not very familiar with Hilt, so I can't provide more guidance. The below is an explanation of what's going wrong with by viewModels(), and how you would resolve this if you were not using a dependency injection framework.
When you create a ViewModel in your Activity or Fragment, you can supply a factory that is responsible for creating instances of the ViewModel. If you don't supply a factory, then the default factory is used.
The default factory is only capable of creating instances of your ViewModel if your ViewModel constructor's arguments are one of the following:
constructor() Empty constructor (no arguments)
constructor(savedStateHandle: SavedStateHandle)
constructor(application: Application)
constructor(application: Application, savedStateHandle: SavedStateHandle)
I don't think this is documented very well. I had to look at the Jetpack source code to learn it.
Since your ViewModel needs a MusicServiceConnection parameter, you cannot use the default factory. You will need to supply an explicit ViewModelProvider.Factory to the by viewModels() as an argument.
This training has an example of creating a ViewModelProvider.Factory class for a ViewModel that needs a special argument for the constructor. In your case, the solution might look like this:
class SongViewModelFactory(private val musicServiceConnection: MusicServiceConnection) : ViewModelProvider.Factory {
override fun <T : ViewModel> create(modelClass: Class<T>): T {
require(modelClass.isAssignableFrom(SongViewModel::class.java)) { "Unknown ViewModel class" }
#Suppress("UNCHECKED_CAST")
return SongViewModel(musicServiceConnection) as T
}
}
I don't know where your MusicServiceConnection class comes from, but let's pretend you can simply instantiate it one time for your Activity with an empty constructor. Then you would replace
private val songViewModel: SongViewModel by viewModels()
with
private val songViewModel: SongViewModel by viewModels {
SongViewModelFactory(MusicServiceConnection())
}
Notice that you are passing a lambda function to viewModels instead of directly passing an instance of your factory. This is because the factory is lazily created only one time, even if your Activity is recreated multiple times (like if the user rotates the screen back and forth). The code inside this lambda is only called once when the app navigates to this screen, even if the Activity is recreated for screen rotations or other configuration changes.

Android paging 3 library removing .cahcedIn(viewModelScope) will throw exception

I am working with paging 3.0.0-alpha11 library in my app.
There is a fragment that has a view model. in the view model I implemented paging data like this. there is one mutable live data for a parameter named promoId. promoId is a string that represents id of a model. i use it with another parameter named page to get a page of data from network. so the problem is that the first time i navigate to te fragment every thing works fine, but after popping the fragment and navigating to it for the second time, I get an error and app crashes.
my fragment code.
class ExploreFragment : DaggerFragment() {
private var _binding: FragmentExploreBinding? = null
private val binding get() = _binding!!
#Inject
lateinit var viewModelProviderFactory: ViewModelProviderFactoryImpl
private lateinit var exploreViewModel: ExploreViewModel
lateinit var commentsAdapter: LiveCommentAdapter
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
initLists()
}
override fun onActivityCreated(savedInstanceState: Bundle?) {
super.onActivityCreated(savedInstanceState)
exploreViewModel =
ViewModelProvider(this, viewModelProviderFactory)[ExploreViewModel::class.java]
observeComments()
commentsViewModel.getPromoComments(promoId)
}
}
private fun initLists() {
commentsAdapter = LiveCommentAdapter()
binding.rvComments.adapter = commentsAdapter
binding.rvSearchResults.adapter = searchResultAdapter
}
private fun observeComments() {
exploreViewModel.commentsLiveData.observe(viewLifecycleOwner) { comments ->
commentsAdapter.submitData(viewLifecycleOwner.lifecycle, comments)
}
}
override fun onDestroyView() {
super.onDestroyView()
_binding = null
}
}
This is my view model
also note that I don't use cachedIn(viewModelScope) after commentRepository.getCommentsByPromo(promoId?:"") because it caches the data and does not call load method of paging data for the second time.
class ExploreViewModel #Inject constructor(
#Inject #JvmField var commentRepository: CommentRepository,
) :
ViewModel() {
private val promoIdLiveData: MutableLiveData<String?> = MutableLiveData()
var commentsLiveData: LiveData<PagingData<Comment>> = promoIdLiveData.switchMap { promoId ->
commentRepository.getCommentsByPromo(promoId?:"")
}
fun getComments(promoId: String) {
promoIdLiveData.value = promoId
}
}
And this is my repository code.
class CommentRepository #Inject constructor(#Inject #JvmField var retrofit: Retrofit) {
private val api: CommentsApi = retrofit.create(CommentsApi::class.java)
fun getCommentsByPromo(promoId: String):LiveData<PagingData<Comment>> = Pager(
config = PagingConfig(pageSize = 20, enablePlaceholders = false,prefetchDistance = 100),
pagingSourceFactory = { PromoCommentPagingSource(promoId, api) }
).liveData
}
and the error i get is
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.tivasoft.project, PID: 28896
java.lang.IllegalStateException: Attempt to collect twice from pageEventFlow, which is an illegal operation. Did you forget to call Flow<PagingData<*>>.cachedIn(coroutineScope)?
at androidx.paging.PageFetcherSnapshot$pageEventFlow$1.invokeSuspend(PageFetcherSnapshot.kt:88)
at androidx.paging.PageFetcherSnapshot$pageEventFlow$1.invoke(Unknown Source:10)
at androidx.paging.CancelableChannelFlowKt$cancelableChannelFlow$1.invokeSuspend(CancelableChannelFlow.kt:35)
at androidx.paging.CancelableChannelFlowKt$cancelableChannelFlow$1.invoke(Unknown Source:10)
at kotlinx.coroutines.flow.ChannelFlowBuilder.collectTo$suspendImpl(Builders.kt:344)
at kotlinx.coroutines.flow.ChannelFlowBuilder.collectTo(Unknown Source:0)
at kotlinx.coroutines.flow.internal.ChannelFlow$collectToFun$1.invokeSuspend(ChannelFlow.kt:60)
at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:106)
at kotlinx.coroutines.EventLoop.processUnconfinedEvent(EventLoop.common.kt:69)
at kotlinx.coroutines.internal.DispatchedContinuationKt.resumeCancellableWith(DispatchedContinuation.kt:349)
at kotlinx.coroutines.intrinsics.CancellableKt.startCoroutineCancellable(Cancellable.kt:30)
at kotlinx.coroutines.intrinsics.CancellableKt.startCoroutineCancellable$default(Cancellable.kt:27)
at kotlinx.coroutines.CoroutineStart.invoke(CoroutineStart.kt:109)
at kotlinx.coroutines.AbstractCoroutine.start(AbstractCoroutine.kt:158)
at kotlinx.coroutines.BuildersKt__Builders_commonKt.launch(Builders.common.kt:56)
at kotlinx.coroutines.BuildersKt.launch(Unknown Source:1)
at kotlinx.coroutines.BuildersKt__Builders_commonKt.launch$default(Builders.common.kt:49)
at kotlinx.coroutines.BuildersKt.launch$default(Unknown Source:1)
at androidx.paging.AsyncPagingDataDiffer.submitData(AsyncPagingDataDiffer.kt:156)
at androidx.paging.PagingDataAdapter.submitData(PagingDataAdapter.kt:172)
at com.tivasoft.project.ui.explore.ExploreFragment$observeComments$$inlined$observe$1.onChanged(LiveData.kt:52)
at androidx.lifecycle.LiveData.considerNotify(LiveData.java:131)
at androidx.lifecycle.LiveData.dispatchingValue(LiveData.java:144)
at androidx.lifecycle.LiveData$ObserverWrapper.activeStateChanged(LiveData.java:443)
at androidx.lifecycle.LiveData$LifecycleBoundObserver.onStateChanged(LiveData.java:395)
at androidx.lifecycle.LifecycleRegistry$ObserverWithState.dispatchEvent(LifecycleRegistry.java:361)
at androidx.lifecycle.LifecycleRegistry.forwardPass(LifecycleRegistry.java:300)
at androidx.lifecycle.LifecycleRegistry.sync(LifecycleRegistry.java:339)
at androidx.lifecycle.LifecycleRegistry.moveToState(LifecycleRegistry.java:145)
at androidx.lifecycle.LifecycleRegistry.handleLifecycleEvent(LifecycleRegistry.java:131)
at androidx.fragment.app.FragmentViewLifecycleOwner.handleLifecycleEvent(FragmentViewLifecycleOwner.java:51)
at androidx.fragment.app.Fragment.performStart(Fragment.java:2737)
at androidx.fragment.app.FragmentStateManager.start(FragmentStateManager.java:365)
at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1194)
at androidx.fragment.app.FragmentManager.addAddedFragments(FragmentManager.java:2224)
at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:1997)
at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:1953)
at androidx.fragment.app.FragmentManager.execPendingActions(FragmentManager.java:1849)
at androidx.fragment.app.FragmentManager$4.run(FragmentManager.java:413)
at android.os.Handler.handleCallback(Handler.java:883)
at android.os.Handler.dispatchMessage(Handler.java:100)
at android.os.Looper.loop(Looper.java:214)
at android.app.ActivityThread.main(ActivityThread.java:7356)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
I would be very thankful if anybody can tell me what's wrong

I'm a bit confused on exactly what you want to happen, but my understanding is that you want to reload from scratch whenever you navigate back.
The error is saying you cannot call .submitData on the same instance of PagingData twice. You're essentially trying load cached data unintentionally and since you didn't call cachedIn, Paging is throwing an exception.
An easy way to force Paging to load from scratch every time, is to make sure you construct a new instance of Pager each time.
So I would try calling observeComments() in onViewCreated and turn commentsLiveData into a function (instead of a var) which returns a new LiveData<PagingData> each time its called.

In my case I had a Transformations.switchMap(liveData) and that was causing the issue, the fix was to make the PagingData to cache before the switchMap
fun observable(): LiveData<PagingData<SomeModel>> {
val pagingData = //obtained somewhere
//make sure to cache it
val chachedPagingData = pagingData.cachedIn(viewModelScope)
return Transformations.switchMap(otherLiveData) { observed ->
//use observed for obtaining live attributes needed
chachedPagingData.filter {...}.map{...}
}
}
For me, that was the solution because the pagingData sometimes can be suspend, so the above would be more explanatory like this:
suspend fun observable(): LiveData<PagingData<SomeModel>> {
val someAttributeFromTheDb = //get it using ROOM
val pagingData = if (someAttributeFromTheDb == /*condition*/) {
suspendPagingData } else regularPagingData
val chachedPagingData = ...
}

Just replace MutableLiveData
private val promoIdLiveData: MutableLiveData<String?> = MutableLiveData()
with SingleLiveEvent
private val promoIdLiveData: SingleLiveEvent<String?> = SingleLiveEvent()
The SingleLiveEvent
class SingleLiveEvent<T> : MutableLiveData<T>() {
private val pending = AtomicBoolean(false)
#MainThread
override fun observe(owner: LifecycleOwner, observer: Observer<in T>) {
if (hasActiveObservers()) {
Log.w(TAG, "Multiple observers registered but only one will be notified of changes.")
}
// Observe the internal MutableLiveData
super.observe(
owner,
Observer { t ->
if (pending.compareAndSet(true, false)) {
observer.onChanged(t)
}
}
)
}
#MainThread
override fun setValue(t: T?) {
pending.set(true)
super.setValue(t)
}
/**
* Used for cases where T is Void, to make calls cleaner.
*/
#MainThread
fun call() {
value = null
}
companion object {
private val TAG = "SingleLiveEvent"
}
}

: kotlin.UninitializedPropertyAccessException: lateinit property manager has not been initialized

I am developing news and I am getting following nullpointexception
java.lang.RuntimeException: Unable to start activity ComponentInfo{yodgorbek.komilov.musobaqayangiliklari/yodgorbek.komilov.musobaqayangiliklari.ui.WelcomeActivity}: kotlin.UninitializedPropertyAccessException: lateinit property manager has not been initialized
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2976)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3113)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:113)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:71)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1858)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:201)
at android.app.ActivityThread.main(ActivityThread.java:6820)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:547)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:922)
Caused by: kotlin.UninitializedPropertyAccessException: lateinit property manager has not been initialized
at yodgorbek.komilov.musobaqayangiliklari.ui.WelcomeActivity.onCreate(WelcomeActivity.kt:26)
at android.app.Activity.performCreate(Activity.java:7224)
at android.app.Activity.performCreate(Activity.java:7213)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1272)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2956)
... 11 more
below my WelcomeActivity.kt class
class WelcomeActivity : AppIntro() {
private lateinit var manager: PreferencesManager
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
// Make sure you don't call setContentView!
if (manager.isFirstRun()) {
showIntroSlides()
} else {
goToMain()
}
}
// Call addSlide passing your Fragments.
// You can use AppIntroFragment to use a pre-built fragment
private fun showIntroSlides() {
manager.setFirstRun()
addSlide(
AppIntroFragment.newInstance(
title = "Welcome to the NewsApp",
description = "NewsApp give your information about life news around the world",
imageDrawable = R.drawable.news,
backgroundDrawable = R.drawable.news_slider,
titleColor = Color.YELLOW,
descriptionColor = Color.RED,
backgroundColor = Color.BLUE,
titleTypefaceFontRes = R.font.opensans_light,
descriptionTypefaceFontRes = R.font.opensans_regular
)
)
addSlide(
AppIntroFragment.newInstance(
title = "...Let's get started!",
description = "This is the last slide, I won't annoy you more :)"
)
)
}
private fun goToMain() {
startActivity(Intent(this, MainActivity::class.java))
}
override fun onSkipPressed(currentFragment: Fragment?) {
super.onSkipPressed(currentFragment)
goToMain()
}
override fun onDonePressed(currentFragment: Fragment?) {
super.onDonePressed(currentFragment)
goToMain()
}
override fun onSlideChanged(oldFragment: Fragment?, newFragment: Fragment?) {
super.onSlideChanged(oldFragment, newFragment)
Log.d("Hello", "Changed")
}
}
I don't understand what is the causing null pointer exception even I have tried initialize manager following way
private var manager: PreferencesManager? = null
but it did not solve my problem
I want to know where I am making mistake what I have to do avoid nullpointer exception

It's simple by looking into logs. Your manager is not initialized before using. Look at onCreate
private lateinit var manager: PreferencesManager
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
// Make sure you don't call setContentView!
// <<<<<<<<<<<<<<< INITIALISE manager HERE >>>>>>>>>>>>>>
if (manager.isFirstRun()) { <<<<<<<< HERE you are using an uninitilised manager
showIntroSlides()
} else {
goToMain()
}
}
Initialise manager before if (manager.isFirstRun()) { in onCreate()

LiveData object Observer never gets called

I have an Activity that has a fragment with a viewmodel in it. The Activity needs to be able to update the livedata object's value as well as does the fragment.
I declared my ViewModel for the fragment like this:
class BottomNavViewModel:ViewModel() {
var isConnected = MutableLiveData<Boolean>()
}
In the BottomNavFragment I have this code to declare the ViewModel
private val viewModel: BottomNavViewModel by lazy { ViewModelProviders.of(this).get(BottomNavViewModel::class.java) }
A few lines below that I have this:
private val changeObserver = Observer<Boolean> { value ->
value?.let {
Timber.i("Update of isConnected received. Updating text field now")
if(it) {
connectedText.text = getString(R.string.connected)
connectedText.setTextColor(activity!!.getColor(R.color.colorSelectedGreen))
}
else {
connectedText.text = getString(R.string.not_connected)
connectedText.setTextColor(activity!!.getColor(R.color.off_red))
}
}
...
override fun onAttach(context: Context) {
super.onAttach(context)
if (context is BottomNavFragment.OnFragmentInteractionListener) {
listener = context
}
else {
throw RuntimeException(context.toString() + " must implement OnFragmentInteractionListener")
}
viewModel.isConnected.observe(this, changeObserver)
}
That Observer never, ever, gets hit.
In my Activity I have this:
private var sharedBottomNavViewModel:BottomNavViewModel? = null
...
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_connection)
sharedBottomNavViewModel = ViewModelProviders.of(this).get(BottomNavViewModel::class.java)
...
override fun onResume() {
super.onResume()
startBackgroundThread()
checkCameraPermission()
//TODO: Change this to listen for a connection
sharedBottomNavViewModel?.let {
Timber.i("Updating isConnected to true now")
it.isConnected.value = true
}
}
In the logs I see the messages indicating that the update occurs but the observer never gets the message.
Can anyone tell me what I am doing wrong here please?

Your 2 viewmodels are not the same. You are creating a viewmodel and passing the lifecycle owner, and in one case you specify the fragment, and in the other the activity.
Change your fragment like this:
private val viewModel: BottomNavViewModel by lazy { ViewModelProviders.of(activity).get(BottomNavViewModel::class.java) }
Be careful where you initialize the viewmodel though, as activity (getActivity()) is nullable.
Edit: (credit Ian Lake) Or, if you use the fragment-ktx artifacts, you can do this
private val viewModel: BottomNavViewModel by activityViewModels()

I Got rarely happens Can't access ViewModels from onDestroy

I got an error like this after launch the app, and that very rarely happens.
Here my complete Java stack trace associated:
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.mycompany.myapp.dev, PID: 11145
java.lang.IllegalStateException: Can't access ViewModels from onDestroy
at android.arch.lifecycle.HolderFragment$HolderFragmentManager.findHolderFragment(HolderFragment.java:136)
at android.arch.lifecycle.HolderFragment$HolderFragmentManager.holderFragmentFor(HolderFragment.java:155)
at android.arch.lifecycle.HolderFragment.holderFragmentFor(HolderFragment.java:81)
at android.arch.lifecycle.ViewModelStores.of(ViewModelStores.java:42)
at android.arch.lifecycle.ViewModelProviders.of(ViewModelProviders.java:88)
at com.mycompany.myapp.ui.splash.SplashActivity$viewModel$2.invoke(SplashActivity.kt:47)
at com.mycompany.myapp.ui.splash.SplashActivity$viewModel$2.invoke(SplashActivity.kt:40)
at kotlin.SynchronizedLazyImpl.getValue(Lazy.kt:130)
at com.mycompany.myapp.ui.splash.SplashActivity.getViewModel(SplashActivity.kt:0)
at com.mycompany.myapp.ui.splash.SplashActivity$onResume$1.run(SplashActivity.kt:62)
at android.os.Handler.handleCallback(Handler.java:815)
at android.os.Handler.dispatchMessage(Handler.java:104)
at android.os.Looper.loop(Looper.java:207)
at android.app.ActivityThread.main(ActivityThread.java:5805)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:789)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:679)
Here my code, but It's very weird because I'm not set on onDestroy()
class SplashActivity : AppCompatActivity(){
GoogleApiClient.OnConnectionFailedListener {
val context = this
val viewModel by lazy {
ViewModelProviders.of(this).get(ListModel::class.java)
}
override fun onResume() {
super.onResume()
Handler().postDelayed(object: Runnable{
override fun run() {
val testConnection = viewModel?.testConnectionLiveData()
viewModel?.testConnection()
testConnection?.observe(context, Observer<TestConnectionData> { tc ->
tc?.let {
if (tc.status == "FAILED") {
var builder: AlertDialog = AlertDialog.Builder(context).create()
builder.setTitle("Failed Connect To Server")
builder.setMessage("The app cannot reach on the server. Make sure your device connect the internet and try again!")
builder.setButton(AlertDialog.BUTTON_POSITIVE, "OK", object : DialogInterface.OnClickListener {
override fun onClick(dialog: DialogInterface?, which: Int) {
var i = Intent(context, LoginActivity::class.java)
startActivity(i)
}
})
builder.setIcon(android.R.drawable.ic_dialog_alert)
builder.setCancelable(false)
builder.setCanceledOnTouchOutside(false)
builder.show()
} else if(tc.status == "SUCCESS"){
var i = Intent(context, LoginActivity::class.java)
startActivity(i)
}
}
})
}
}, 5000)
}
#SuppressLint("MissingPermission")
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
window.setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
WindowManager.LayoutParams.FLAG_FULLSCREEN)
setContentView(R.layout.activity_splash)
}
}
I try to run again on Android studio, and everything is working normally.
I want to know why can happening and how solve it?

Looking into the Android source code, it checks if the support FragmentManager is destroyed when trying to get a ViewModel.
Calling
ViewModelProviders.of(this).get(ListModel::class.java)
will get to
private static HolderFragment findHolderFragment(FragmentManager manager) {
if (manager.isDestroyed()) {
throw new IllegalStateException("Can't access ViewModels from onDestroy");
}
Which will throw the exception if the FragmentManager is destroyed. Take care when the Runnable code executes with respect to the app lifecycle.
To solve this, you can:
check for getSupportFragmentManager().isDestroyed() before using the ViewModel
surround with try catch and ignore if does not affect your normal flow