I am trying to follow MVVM pattern in my Android app but getting error while creating an instance of ViewModel.
Error: Cannot create an instance of class DemoViewModel class.
Here is my code:
DemoFragment.kt:
class DemoFragment : Fragment(R.layout.fragment_demo) {
lateinit var mViewModel: DemoViewModel
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
mViewModel=ViewModelProvider(this).get(DemoViewModel::class.java)
mViewModel.getSomeData()
}
}
DemoViewModel.kt:
class DemoViewModel(val demoRepository: DemoRepository) : ViewModel() {
fun getSomeData() {
Log.d("DemoViewModel", "${demoRepository.getData()}")
}
}
DemoRepository.kt:
interface DemoRepository {
fun getData(): Boolean
}
class DemoImpl : DemoRepository {
override fun getData() = false
}
You need to use ViewModelFactory. Because there is "demoRepository" in your primary builder.
class DemoViewModelFactory constructor(private val repository:DemoImpl): ViewModelProvider.Factory {
override fun <T : ViewModel> create(modelClass: Class<T>): T {
return if (modelClass.isAssignableFrom(DemoViewModel::class.java!!)) {
DemoViewModel(this.repository) as T
} else {
throw IllegalArgumentException("ViewModel Not Found")
}
}
}
Usage
viewModel = ViewModelProvider(this, DemoViewModelFactory(repositoryObject)).get(DemoViewModel::class.java)
I would encourage you to use "by viewModels()" extension function to create viewModel instance easily. Note that you should add following dependency to use it:
implementation 'androidx.fragment:fragment-ktx:1.2.5'
Sample Fragment Implementation:
class DemoFragment : Fragment() {
// Use the 'by ViewModels()' Kotlin property delegate
// from the fragment-ktx artifact
private val model: DemoViewModel by viewModels()
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
model.selected.observe(viewLifecycleOwner, Observer<Item> { item ->
// Update the UI
})
}
}
Then you can inject an instance of your repository via constructor injection by Dagger or Hilt etc.
Related
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
}
}
i'm making an app and i want to separate my UI logic into multiple UI classes with BaseUi class being lifecycle aware. I'm using Kodein as my DI and i have an issue with fragment.viewLifecycleOwnerLiveData.observe not being called when instance of my ui class is being retrieved by Kodein.
Here is my Fragment class:
class ListFragment : Fragment(), DIAware {
override val di: DI by closestDI()
override val diTrigger: DITrigger = DITrigger()
private var binding: FragmentMoviesBinding? = null
private val fragmentBinding get() = binding
private val kodeinMoviesUi: MoviesUi by instance() //fragment does not observe viewLifecycleOwnerLiveData
private val moviesUi: MoviesUi = MoviesUi(this) //fragment now observe viewLifecycleOwnerLiveData
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
binding = FragmentMoviesBinding.inflate(inflater, container, false)
return binding?.root
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
diTrigger.trigger()
}
override fun onDestroyView() {
super.onDestroyView()
binding = null
}
}
BaseUi class:
abstract class BaseUi<F : Fragment>(private val fragment: F) : LifecycleObserver {
init {
fragment.viewLifecycleOwnerLiveData.observe(fragment, { subscribeToLifecycle() })
}
private fun subscribeToLifecycle() {
fragment.viewLifecycleOwner.lifecycle.addObserver(object : LifecycleObserver {
#OnLifecycleEvent(Lifecycle.Event.ON_CREATE)
fun onCreate() {
onViewCreated()
}
})
}
abstract fun onViewCreated()
}
And UiModule:
val uiModule = DI.Module("uiModule") {
bind<ListFragment>() with provider { ListFragment() }
bind<MoviesUi>() with provider { MoviesUi(instance()) }
}
Cross post from https://github.com/Kodein-Framework/Kodein-DI/issues/353
Here is your problem bind<ListFragment>() with provider { ListFragment() }.
You bound the ListFragment with a provider, meaning every time you ask to the container it will create an instance of ListFragment. So, when you inject MoviesUi with private val kodeinMoviesUi: MoviesUi by instance(), it gets another instance of ListFragment.
I suggest that you define the binding for MoviesUi as a factory, waiting to receive a ListFragment instance:
bind<MoviesUi>() with factory {fragment: ListFragment -> MoviesUi(fragment) }
then you can inject it in the ListFragment like:
private val kodeinMoviesUi: MoviesUi by instance(args = this)
I'm trying to send data from DialogFragment to Fragment using ViewModel but it seems both fragment and Dialog fragment are referencing different instances of ViewModel. so I can't access data . Is there any way I can fix this issue? thanks
Here is my Fragment
#AndroidEntryPoint
class FragmentToReceiveData:BaseFragment(R.layout.fragment_1){
private val viewModel: AddScheduleViewModel by viewModels()
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
Log.d(TAG, "onViewCreated: $viewModel") // will print ...MyViewModel#62274cc
viewModel.dataFromDialog.observe(viewLifecycleOwner){
//nothing happens
}
}
.
.
.
private fun openDialog(){
val action=FragmentToReceiveDataDirections.actionFragmentToReceiveDataToExampleDialog()
findNavController().navigate(action)
//exampleDialog.show(requireActivity().supportFragmentManager, "alarmDialog") //same issue
}
}
Here is ViewModel:
class MyViewModel #ViewModelInject constructor(){
var dataFromDialog=MutableLiveData<SomeClass>()
fun saveDataFromDialog(data:SomeClass){
dataFromDialog.value=data
}
}
Here is my DialogFragment
#AndroidEntryPoint
class ExampleDialog:DialogFragment() {
val viewModel:MyViewModel by viewModels()
override fun onCreateDialog(savedInstanceState: Bundle?): Dialog {
Log.d(TAG, "onCreateDialog: $viewModel") // will print ...MyViewModel#125436
.
.
.
viewMode.saveDataFromDialog(data)
}
}
P.S: I'm using single activity architecture, So I'm not sure if activityViewModels() is a good idea
in order to share ViewModel between fragments, you can use activityViewModels(). for instance,
class SharedViewModel : ViewModel() {
...
}
class MasterFragment : Fragment() {
// Use the 'by activityViewModels()' Kotlin property delegate
// from the fragment-ktx artifact
private val model: SharedViewModel by activityViewModels()
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
...
}
}
class DetailFragment : Fragment() {
// Use the 'by activityViewModels()' Kotlin property delegate
// from the fragment-ktx artifact
private val model: SharedViewModel by activityViewModels()
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
...
}
}
please read more in the android documentation here: https://developer.android.com/topic/libraries/architecture/viewmodel#sharing
I'm using Dagger 2 in clean architecture project, I have 2 fragments. These 2 fragments should be scoped together to share the same instances, but unfortunately, I got empty object in the second fragment.
Application Component
#ApplicationScope
#Component(modules = [ContextModule::class, RetrofitModule::class])
interface ApplicationComponent {
fun exposeRetrofit(): Retrofit
fun exposeContext(): Context
}
Data layer - Repository
class MoviesParsableImpl #Inject constructor(var moviesLocalResult: MoviesLocalResult): MoviesParsable {
private val TAG = javaClass.simpleName
private val fileUtils = FileUtils()
override fun parseMovies() {
Log.d(TAG,"current thread is ".plus(Thread.currentThread().name))
val gson = Gson()
val fileName = "movies.json"
val jsonAsString = MyApplication.appContext.assets.open(fileName).bufferedReader().use{
it.readText()
}
val listType: Type = object : TypeToken<MoviesLocalResult>() {}.type
moviesLocalResult = gson.fromJson(jsonAsString,listType)
Log.d(TAG,"result size ".plus(moviesLocalResult.movies?.size))
}
override fun getParsedMovies(): Results<MoviesLocalResult> {
return Results.Success(moviesLocalResult)
}
}
Repo Module
#Module
interface RepoModule {
#DataComponentScope
#Binds
fun bindsMoviesParsable(moviesParsableImpl: MoviesParsableImpl): MoviesParsable
}
MoviesLocalResultsModule(the result need its instance across different fragments)
#Module
class MoviesLocalResultModule {
#DataComponentScope
#Provides
fun provideMovieLocalResults(): MoviesLocalResult{
return MoviesLocalResult()
}
}
Use case
class AllMoviesUseCase #Inject constructor(private val moviesParsable: MoviesParsable){
fun parseMovies(){
moviesParsable.parseMovies()
}
fun getMovies(): Results<MoviesLocalResult> {
return moviesParsable.getParsedMovies()
}
}
Presentation Component
#PresentationScope
#Component(modules = [ViewModelFactoryModule::class],dependencies = [DataComponent::class])
interface PresentationComponent {
fun exposeViewModel(): ViewModelFactory
}
First ViewModel, where I got the result to be shared with the other fragment when needed
class AllMoviesViewModel #Inject constructor(private val useCase: AllMoviesUseCase):ViewModel() {
private val moviesMutableLiveData = MutableLiveData<Results<MoviesLocalResult>>()
init {
moviesMutableLiveData.postValue(Results.Loading())
}
fun parseJson(){
viewModelScope.launch(Dispatchers.Default){
useCase.parseMovies()
moviesMutableLiveData.postValue(useCase.getMovies())
}
}
fun readMovies(): LiveData<Results<MoviesLocalResult>> {
return moviesMutableLiveData
}
}
Second ViewModel where no need to request data again as it's expected to be scoped
class MovieDetailsViewModel #Inject constructor(private val useCase: AllMoviesUseCase): ViewModel() {
var readMovies = liveData(Dispatchers.IO){
emit(Results.Loading())
val result = useCase.getMovies()
emit(result)
}
}
First Fragment, where data should be requested:
class AllMoviesFragment : Fragment() {
private val TAG = javaClass.simpleName
private lateinit var viewModel: AllMoviesViewModel
private lateinit var adapter: AllMoviesAdapter
private lateinit var layoutManager: LinearLayoutManager
private var ascendingOrder = true
#Inject
lateinit var viewModelFactory: ViewModelFactory
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setHasOptionsMenu(true)
DaggerAllMoviesComponent.builder()
.presentationComponent(
DaggerPresentationComponent.builder()
.dataComponent(
DaggerDataComponent.builder()
.applicationComponent(MyApplication.applicationComponent).build()
)
.build()
).build()inject(this)
viewModel = ViewModelProvider(this, viewModelFactory).get(AllMoviesViewModel::class.java)
startMoviesParsing()
}
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
return inflater.inflate(R.layout.fragment_all_movies, container, false)
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
setupRecyclerView()
viewModel.readMovies().observe(viewLifecycleOwner, Observer {
if (it != null) {
when (it) {
is Loading -> {
showResults(false)
}
is Success -> {
showResults(true)
Log.d(TAG, "Data observed ".plus(it.data))
addMoviesList(it.data)
}
is Error -> {
moviesList.snack(getString(R.string.error_fetch_movies))
}
}
}
})
}
Second Fragment, where I expect to get the same instance request in First Fragment as they are scoped.
class MovieDetailsFragment: Fragment() {
val TAG = javaClass.simpleName
#Inject
lateinit var viewModelFactory: ViewModelFactory
lateinit var viewModel: MovieDetailsViewModel
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
val depend = DaggerAllMoviesComponent.builder()
.presentationComponent(
DaggerPresentationComponent.builder()
.dataComponent(
DaggerDataComponent.builder()
.applicationComponent(MyApplication.applicationComponent).build())
.build()
).build()
depend.inject(this)
viewModel = ViewModelProvider(this, viewModelFactory).get(MovieDetailsViewModel::class.java)
}
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
viewModel.readMovies.observe(this, Observer {
if (it!=null){
Log.d(TAG,"Movies returned successfully")
}
})
return super.onCreateView(inflater, container, savedInstanceState)
}
}
Scopes tell a component to cache the results of a binding. It has nothing to do with caching instances of any components. As such, you are always creating a new DataComponent, PresentationComponent, and AllMoviesComponent in your fragments' onCreate methods.
In order to reuse the same AllMoviesComponent instance, you need to store it somewhere. Where you store it can depend on your app architecture, but some options include MyApplication itself, the hosting Activity, or in your navigation graph somehow.
Even after fixing this, you can't guarantee that parseMovies has already been called. The Android system could kill your app at any time, including when MoviesDetailFragment is the current fragment. If that happens and the user navigates back to your app later, any active fragments will be recreated, and you'll still get null.
Trying to use Dagger with Kotlin on Android. And got the exception:
Caused by: kotlin.UninitializedPropertyAccessException: lateinit property presenter has not been initialized
at com.ad.eartquakekotlin.main.MainFragment.onViewCreated(MainFragment.kt:43)
at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManager.java:1471)
at androidx.fragment.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManager.java:1784)
at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManager.java:1852)
at androidx.fragment.app.BackStackRecord.executeOps(BackStackRecord.java:802)
at ...
The app is special for testing. I get earthquakes and show them on a device screen.
All I want is
1. Inject the presenter in my Fragment (View)
2. Inject the api in my presenter
There is the structure of my project:
There are two modules and components there, as you can see:
#Module
class ApplicationModule(private val application: Application) {
#Provides
#Singleton
fun provideApplication():Application = application
}
#Module
class MainModule (private val view: MainContract.View) {
#Provides
fun provideView(): MainContract.View {
return view
}
#Provides
fun providePresenter(): MainContract.Presenter {
return MainPresenter(view)
}
}
And components:
#Component(modules = [ApplicationModule::class])
interface ApplicationComponent {
fun inject(application: Application)
fun plus (mainModule: MainModule) : MainComponent
}
and
#Subcomponent(modules = [MainModule::class])
interface MainComponent {
fun inject (view : MainContract.View)
}
There is a contract:
interface MainContract {
interface View {
fun showLoading()
fun hideLoading()
fun showMessage(message: String)
fun showData(data: EarthquakeRootObject)
}
interface Presenter {
fun onDestroy()
fun loadData()
}
}
Application class:
class MainApp: Application() {
companion object {
lateinit var graph: ApplicationComponent
}
override fun onCreate() {
super.onCreate()
buildGraph()
}
private fun buildGraph() {
graph = DaggerApplicationComponent
.builder()
.applicationModule(ApplicationModule(this))
.build()
}
}
Fragment (where I want to use Injection)
class MainFragment : Fragment(), MainContract.View {
private lateinit var earthquakesAdapter: EarthquakeRecyclerViewAdapter
private lateinit var earthquakes: EarthquakeRootObject
#Inject lateinit var presenter: MainContract.Presenter
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?): View? {
return container?.inflate(R.layout.fragment_main)
}
override fun onAttach(context: Context?) {
super.onAttach(context)
MainApp.graph.plus(MainModule(this)).inject(this)
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
earthquakesRecyclerView.layoutManager = LinearLayoutManager(context)
earthquakesRecyclerView.setHasFixedSize(true)
presenter.loadData()
}
And my presenter
class MainPresenter (var view: MainContract.View?) : MainContract.Presenter {
private var disposable: Disposable? = null
#Inject lateinit var api : EarthquakeApi
override fun onDestroy() {
disposable?.dispose()
view = null
}
override fun loadData() {
view?.showLoading()
disposable = api.getEarthquakes()
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(
{
response ->
view?.showData(response)
view?.hideLoading()
},
{
throwable ->
view?.showMessage(throwable.message ?: "Ошибка")
view?.hideLoading()
}
)
}
What do I do wrong?
You need to replace
fun inject (view : MainContract.View)
with
fun inject(target : MainFragment)