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Android LiveData was observed in three fragments, but only one is actually observing and upadate UI. Other two are not observing

I have tried this problem all days long and still cannot be resolved.
I am writing an app which has three fragments, connected by Navigation Component (with only one activity).
Fragment A
Fragment B
Fragment C
And I observed one LiveData variable from ViewModel in these three fragments.
But only Fragment B is responding. The other two are not.
I have read almost all similar problems from this stack over flow. But still can't see the answer.
Please suggest me.
I have tried removing the observer from FragmentB (which is ok with observing Live Data). But the other two is not still observing)
Here is my code:
Fragment B: (Observe Working)
class ServerFragment : Fragment() {
private lateinit var binding: ServerLayoutBinding
private val vm: DataModel by viewModels()
private lateinit var devices_observer: Observer<MutableList<ClientSocket>>
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
binding = ServerLayoutBinding.inflate(inflater, container, false)
return binding.root
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
var client_list_adapter = ClientListAdapter(layoutInflater)
binding.clientListRcv.apply {
layoutManager = LinearLayoutManager(this.context)
addItemDecoration(
DividerItemDecoration(
this.context,
DividerItemDecoration.VERTICAL
)
)
adapter = client_list_adapter
}
client_list_adapter.submitList(vm.clientDevices.value?.toList())
vm.clientDevices.observe(viewLifecycleOwner, Observer {
client_list_adapter.submitList(vm.clientDevices.value?.toList())} )
}
}
Fragment C: (Observe Not Working)
class FileListFragment: Fragment() {
private val vm: DataModel by viewModels()
private lateinit var binding: FileListBinding
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
binding=FileListBinding.inflate(inflater, container, false)
return binding.root
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
//Here I am populating my recycler view with ViewModel data
//And ViewModel live dat is obeserving here and
vm.clientDevices.observe(viewLifecycleOwner, Observer{
///Here UI updating work will be done. But did'not responded. Here is the problem point I think.
Toast.makeText(context, "OKKK", Toast.LENGTH_SHORT).show()
})
}
}

How to run code just one time in Fragment on Android

In my application I have some fragments and for show this fragments I want use NavigationComponent.
I have one problem. When click on BottomNavigationItems and change fragments, run again fragment code!
I want just run codes just for first time!
My codes (for one of fragments) :
#AndroidEntryPoint
class HomeNewFragment : Fragment(), HomeContracts.View {
//Binding
private lateinit var binding: FragmentHomeNewBinding
#Inject
lateinit var presenter: HomePresenter
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View {
binding = FragmentHomeNewBinding.inflate(layoutInflater)
return binding.root
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
//InitViews
binding.apply {
//Call apis
presenter.callApi()
}
}
}
For example when click on items, every time call this code : presenter.callApi()
Or when go to DetailFragment and when click on back, again call presenter.callApi()
How can I fix it?

You should replace your presenter.callApi() with fun onFragmentCreated triggered in your Presenter(ViewModel).
All you need is a boolean var to check its first time or not cause your Presenter(ViewModel) attatched to the activity, not the fragment so it can store your state.
Presenter {
fun onFragmentCreated() {
if(firstTime) callApi()

LiveData is not observing on child viewpager fragments having a shared viewmodel

LiveData is not observing on child viewpager fragments where the child fragments have one shared viewmodel to access data.
Here FragmentA and FragmentB are part of a viewpager and both of them are sharing one viemodel SharedViewModel.
public class SharedViewModel extends AndroidViewModel { //in Java
private final MutableLiveData<Data> mLiveData = new MutableLiveData<>();
public LiveData<Data> getLiveData() {
return mLiveData;
}
//for updating data through LiveData, using post as and when I get the response from DataSource as shown below.
mLiveData.postValue(response); //getting the response on debugging
}
class FragmentA : Fragment() { //in Kotlin
override fun onCreate(#Nullable savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
mViewModel = ViewModelProvider(this).get(SharedViewModel::class.java)
}
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View {
....
mViewModel.liveData.observe(viewLifecycleOwner, {
//no call coming in this block so unable to update view
})
}
}
class FragmentB : Fragment() { //in Kotlin
override fun onCreate(#Nullable savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
mViewModel = ViewModelProvider(this).get(SharedViewModel::class.java)
}
}
Need some help as to why the live data is not able to observe the changes.
Thanks in advance.

Your ViewModel is not shared. you have named it as sharedViewmodel but the way you are getting an instance of it by passing a Unique Owner it will also be a unique instance.
the correct way of sharing view model is
class SharedViewModel : ViewModel() {
private val myLiveData = MutableLiveData<Data>()
fun getMyLiveDta():LiveData {
return myLiveData
}
}
Now in the first fragment
class MasterFragment : Fragment() {
private lateinit var itemSelector: Selector
// Get instance of viewmodel in fragment like this
private val model: SharedViewModel by activityViewModels()
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
}
}
And in the second fragment like this
class DetailFragment : Fragment() {
private val model: SharedViewModel by activityViewModels()
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
model.selected.observe(viewLifecycleOwner, Observer<Item> { item ->
// Update the UI
})
}
}

How to implement databinding with Reflection in BaseFragment()

I'm trying to implement a BaseFragment in which I will pass the layout resource on it and it should outputs the binding to work in the fragment itself instead of need to do it everytime the fragment is extended.
For example I have this BaseFragment
open class BaseFragment(#LayoutRes contentLayoutId : Int = 0) : Fragment(contentLayoutId) {
private lateinit var onInteractionListener: OnFragmentInteractionListener
val toolbar : Toolbar?
get() {
return if(activity is BaseActivity)
(activity as BaseActivity).toolbar
else
null
}
override fun onAttach(context: Context) {
super.onAttach(context)
setOnInteractionListener(context)
}
...
In which I use like this
class A(): BaseFragment(R.layout.myFragment) { ... }
Now, if I use this I will need to do the definition of the binding class again in my onCreateView
class A(): BaseFragment(R.layout.myFragment) {
private lateinit var binding: MyFragmentBinding
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?): View? {
binding = DataBindingUtil.inflate(inflater, R.layout.myFragment, container, false)
return binding.root
}
override fun onDestroy(){
binding = null
}
}
What I want to implement is that since I'm passwing the layout to my BaseFragment, I want my BaseFragment to handle the creation of the binding and just return me the binding in the fragment which I use to extend BaseFragment
What I want to have is something like this
class A(): BaseFragment(R.layout.myFragment) {
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
binding.myTextView = ""
}
}
So my question is, how I can implement inside BaseFragment the onDestroy() and the onCreateView to always create a binding for me from the layout I'm passing in ?
I heard that I should use reflection but I'm not that sure on how to accomplish it

I didn't hear about the possibility to get the databinding just from a layout, but even if it's possible, I don't think that is the recommended way, because of two reasons:
Reflection is slow
It makes things more complicated than they are.
Instead of making magic with Reflection, you could do something like this:
abstract class BaseFragment<out VB: ViewDataBinding>(
private val layout: Int,
// Other Dependencies if wanted
) : Fragment() {
abstract val viewModel: ViewModel
// other variables that all fragments need
// This does not cause any memory leak, because you are not storing the binding property.
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View? = DataBindingUtil.inflate<VB>(inflater, layout, container, false).apply {
lifecycleOwner = viewLifecycleOwner
setVariable(BR.viewModel, viewModel)
}.root
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
// Do some basic work here that all fragments need
// like a progressbar that all fragments share, or a button, toolbar etc.
}
And then, when you still need the bindingProperty, I would suggest the following library (it handles all the onDestoryView stuff etc):
implementation 'com.kirich1409.viewbindingpropertydelegate:viewbindingpropertydelegate:1.2.2'
You can then use this like:
class YourFragment(yourLayout: Int) : BaseFragment<YourBindingClass>() {
private val yourBinding: YourBindingClass by viewBinding()
override val viewModel: YourViewModel by viewModels()
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
// do binding stuff
}
}
Let me know if this worked for you.
Cheers

how to create new instance of viewModel in koin every time

Am Using Koin as Dependency injection pattern in my project, I need to create new instances whenever i load fragment/activity, now am using the following pattern, Any solution for that it might save lots of time.
private val homeViewModel: HomeViewModel by viewModel()

The question is why you want new instances everytime? The whole concept of ViewModel is to retain the same instance and data. viewModel {} creates new instance everytime you inject it unless it is not shared.
Don't know why it is not working for you, but I think you can use factory{} instead of viewModel{}.
factory{
// this is because you need new instance everytime.
HomeViewModel()
}

Define ViewModel as an abstract in BaseFragment class and set value when you extend your BaseFragment.
abstract class BaseFragment<Binding : ViewDataBinding, ViewModel : BaseViewModel> : Fragment(){
protected var bindingObject: Binding? = null
protected abstract val mViewModel: ViewModel
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
bindingObject = DataBindingUtil.inflate(inflater, getLayoutResId(), container, false)
return bindingObject?.root
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
performDataBinding()
}
#LayoutRes
abstract fun getLayoutResId(): Int
private fun performDataBinding() {
bindingObject?.setLifecycleOwner(this)
bindingObject?.setVariable(BR.viewModel, mViewModel)
bindingObject?.executePendingBindings()
}
}
And in your fragment
class FragmentNew : BaseFragment<FragmentNewBinding, FragmentNewVM>() {
// Here is the your viewmodel imlementation. Thus when you create fragment it's by default override method
override val mViewModel: FragmentNewVM by viewModel()
override fun getLayoutResId(): Int = [fragment layout id like "R.layout.fragment_new"]
}

You are going to want to forego using by viewmodel and instantiate the class directly. You can get global (scoped) variables through getKoin().get().
private val viewModel = HomeViewModel(getKoin().get())