Android Room ViewModel initialization in fragment crashes app - android

The situation is pretty straightforward. I have a simple android app with 4 fragments displayed through a bottom navigation bar, and a central Room database. Each fragment should be able to perform CRUD operations on the DB through a viewmodel (details are probably irrelevant but I'll show this as well to be sure):
class ViewModel(application: Application): AndroidViewModel(application) {
val readAllIngredients: LiveData<List<Ingredient>>
val readAllRecipes: LiveData<List<Recipe>>
private val ingredientRepository: IngredientRepository
private val recipeRepository: RecipeRepository
init {
val ingredientDAO = ShoppingAppDatabase.getDatabase(application).ingredientDAO()
val recipeDAO = ShoppingAppDatabase.getDatabase(application).recipeDAO()
ingredientRepository = IngredientRepository(ingredientDAO)
recipeRepository = RecipeRepository(recipeDAO)
readAllIngredients = ingredientRepository.allIngredients
readAllRecipes = recipeRepository.allRecipes
}
fun addIngredient(ingredient: Ingredient) {
viewModelScope.launch(Dispatchers.IO) {
ingredientRepository.put(ingredient)
}
}
fun deleteIngredient(ingredient: Ingredient) {
viewModelScope.launch(Dispatchers.IO) {
ingredientRepository.delete(ingredient)
}
}
fun addRecipe(recipe: Recipe) {
viewModelScope.launch(Dispatchers.IO) {
recipeRepository.put(recipe)
}
}
fun updateRecipe(recipe: Recipe) {
viewModelScope.launch(Dispatchers.IO) {
recipeRepository.update(recipe)
}
}
fun updateIngredient(ingredient: Ingredient) {
viewModelScope.launch(Dispatchers.IO) {
ingredientRepository.update(ingredient)
}
}
}
I'm initializing a viewmodel in each fragment, but with limited success. Here's a fragment for which everything works fine:
class InventoryFragment() : Fragment() {
private var listAdapter = IngredientAdapter()
private lateinit var viewModel : ViewModel
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
}
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_inventory, container, false)
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
listAdapter = IngredientAdapter()
recycler_view.apply {
layoutManager = LinearLayoutManager(activity)
adapter = listAdapter
}
viewModel = ViewModelProvider(this).get(ViewModel::class.java)
viewModel.readAllIngredients.observe(viewLifecycleOwner, Observer { ingredient -> listAdapter.setData(ingredient) })
add_button.setOnClickListener{
val errorMessages = validateInput()
if(errorMessages.isNotEmpty()) {
displayToast(activity, errorMessages)
}
else {
viewModel.addIngredient(Ingredient(
edit_name.text.toString(),
edit_qty.text.toString().toFloat(),
edit_um.text.toString()
))
listAdapter.notifyDataSetChanged()
displayToast(activity, "Ingredient added")
hideKeyboard(activity, requireView().windowToken)
}
clearInput()
}
}
}
I'm initializing it in the onViewCreated callback and yeah, it works fine. Doing the same thing in a different fragment yields.. different results for some reason.
class BrowseFragment() : Fragment() {
private lateinit var viewModel: ViewModel
var recipeAdapter = RecipeAdapter()
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
}
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
return inflater.inflate(R.layout.fragment_browse, container, false)
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
viewModel = ViewModelProvider(this).get(ViewModel::class.java)
viewModel.readAllRecipes.observe(viewLifecycleOwner, Observer { recipe -> recipeAdapter.setData(recipe) })
submit_button.setOnClickListener{
var submitFragment = SubmitFragment(recipeAdapter)
var tr = (view.context as FragmentActivity).supportFragmentManager.beginTransaction()
tr.replace(R.id.fragment_container, submitFragment)
tr.commit()
}
browse_recycler_view.apply {
layoutManager = LinearLayoutManager(activity)
adapter = recipeAdapter
}
}
}
When I try to initialize the viewmodel in onViewCreated, I get an IllegalStateException: Can't access ViewModels from detached fragment exception. Creating it in onCreate doesn't work either, since the lifecycle owner is null, which makes sense I guess. What exactly am I doing wrong here?

Related

Problem with data persisting when returning after navigating a fragment

I am repeating the process of adding and completing the list on the detail screen.
The problem is that the previous list remains intact in the newly created detail fragment.
For example, if i made 3 lists in the previous detail screen, adding data in the new detail screen will add them to a list of size 3.
I've tried various things, but I still don't know what could be the cause.
Fragment
class WriteDetailFragment : Fragment() {
...
private val viewModel: WriteDetailViewModel by viewModels {
WriteDetailViewModelFactory(
(requireActivity().application as WorkoutApplication).writeDetailRepo
)
}
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
_binding = FragmentWriteDetailBinding.inflate(inflater, container, false)
binding.apply {
adapter = DetailAdapter()
rv.adapter = adapter
rv.itemAnimator = null
// add set
addSet.setOnClickListener {
viewModel.addSet()
}
// complete
complete.setOnClickListener {
findNavController().navigate(R.id.action_writeDetailFragment_to_addRoutineFragment)
}
}
return binding.root
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
viewLifecycleOwner.lifecycleScope.launch {
repeatOnLifecycle(Lifecycle.State.STARTED) {
viewModel.items.collect { list ->
adapter.submitList(list)
}
}
}
}
}
ViewModel
class WriteDetailViewModel(
private val repository: WriteDetailRepository
): ViewModel() {
private var _items: MutableStateFlow<List<WorkoutSetInfo>> = MutableStateFlow(listOf())
val items = _items.asStateFlow()
fun addSet() {
viewModelScope.launch(Dispatchers.IO) {
repository.add()
_items.value = repository.getList()
}
}
}
Repository
class WriteDetailRepository(val dao: WorkoutDao) {
private var setInfoList = ArrayList<WorkoutSetInfo>()
private lateinit var updatedList: List<WorkoutSetInfo>
fun add() {
val item = WorkoutSetInfo(set = setInfoList.size + 1)
setInfoList.add(item)
updatedList = setInfoList.toList()
}
fun getList() : List<WorkoutSetInfo> = updatedList
}

How to implement a dynamic list view inside fragment android studio in Kotlin

I have two fragments that share information with each other, in the first one I have an edit text and button widget. The second fragment is just a listview. When the user clicks the button, it displays whatever is in the edit text widget in the second fragment.
So if the user enters the text study and clicks the button the second fragment will display
Study
If the user then enters the text eat and clicks the button, the second fragment will display
Study
Eat
I am having so issues with displaying the texts
So far this is what I have done
class FirstFragment : Fragment() {
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?): View? {
viewModel = activity?.run { ViewModelProvider(this)[MyViewModel::class.java]
} ?: throw Exception("Invalid Activity")
val view = inflater.inflate(R.layout.one_fragment, container, false)
val button = view.findViewById<Button>(R.id.vbutton)
val value = view.findViewById<EditText>(R.id.textView)
button.setOnClickListener {
}
return view;
}
}
class SecondFragment : Fragment() {
lateinit var viewModel: MyViewModel
#SuppressLint("MissingInflatedId")
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?): View? {
viewModel = activity?.run { ViewModelProvider(this)[MyViewModel::class.java]
} ?: throw Exception("Invalid Activity")
val view = inflater.inflate(R.layout.page3_fragment, container, false)
val valueView = v.findViewById<TextView>(R.id.textView)
return view
The problem I am having is how to display the texts
If I undestand you correctly, you want to share data between fragments? If yes, you can do that with "shared" viewModel. For example:
class FirstFragment : Fragment() {
private var _binding: FragmentFirstBinding? = null
private val binding get() = _binding!!
private val sharedViewModel by activityViewModels<SharedViewModel>()
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View {
_binding = FragmentFirstBinding.inflate(inflater, container, false)
binding.buttonChangeFragment.setOnClickListener {
/*
You can change data here, or in navigateWithNavController() from
activity (You already have an instance of your viewModel in activity)
*/
sharedViewModel.changeData(binding.myEditText.text.toString())
if (requireActivity() is YourActivity)
(requireActivity() as YourActivity).navigateWithNavController()
}
return binding.root
}
}
class SecondFragment : Fragment() {
private var _binding: FragmentSecondBinding? = null
private val binding get() = _binding!!
private val sharedViewModel by activityViewModels<SharedViewModel>()
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View {
_binding = FragmentSecondBinding.inflate(inflater, container, false)
binding.secondFragmentText.text = sharedViewModel.someData.value
return binding.root
}
}
and your activity:
class YourActivity: AppCompatActivity() {
private lateinit var binding: YourActivityBinding
private lateinit var appBarConfiguration: AppBarConfiguration
private val sharedViewModel: SharedViewModel by lazy {
ViewModelProvider(
this
)[SharedViewModel::class.java]
}
private lateinit var navController: NavController
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
binding = YourActivityBinding.inflate(LayoutInflater.from(this))
setContentView(binding.root)
navController = this.findNavController(R.id.nav_host_fragment)
appBarConfiguration = AppBarConfiguration(navController.graph)
}
/*
This function is just for test
*/
fun navigateWithNavController() {
navController.navigate(R.id.secondFragment)
}
override fun onSupportNavigateUp(): Boolean {
return NavigationUI.navigateUp(navController, appBarConfiguration)
}
}
And your viewModel should look something like this:
class SharedViewModel : ViewModel() {
private val _someData = MutableLiveData("")
val someData: LiveData<String>
get() = _someData
fun changeData(newData: String?) {
_someData.value = newData ?: _someData.value
}
}
Your view model should have a backing list of the entered words. When a word is added, the list can be updated, and in turn you can update a LiveData that publishes the latest version of the list.
class MyViewModel: ViewModel() {
private val backingEntryList = mutableListOf<String>()
private val _entryListLiveData = MutableLiveData("")
val entryListLiveData : LiveData<String> get() = _entryListLiveData
fun addEntry(word: String) {
backingEntryList += word
_entryListLiveData.value = backingEntryList.toList() // use toList() to to get a safe copy
}
}
Your way of creating the shared view model is the hard way. The easy way is by using by activityViewModels().
I also suggest using the Fragment constructor that takes a layout argument, and then setting things up in onViewCreated instead of onCreateView. It's less boilerplate code to accomplish the same thing.
In the first fragment, you can add words when the button's clicked:
class FirstFragment : Fragment(R.layout.one_fragment) {
private val viewModel by activityViewModels<MyViewModel>()
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
val button = view.findViewById<Button>(R.id.vbutton)
val value = view.findViewById<EditText>(R.id.textView)
button.setOnClickListener {
viewModel.addEntry(value.text.toString())
}
}
}
In the second fragment, you observe the live data:
class SecondFragment : Fragment(R.layout.page3_fragment) {
private val viewModel by activityViewModels<MyViewModel>()
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
val valueView = view.findViewById<TextView>(R.id.textView)
viewModel.entryListLiveData.observe(viewLifecycleOwner) { entryList ->
valueView.text = entryList.joinToString(" ")
}
}
}

ListAdapter is not being notified whenever data is updated and emitted by StateFlow

StateFlow is emitting new data after change, but ListAdapter is not being updated/notified, but when configuration is changed(i.e device is rotated from Portrait to Landscape mode) update is occurred:
class TutorialListFragment : Fragment() {
private lateinit var binding: FragmentTutorialListBinding
private val viewModel: ITutorialViewModel by viewModels<TutorialViewModelImpl>()
private lateinit var adapter: TutorialAdapter
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View {
binding = FragmentTutorialListBinding.inflate(inflater, container, false)
return binding.root
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
val recyclerView = binding.recyclerView
adapter = TutorialAdapter()
recyclerView.adapter = adapter
loadData()
}
private fun loadData() {
viewModel
.getTutorialList()
val tutorialList: MutableList<TutorialResponse> = mutableListOf()
viewModel
.tutorialListStateFlow
.onEach { list ->
list.forEach {tutorialResponse->
tutorialList.add(tutorialResponse)
Log.e("TUTORIAL_LIST_FRAG", "$tutorialResponse")
}
adapter.submitList(tutorialList)
}.launchIn(viewLifecycleOwner.lifecycleScope)
}
}
View model is:
class TutorialViewModelImpl: ViewModel(), ITutorialViewModel {
private val mTutorialRepository: ITutorialRepository = TutorialRepositoryImpl()
private val _tutorialListStateFlow = MutableStateFlow<List<TutorialResponse>>(mutableListOf())
override val tutorialListStateFlow: StateFlow<List<TutorialResponse>>
get() = _tutorialListStateFlow.asStateFlow()
init {
mTutorialRepository
.getTutorialListSuccessListener {
viewModelScope
.launch {
_tutorialListStateFlow.emit(it)
Log.e("TUTORIAL_GL_VM", "$it")
}
}
}
override fun getTutorialList() {
// Get list
mTutorialRepository.getTutorialList()
}
}
When I look into Logcat I see this line:
Log.e("TUTORIAL_GL_VM", "$it")
prints all the changes, but no update in ListAdapter.
I assume your data from mTutorialRepository is not a flow ,so you must add .toList() if you want to emit list in stateFlow to get notified
mTutorialRepository.getTutorialListSuccessListener {
viewModelScope.launch {
// here add .toList()
_tutorialListStateFlow.emit(it.toList())
}
}
or if it still does not works, try to change your loadData() like this
private fun loadData() {
// idk what are doing with this ??
viewModel.getTutorialList()
lifecycleScope.launch {
viewModel.tutorialListStateFlow.collect { list ->
adapter.submitList(list)
}
}
}

Android - I can access ViewModel method from fragment but the method does not return the list

I recently started studying android kotlin and I am expecting this to have a very simple answer but I have a ViewModel which has a method called getDataComment and I want to call the method from my fragment and provide the needed argument for it. But when I try to call it, there's no build error, it just doesn't show the list.
My method in view model:
fun getDataComment(postId: Int) {
PostRepository().getDataComment(postId).enqueue(object : Callback<List<Comment>>{
override fun onResponse(call: Call<List<Comment>>, response: Response<List<Comment>>) {
val comments = response.body()
comments?.let {
mPostsComment.value = comments!!
}
}
override fun onFailure(call: Call<List<Comment>>, t: Throwable) {
Log.e(TAG, "On Failure: ${t.message}")
t.printStackTrace()
}
})
}
Fragment Class
class PostDetailFragment : Fragment() {
var param2: Int = 0
private lateinit var binding: FragmentPostDetailBinding
private val viewModel by viewModels<PostCommentViewModel>()
private val gson: Gson by lazy {
Gson()
}
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View {
binding =
DataBindingUtil.inflate(inflater, R.layout.fragment_post_detail, container, false)
return binding.root
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
checkArguments()
}
private fun checkArguments() {
arguments?.let { bundle ->
if (bundle.containsKey("POST")) {
val postString = bundle.getString("POST", "")
val post: Post = gson.fromJson(postString, Post::class.java)
binding.postDetailstvTitle.text = post.title
binding.postDetailstvBody.text = post.body
param2 = post.id
viewModel.getDataComment(param2)
}
}
}
}
Here's what it's supposed to look like: 1
Here's what I'm getting: 2
Sorry in advance if It's messy this is my first time asking here and let me know if you need more information. Thank you!
observe mPostsComment inside fragment from viewmodel
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
checkArguments()
viewModel.mPostsComment.observe(viewLifecycleOwner, { collectionList ->
// do whatever you want with collectionList
})
}

Is it normal for the ViewModel class to be called without setValue on LiveData?

I am studying the MVVM pattern.
I have a question regarding LiveData while using ViewModel class.
Even if I do not change the value of LiveData with setValue or postValue, it continues to observe and execute the fragment.
When addRoutine() is called, vm.observe also continues to run.
As you can see there is no setValue or postValue in addRoutine(), so LiveData has no value change at all.
But why does vm.observe keep running?
This is my code.
ViewModel.kt
class WriteRoutineViewModel : ViewModel() {
private val _items: MutableLiveData<List<RoutineModel>> = MutableLiveData(listOf())
private val rmList = arrayListOf<RoutineModel>()
val items: LiveData<List<RoutineModel>> = _items
fun addRoutine(workout: String) {
val rmItem = RoutineModel(UUID.randomUUID().toString(), workout, "TEST")
rmItem.getSubItemList().add(RoutineDetailModel("2","3","3123"))
rmList.add(rmItem)
// _items.postValue(rmList)
}
fun getListItems() : List<RoutineItem> {
val listItems = arrayListOf<RoutineItem>()
for(testRM in rmList) {
listItems.add(RoutineItem.RoutineModel(testRM.id,testRM.workout,testRM.unit))
val childListItems = testRM.getSubItemList().map { detail ->
RoutineItem.DetailModel("2","23","55")
}
listItems.addAll(childListItems)
}
return listItems
}
}
Fragment
class WriteRoutineFragment : Fragment() {
private var _binding : FragmentWriteRoutineBinding? = null
private val binding get() = _binding!!
private val vm : WriteRoutineViewModel by viewModels { WriteRoutineViewModelFactory() }
private lateinit var epoxyController : RoutineItemController
override fun onCreateView(inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?): View? {
_binding = FragmentWriteRoutineBinding.inflate(inflater, container, false)
return binding.root
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
getTabPageResult()
// RecyclerView(Epoxy) Update
vm.items.observe(viewLifecycleOwner) { updatedItems ->
epoxyController.setData(vm.getListItems())
}
}
private fun getTabPageResult() {
val navController = findNavController()
navController.currentBackStackEntry?.also { stack ->
stack.savedStateHandle.getLiveData<String>("workout")?.observe(
viewLifecycleOwner, Observer { result ->
vm.addRoutine(result)
stack.savedStateHandle?.remove<String>("workout")
}
)
}
}
}

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