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How to use same viewModel method inside multiple fragment?

I want use one viewModel and observe object from one method. But I dont want write this observe method in all fragment. Only write in one place and use other fragments. I think I need fragment extension but can't get it how do this. I need help.
This viewModel that I want use.
SharedViewModel.kt
class SharedViewModel #Inject constructor(private val notificationServiceRepo: NotificationServiceRepo) : ViewModel() {
private val _helpNotification = SingleLiveEvent<NetworkResult<BaseResponse<Any>>>()
val helpNotification get() = _helpNotification
fun postHelpNotification(helpNotificationRequest: HelpNotificationRequest) = viewModelScope.launch (
Dispatchers.IO){
_helpNotification.postValue(NetworkResult.Loading)
_helpNotification.postValue(notificationServiceRepo.postNotificationHelp(helpNotificationRequest))
}
}
this is call method and observe function:
MainFragment.kt
viewModel.postHelpNotification(HelpNotificationRequest(0))
viewModel.helpNotification.observe(viewLifecycleOwner) {
it?.onLoading {}
it?.onSuccess { result->
result?.let {
InfoDialogWithOneText(
InfoDialogType.GOT_HELP_ASKING_FROM_STAFF
).show(childFragmentManager, InfoDialog.TAG)
}
}
it?.onError { error ->
InfoDialogWithOneText(
InfoDialogType.GOT_HELP_ASKING_FROM_STAFF
).show(childFragmentManager, InfoDialog.TAG)
}
}
}
Tried use sharedViewModel but I will have to write observe method for all.
Tried to baseViewModel but it get error hilt view model and also it will be same like shared view model.

For the abstract part, you want it need to cover everything - from having a view model that provides the observable event and handling it. I had to change some types because you did not provide them but it should not be too difficult to apply this to your case.
abstract class HelpNotificationFragment : Fragment() {
internal abstract val viewModel: HelpNotificationViewModel
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
viewModel.helpNotification.observe(viewLifecycleOwner) { result ->
println(result)
}
}
}
abstract class HelpNotificationViewModel : ViewModel() {
private val _helpNotification = SingleLiveEvent<Result<Any>>()
// Specify the immutable type otherwise you would expose it as mutable
val helpNotification: LiveData<Result<Any>>
get() = _helpNotification
fun postHelpNotification(helpNotificationRequest: Result<Any>) {
viewModelScope.launch(Dispatchers.IO) {
_helpNotification.postValue(helpNotificationRequest)
}
}
}
And this is how you would implement the fragments that would use it - the overriding the view model will take care of forcing you to use view model with proper parent:
#HiltViewModel
class MainViewModel #Inject constructor(): HelpNotificationViewModel()
#AndroidEntryPoint
class MainFragment : HelpNotificationFragment() {
override val viewModel: MainViewModel by viewModels()
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
val view = inflater.inflate(R.layout.fragment_main, container, false)
view.findViewById<Button>(R.id.button).setOnClickListener {
viewModel.postHelpNotification(Result.success("Yay!"))
}
return view
}
}

How to pass data that changes real-time from activity to fragment?

I am currently reading data from a Bluetooth Sensor, hence the data changes in real-time and continuously changes. I have stored the data in a variable: liveData:ByteArray
Now I am trying to send liveData from MainActivity to Sensordisplayfragment.
UPDATE
Based on #CTD's comment, this is what I have tried, unfortunately I do not have much knowledge on viewModel, and online research is just confusing as there seems to be many methods to implement a viewModel.
In my MainActivity class where variable liveData is stored:
val model:MyViewModel by viewModels()
private fun processLiveData(liveData : ByteArray){
livedata = liveData
model.uploadData(livedata)
}
In MyViewModel.class where the viewModel is at:
class MyViewModel: ViewModel() {
private val realtimedata = MutableLiveData<ByteArray>()
fun uploadData(data:ByteArray){
realtimedata.value = data
}
fun loadData():LiveData<ByteArray>{
return realtimedata
}
}
Finally, in my Sensordisplay fragment where I am fetching the data:
val model:MyViewModel by viewModels()
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
model.loadData().observe(viewLifecycleOwner,Observer<ByteArray>{
passandprocessLiveData(it)
})
return inflater.inflate(R.layout.sensordisplay, container, false)
}
override fun onResume(){
activity?.requestedOrientation = ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE
model.loadData().observe(viewLifecycleOwner,Observer<ByteArray>{
passandprocessLiveData(it)
})
super.onResume()
}
fun passandprocessLiveData(data:Bytearray){
//extract information from data and make
//cardviews move in realtime according to the extracted data
}
Unfortunately,nothing is getting transferred and my cardviews are not moving. I can guarantee there is no error in the moving of the cardview codes. Anyone able to advice on what I can add? Apparently there is an init() function that I need to use.

class MyViewModel : ViewModel() {
private val realtimedata = MutableLiveData<ByteArray>()
val sensorData: LiveData<ByteArray> = realtimedata
fun update(data: ByteArray){
realtimedata.value = data
}
}
class MainActivity: Activity() {
private val viewModel: MyViewModel by viewModels()
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
bluetoothSensorCallBack { data ->
// Update the realtimedata
viewModel.update(data)
}
}
}
class SensordisplayFragment : Fragment() {
// Use the 'by activityViewModels()' Kotlin property delegate
// from the fragment-ktx artifact
private val model: MyViewModel by activityViewModels()
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
model.sensorData.observe(viewLifecycleOwner, Observer<ByteArray> { data ->
// Update the UI
})
}
}

LiveData binding observer being registered multiple times when changing device orientation even when using viewLifeCycleOwner

I have a view model that is data binded to a fragment. The view model is shared with the main activity.
I've button is binded to the view as follows:
<Button
android:id="#+id/startStopBtn"
android:text="#{dashboardViewModel.startStopText == null ? #string/startBtn : dashboardViewModel.startStopText}"
android:onClick = "#{() -> dashboardViewModel.onStartStopButton(context)}"
android:layout_width="83dp"
android:layout_height="84dp"
android:layout_gravity="center_horizontal|center_vertical"
android:backgroundTint="#{dashboardViewModel.isRecStarted == false ? #color/startYellow : #color/stopRed}"
tools:backgroundTint="#color/startYellow"
android:duplicateParentState="false"
tools:text="START"
android:textColor="#FFFFFF" />
What I expect to happen is that every time I press the button the function onStartStopButton(context) runs. This works fine as long as I don't rotate the device. When I rotate the device the function is run twice, if I rotate again the function is run 3 times and so on. This is not a problem if I go to another fragment and then back to the dashboard fragment. It looks like the live data observer is getting registered every time I rotate my screen, but not every time I detach and reattach the fragment.
This is true for all the elements in that fragment, whether they are data binded or I manually observe them.
Fragment code:
class DashboardFragment : Fragment() {
private var _binding: FragmentDashboardBinding? = null
private val binding get() = _binding!!
private val dashboardViewModel: DashboardViewModel by activityViewModels()
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
_binding = FragmentDashboardBinding.inflate(inflater, container, false)
val root: View = binding.root
binding.dashboardViewModel = dashboardViewModel
binding.lifecycleOwner = viewLifecycleOwner
dashboardViewModel.bleSwitchState.observe(viewLifecycleOwner, Observer { switchState -> handleBleSwitch(switchState) })
dashboardViewModel.yLims.observe(viewLifecycleOwner, Observer { yLims ->
updatePlotWithNewData(yLims.first, yLims.second)
})
Timber.i("Dahsboard on create: DashboardViewModel in fragment: $dashboardViewModel")
return root
}
}
The view model:
class DashboardViewModel : ViewModel() {
//region live data
private var _isRecStarted = MutableLiveData<Boolean>()
val isRecStarted: LiveData<Boolean> get() = _isRecStarted
//private var _bleSwitchState = MutableLiveData<Boolean>()
val bleSwitchState = MutableLiveData<Boolean>()
private var _startStopText = MutableLiveData<String>()
val startStopText: LiveData<String> get() = _startStopText
private var _yLims = MutableLiveData<Pair<kotlin.Float,kotlin.Float>>()
val yLims: LiveData<Pair<kotlin.Float,kotlin.Float>> get() = _yLims
//endregion
init {
Timber.d("DashboardViewModel created!")
bleSwitchState.value = true
}
//region start stop button
fun onStartStopButton(context: Context){
Timber.i("Start stop button pressed, recording data size: ${recordingRawData.size}, is started: ${isRecStarted.value}")
isRecStarted.value?.let{ isRecStarted ->
if (!isRecStarted){ // starting recording
_isRecStarted.postValue(true)
_startStopText.postValue(context.getString(R.string.stopBtn))
startDurationTimer()
}else{ // stopping recording
_isRecStarted.postValue(false)
_startStopText.postValue(context.getString(R.string.startBtn))
stopDurationTimer()
}
} ?: run{
Timber.e("Error! Is rec started is not there for some reason")
}
}
}
The view model is created the first time from the MainActivity as follows:
class MainActivity : AppCompatActivity() {
private val dashboardViewModel: DashboardViewModel by viewModels()
override fun onCreate(savedInstanceState: Bundle?) {
Timber.i("DashboardViewModel in main activity: $dashboardViewModel")
}
}
Edit explaining why the MainActivity is tided to the ViewModel:
The reason why the ViewModel is linked to the main activity is that the main activity handles some Bluetooth stuff for a stream of data, when a new sample arrives then the logic to handle it and update the UI of the dashboard fragment is on the DashboardViewModel. The data still needs to be handled even if the dashboard fragment is not there.
So I need to pass the new sample to the DashboardViewModel from the main activity as that is where I receive it. Any suggestions to make this work?

As you know, when you instantiate the ViewModel of a Fragment with activityViewModels, it means that the ViewModel will follow the lifecycle of the Activity containing that Fragment. Specifically here is MainActivity.
So what does ViewModel tied to Activity lifecycle mean in your case?
When you return to the Fragment, normally LiveData (with ViewModel attached to Fragment lifcycler) will trigger again.
But when that ViewModel is attached to the Activity's lifecycle, the LiveData will not be triggered when returning to the Fragment.
That leads to when you return to the Fragment, your LiveData doesn't trigger again.
And that LiveData only triggers according to the life cycle of the activity. That is, when you rotate the screen, the Activity re-initializes, now your LiveData is triggered.
EDIT:
Here, I will give you one way. Maybe my code below doesn't work completely for your case, but I think it will help you in how to control LiveData and ViewModel when you bind ViewModel to Activity.
First, I recommend that each Fragment should have its own ViewModel and it should not depend on any other Fragment or Activity. Here you should rename the DashboardViewModel initialized by activityViewModels() as ShareViewModel or whatever you feel it is related to this being the ShareViewModel between your Activity and Fragment.
class DashboardFragment : Fragment() {
// Change this `DashboardViewModel` to another class name. Could be `ShareViewModel`.
private val shareViewModel: ShareViewModel by activityViewModels()
// This is the ViewModel attached to the DashboardFragment lifecycle.
private val viewModel: DashboardViewModel by viewModels()
private lateinit var _binding: FragmentDashboardBinding? = null
private val binding get() = _binding!!
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
_binding = FragmentDashboardBinding.inflate(inflater, container, false)
binding.dashboardViewModel = viewModel
binding.lifecycleOwner = viewLifecycleOwner
return binding.root
}
override fun onDestroyView() {
_binding = null
super.onDestroyView()
}
}
Next, when there is data triggered by the ShareViewModel's LiveData, you will set the value for the LiveData in the ViewModel associated with your Fragment. As follows:
DashboardViewModel.kt
class DashboardViewModel: ViewModel() {
private val _blueToothSwitchState = MutableLiveData<YourType>()
val blueToothSwitchState: LiveData<YourType> = _blueToothSwitchState
private val _yLims = MutableLiveData<Pair<YourType, YourType>>()
val yLims: LiveData<Pair<YourType, YourType>> = _blueToothSwitchState
fun setBlueToothSwitchState(data: YourType) {
_blueToothSwitchState.value = data
}
fun setYLims(data: Pair<YourType, YourType>) {
_yLims.value = data
}
}
DashboardFragment.kt
class DashboardFragment : Fragment() {
...
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
shareViewModel.run {
bleSwitchState.observe(viewLifeCycleOwner) {
viewModel.setBlueToothSwitchState(it)
}
yLims.observe(viewLifeCycleOwner) {
viewModel.setYLims(it)
}
}
viewModel.run {
// Here, LiveData fires observe according to the life cycle of `DashboardFragment`.
// So when you go back to `DashboardFragment`, the LiveData is re-triggered and you still get the observation of that LiveData.
blueToothSwitchState.observe(viewLifeCycleOwner, ::handleBleSwitch)
yLims.observe(viewLifeCycleOwner) {
updatePlotWithNewData(it.first, it.second)
}
}
}
...
}
Edit 2:
In case you rotate the device, the Activity and Fragment will be re-initialized. At that time, LiveData will fire observe. To prevent that, use Event. It will keep your LiveData from observing the value until you set the value again for LiveData.
First, let's create a class Event.
open class Event<out T>(private val content: T) {
var hasBeenHandled = false
private set
fun getContentIfNotHandled(): T? = if (hasBeenHandled) {
null
} else {
hasBeenHandled = true
content
}
fun peekContent(): T = content
}
Next, modify the return type of the LiveData that you want to trigger once.
ShareViewModel.kt
class ShareViewModel: ViewModel() {
private val _test = MutableLiveData<Event<YourType>>()
val test: LiveData<Event<YourType>> = _test
fun setTest(value: YourType) {
_test.value = Event(value)
}
}
Add this extension to easily get LiveData's observations.
LiveDataExt.kt
fun <T> LiveData<Event<T>>.eventObserve(owner: LifecycleOwner, observer: (t: T) -> Unit) {
this.observe(owner) { it?.getContentIfNotHandled()?.let(observer) }
}
Finally in the view, you get the data observed by LiveDatat.
class DashboardFragment : Fragment() {
...
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
shareViewModel.test.eventObserve(viewLifeCycleOwner) {
Timber.d("This is test")
}
}
...
}
Note: When using LiveData with Event, make sure that LiveData is not reset when rotating the device. If LiveData is set to value again, LiveData will still trigger even if you use Event.

Fragment. getViewLifeCycleOwner doesn't prevent multiple calls of LiveData Observer

I use Clean Architecture, LiveData, Navigation component & Bottom Navigation view.
I am creating a simple application with three tabs. By default, the First tab Fragment loads user data using some API. When i go to another tabs and then return to the First tab Fragment, i see, that observe return a new data!
I need observe not to return data again when I switch back to the first tab! what am I doing wrong? Could you help me please?
P.s. For navigation i use sample from navigation-advanced-sample and after switching tabs onDestroy is not called.
First solution in the article Observe LiveData from ViewModel in Fragment said:
One proper solution is to use getViewLifeCycleOwner() as LifeCycleOwer while observing LiveData inside onActivityCreated as follows.
I use following code, but it's not work for me:
override fun onActivityCreated(savedInstanceState: Bundle?) {
super.onActivityCreated(savedInstanceState)
Timber.d("onActivityCreated")
viewModel.getProfileLive().observe(viewLifecycleOwner, observer)
}
Second solution in the article Architecture Components pitfalls — Part 1 recommends using Resetting an existing observer and Manually unsubscribing the observer in onDestroyView(). But it doesn't work for me either...
ProfileFragment.kt
class ProfileFragment : DaggerFragment() {
#Inject
lateinit var viewModel: ProfileFragmentViewModel
private val observer = Observer<Resource<Profile>> {
when (it.status) {
Resource.Status.LOADING -> {
Timber.i("Loading...")
}
Resource.Status.SUCCESS -> {
Timber.i("Success: %s", it.data)
}
Resource.Status.ERROR -> {
Timber.i("Error: %s", it.message)
}
}
};
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
Timber.d("onCreate")
}
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
Timber.d("onCreateView")
return inflater.inflate(R.layout.fragment_profile, container, false)
}
fun <T> LiveData<T>.reObserve(owner: LifecycleOwner, observer: Observer<T>) {
removeObserver(observer)
observe(owner, observer)
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
Timber.d("onViewCreated")
viewModel.getProfileLive().observe(viewLifecycleOwner, observer)
// viewModel.getProfileLive().reObserve(viewLifecycleOwner, observer)
}
override fun onActivityCreated(savedInstanceState: Bundle?) {
super.onActivityCreated(savedInstanceState)
Timber.d("onActivityCreated")
}
override fun onDestroyView() {
super.onDestroyView()
Timber.d("onDestroyView")
// viewModel.getProfileLive().removeObserver(observer)
}
override fun onDestroy() {
super.onDestroy()
Timber.d("onDestroy")
}
override fun onDetach() {
super.onDetach()
Timber.d("onDetach")
}
}
ProfileFragmentViewModel.kt
class ProfileFragmentViewModel #Inject constructor(
private val profileUseCase: ProfileUseCase
) : ViewModel() {
init {
Timber.d("Init profile VM")
}
fun getProfileLive() = profileUseCase.getProfile()
}
ProfileUseCase
class ProfileUseCase #Inject constructor(
private val profileRepository: ProfileRepository
) {
fun getProfile(): LiveData<Resource<Profile>> {
return profileRepository.getProfile()
}
}
ProfileRepository.kt.
class ProfileRepository #Inject constructor(
private val loginUserDao: LoginUserDao,
private val profileDao: ProfileDao,
) {
fun getProfile(): LiveData<Resource<Profile>> =
liveData(Dispatchers.IO)
{
emit(Resource.loading(data = null))
val profile = profileDao.getProfile()
// Emit Success result...
}
}

It's because of how Fragment Lifecycle works. When you move to and fro from a fragment onViewCreated() is called again. In onViewCreated you're calling viewModel.getProfileLive() which returns the livedata upto from the repository and observe to it.
Since onViewCreated() gets called everytime when you move back to the Fragment so is your call to viewModel.getProfileLive() and in turn the repository gets called again which again triggers the observe method in your Fragment.
In order to solve this problem,
create a LiveData variable in your ViewModel, set it to the returned Live Data from Repository.
In the Fragment observe to the LiveData variable of your ViewModel not the one returned from Repository.
That way, your observe method will get triggered on very first time and only when value of your data from repository changes.

Fun with flows, getting null when converting to live data

I am trying out flows and trying to see how they can be converted to mvvm with android view models. Here is what I tried first to test it out :
class HomeViewModel : ViewModel() {
private lateinit var glucoseFlow: LiveData<Int>
var _glucoseFlow = MutableLiveData<Int>()
fun getGlucoseFlow() {
glucoseFlow = flowOf(1,2).asLiveData()
_glucoseFlow.value = glucoseFlow.value
}
}
class HomeFragment : Fragment() {
private lateinit var viewModel: HomeViewModel
override fun onCreateView (
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
return inflater.inflate(R.layout.home_fragment, container, false)
}
override fun onActivityCreated(savedInstanceState: Bundle?) {
super.onActivityCreated(savedInstanceState)
viewModel = ViewModelProviders.of(this).get(HomeViewModel::class.java)
viewModel._glucoseFlow.observe(this, Observer {
handleUpdate(it)
})
viewModel.getGlucoseFlow()
}
private fun handleUpdate(reading : Int) {
glucose_reading.text = reading.toString()
}
}
I get a null for the reading number however any ideas ?

This happens because you are trying to assign glucoseFlow.value to _glucoseFlow.value directly, I guess you should use a MediatorLiveData<Int>, however this is not my final suggestion.
You can solve it if you collect flow items and then assign them to your private variable.
// For private variables, prefer use underscore prefix, as well MutableLiveData for assignable values.
private val _glucoseFlow = MutableLiveData<Int>()
// For public variables, prefer use LiveData just to read values.
val glucoseFlow: LiveData<Int> get() = _glucoseFlow
fun getGlucoseFlow() {
viewModelScope.launch {
flowOf(1, 2)
.collect {
_glucoseFlow.value = it
}
}
}
Having the before implementation over the HomeViewModel, start to observe your public glucoseFlow from HomeFragment and you will be able to receive non-null sequence values (1 and then 2).

If you are using databinding, do not forget specify the fragment view as the lifecycle owner of the binding so that the binding can observe LiveData updates.
class HomeFragment : Fragment() {
...
binding.lifecycleOwner = viewLifecycleOwner
}