Hold data from EventListener in MutableLiveData - android

I'm trying to retrive data from firestore and want to keep it in shared view model. Basically I have a main activity and 2 fragments that need to retrieve data from shared view model of main activity. My current method is :
class SharedViewModel: ViewModel() {
private val firebaseUtils = FirebaseUtils()
fun getTempWords(localeLearn: String): LiveData<DocumentSnapshot> {
val document = firebaseUtils.getTempWordsLocaleRef(localeLearn)
return FirebaseDocumentLiveData(document)
}}
What i want is that just retrive data once and keep it in MutableLiveData and pass to fragmetns.
Edit:
What I'm done is:
var tempWords : MutableLiveData<DocumentSnapshot> = MutableLiveData()
fun getTemp(localeLearn: String): LiveData<DocumentSnapshot> {
if (tempWords.value == null) {
val document = firebaseUtils.getTempWordsLocaleRef(localeLearn)
tempWords = FirebaseDocumentLiveData(document)
}
return tempWords
}
But if i kill the fragment and recreate it again, it calls EventListener in FirebaseDocumentLiveData(document) class again.
Edit 2:
My Fragment
private lateinit var model: SharedViewModel
override fun onCreate(savedInstanceState: Bundle?) {
//
model = activity?.run {
ViewModelProviders.of(this).get(SharedViewModel::class.java)
} ?: throw Exception("Invalid Activity")
}
//
model.getTemp(mLocaleLearn!!).observe(this, Observer {...}

What is the question? it looks like you successfully made it.
You ask how you can access the data from your fragments?
in view model class
private final MutableLiveData<Item> data = new MutableLiveData<Item>();
in your fragments:
model = ViewModelProviders.of(getActivity()).get(SharedViewModel.class);

Related

How to update Room database in Android

In my application I want use MVI for application architecture and I should use Room database.
I have one activity and one fragment!
In fragment I receive data from user and save into database and in activity show this data into recyclerview.
I write below codes and my data successfully save into database!
But for show it into activity, I should exit from application and enter to show data list!
I want without exit from application, update automatically this list.
Dao codes :
#Query("SELECT * FROM my_table")
fun getAllData(): MutableList<Entity>
Repository codes:
class MyRepository #Inject constructor(private val dao: DataDao) {
fun allData() = dao.getAllData()
}
ViewModel codes:
#HiltViewModel
class MyViewModel #Inject constructor(private val repository: MyRepository) : ViewModel() {
val mainIntent = Channel<MainIntent>()
private val _state = MutableStateFlow<MainState>(MainState.Idle)
val state : StateFlow<MainState> get() = _state
init {
handleIntent()
}
private fun handleIntent() {
viewModelScope.launch {
mainIntent.consumeAsFlow().collect{
when(it){
is MainIntent.LoadAllData-> fetchingAllDataList()
}
}
}
}
private fun fetchingAllDataList() {
viewModelScope.launch {
_state.value = MainState.LoadData(repository.allData())
}
}
}
Activity codes :
lifecycleScope.launch {
//Send
viewModel.mainIntent.send(MainIntent.LoadAllData)
//Get
viewModel.state.collect { state ->
when (state) {
is MainState.Idle -> {}
is MainState.LoadData -> {
dataAdapter.setData(state.list)
fataList.apply {
layoutManager = StaggeredGridLayoutManager(2, StaggeredGridLayoutManager.VERTICAL)
adapter = noteAdapter
}
}
}
}
}
How can I fix this problem?
Several methods below can solve this problem.
Use EventBus. Send an EventBus message after saving data to database in fragment and handle this message in MyViewModel or your Activity to reload data
In your 'dao' interface, change function return type to LiveData: fun getAllData(): LiveData<MutableList<Entity>>. When related data changed in database, Room database automaticly notify changes to Observers. Check this
Use Broadcast like using EventBus
If fragment is contained in the Activity which requires the notification when data changed, use SharedViewModel to notify activity.
class MyFragment: BottomDialogSheetFragment {
var entityChangeListener: IEntityChangeListener? = null
...
// after saving data to database
entityChangeListener?.onChanged()
}
class MyActivity {
fun showDialog() {
val fragment = MyFragment()
fragment.entityChangeListener = object : IEntityChangeListener {
override fun onChanged() {
// change [fetchAllDataList] function to public
myViewModel.fetchAllDataList()
}
}
}
}
interface IEntityChangeListener {
fun onChanged()
}
// using SharedViewModel
class MyFragment: BottomDialogSheetFragment {
var entityViewModel by sharedViewModel<EntityViewModel>
...
// saving entity data
entityViewModel.saveData(entities)
}
class MyActivity {
// shared view model for entity database business
val entityViewModel by viewModels<EntityViewModel>
// viewmodel for other business logic
val viewModel by viewModels<MyViewModel>
}
class EntityViewModel: ViewModel(){
...
private val _state = MutableStateFlow<MainState>(MainState.Idle)
val state : StateFlow<MainState> get() = _state
fun fetchingAllDataList() {
viewModelScope.launch(Dispatchers.IO) {
_state.value = MainState.LoadData(repository.allData())
}
}
fun saveData(entities: List<Entity>) {
dao.save(entities)
fetchingAllDataList()
}
}

Cannot reassign variable inside observer viewmodel

So I created MVVM app in kotlin to fetch movies from TMDB api, using injections and coroutines.
My problem is that I cannot copy the list of returned movies into a new list I created or reassign any variables inside the livedata observer from the MainActivity the values of variables stays the same as they were after exit the scope.
MainActivity class:
#AndroidEntryPoint
class MainActivity : AppCompatActivity() {
private lateinit var binding:ActivityMainBinding
private val viewModel:MoviesViewModel by lazy {
ViewModelProvider(this)[MoviesViewModel::class.java]
}
private lateinit var list: MutableList<Movies>
private var number:Int=1
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
binding=ActivityMainBinding.inflate(layoutInflater)
setContentView(binding.root)
getData()
list
number
}
private fun getData(){
list= mutableListOf()
viewModel.getData(page = "1").observe(this#MainActivity,Observer{ item ->
item?.let { res ->
when (res.status) {
Status.SUCCESS -> {
var tmpList = item.data?.body()?.results
list= tmpList!!.toMutableList()
number+=1
}
Status.ERROR -> {
res.message?.let { Log.e("Error", it) }
}}}
})}}
ViewModel class:
class MoviesViewModel #ViewModelInject constructor(var repository: MoviesRepository): ViewModel() {
fun getData(page:String)= liveData(Dispatchers.IO){
emit(Resource.loading(data = null))
try {
emit(Resource.success(data=repository.getMovies(api_key = Constants.API_KEY,
start_year=Constants.START_YEAR, end_year = Constants.END_YEAR,page = page)))
}catch (e:Exception){
emit(e.message?.let { Resource.error(message = it, data = null) })
}
}
}
As you can see I tried to change the value of number and load the list into my new list but outside the scope the values returned to be what they were before.
Very thankful for anyone who can assist.
Update:
So I tried to initialized all the items inside the success case and it worked I guess there is no other way to change the values outside the scope.

ViewModel not initializing or problem design with my viewModel

I've been reading some questions, answers and blogs about MVVM pattern in Android, and I've implemented it in my application.
My application consists of a MainActivity with 3 Tabs. Content of each tab is a fragment.
One of these fragments, is a List of Users stored on Room DB, which is where I've implemented the MVVM (implementing User object, ViewModel, Repository and Adapter with RecycleView).
In this same fragment, I have an "add User" button at the end that leads to a new activity where a formulary is presented to add a new user. In this activity I want to be sure that the full name of user not exists in my DB before saving it.
I was trying to use the same ViewModel to get full UserNames full name, but it seems that ViewModel is never initialized and I dont' know why.
I've read some questions about that viewmodel can't be used in different activities (I use it in MainActivity also in AddUser activity
This is my ViewModel:
class UserViewModel : ViewModel() {
val allUsersLiveData: LiveData<List<User>>
private val repository: UserRepository
init {
Timber.i("Initializing UserViewModel")
repository = UserRepository(UserTrackerApplication.database!!.databaseDao())
allUsersLiveData = repository.getAllUsers()
}
fun getAllUsersFullName(): List<String> {
return allUsersLiveData.value!!.map { it.fullname}
}
And my AddUser activity:
class AddUser : AppCompatActivity() {
private lateinit var userList:List<String>
private lateinit var binding: ActivityAddUserBinding
private val userViewModel: UserViewModel by viewModels()
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_add_user)
Timber.i("Add User OnCreate")
binding = ActivityAddUserBinding.inflate(layoutInflater)
setContentView(binding.root)
}
fun addUserClick(v : View){
//someCode
val userName = binding.constraintLayoutAddUser.etUserName!!.text.toString()
if(checkUserExistance(userName)) {
val text: String = String.format(
resources.getString(R.string.repeated_user_name),
userName
Snackbar.make(v, text, Snackbar.LENGTH_LONG).show()
{
else
{
lifecycleScope.launch {
UserTrackerApplication.database!!.databaseDao()
.insertUser(user)
Timber.i("User added!")
}
finish()
}
}
Debugging, I see the log "Initializing UserViewModel" when the fragment of MainActivity is started, but I can't see it when AddUser activity is called. So it seems it's not initializing correctly.
So the questions:
Is this a good approach? I'm making some design mistake?
Why the VM isn't initializing?
EDIT
I forgot to add this function. Calling userViewModel here is where I get the error:
private fun checkUserExistance(userName: String): Boolean {
var result = false
userList = userViewModel.getAllUsersNames()
for (usr in userList)
{
if(usr.uppercase() == userName.uppercase())
{
result = true
break
}
}
return result
}
EDIT 2
I added this on my "onCreate" function and started to work:
userViewModel.allUsersLiveData.observe(this, Observer<List<User>>{
it?.let {
// updates the list.
Timber.i("Updating User Names")
userList =userViewModel.getAllUsersNames()
}
})
if you take a look at by viewModels delegate you will see it's lazy it means it will initialize when it is first time accessed
#MainThread
public inline fun <reified VM : ViewModel> ComponentActivity.viewModels(
noinline factoryProducer: (() -> Factory)? = null
): Lazy<VM> {
val factoryPromise = factoryProducer ?: {
defaultViewModelProviderFactory
}
return ViewModelLazy(VM::class, { viewModelStore }, factoryPromise)
}

MutableLiveData ArrayList is empty even after postValue() Kotlin

I am now stuck and currently wondering why my mutable arraylist returns null even if it is being updated with postvalue(). I tried to display it using Toast and it displayed [] which I think is null. It had no space in between so it looked like a box. I did toString() it as well in order to show the text. How would I be able to solve this problem?
Here is my Main Activity:
val list = ArrayList<String>()
list.add("text1")
list.add("text2")
val viewmodel = ViewModelProviders.of(this).get(viewmodel::class.java)
viewmodel.Testlist.postValue(list)
ViewModel:
class viewmodel: ViewModel() {
val Testlist: MutableLiveData<ArrayList<String>> = MutableLiveData()
init {
Testlist.value = arrayListOf()
}
}
Fragment:
Top area:
activity?.let {
val viewmodel = ViewModelProviders.of(this).get(viewmodel::class.java)
observeInput(viewmodel)
}
Bottom area:
private fun observeInput(viewmodel: viewmodel) {
viewmodel.Testlist.observe(viewLifecycleOwner, Observer {
it?.let {
Toast.makeText(context, it.toString(), Toast.LENGTH_LONG).show()
}
})
}
You post the value to the LiveData object in the activity's viewmodel, which isn't the same instance as the fragment's viewmodel. Let's take look at the way you instantiate the viewmodel in your fragment:
activity?.let {
// activity can be refered by the implicit parameter `it`
// `this` refers to the current fragment hence it's the owner of the view model
val viewmodel = ViewModelProviders.of(this).get(viewmodel::class.java)
observeInput(viewmodel)
}
To get a viewmodel that is shared between your activity and fragment you have to pass the activity as its owner:
activity?.let { val viewmodel = ViewModelProviders.of(it).get(viewmodel::class.java) }
Probably you can see developer guide example to resolve your problem
https://developer.android.com/topic/libraries/architecture/viewmodel.html#kotlin
// shared viewmodel
class SharedViewModel : ViewModel() {
private val usersList: MutableLiveData<List<String>>()
fun getUsers(): LiveData<List<String>> {
return usersList
}
fun setUsers(users: List<String>) {
usersList.value = users
}
}
// Attach ViewModel In Activity onCreate()
val model = ViewModelProviders.of(this)[SharedViewModel::class.java]
val list = arrayListOf<String>()
list.add("user1")
list.add("user2")
model.setUsers(list)
// Get same ViewModel instance In fragment onCreateView()
model = activity?.run {
ViewModelProviders.of(this)[SharedViewModel::class.java]
} ?: throw Exception("Invalid Activity")
model.getUsers().observe(this, Observer<List<User>>{ users ->
// update UI
})
You can use this :
fun <T : Any?> MutableLiveData<ArrayList<T>>.default(initialValue: ArrayList<T>) = apply { setValue(initialValue) }
and then use this function as below:
viewmodel.Testlist.default(ArrayList())
For me, I have a BaseActivity that other activities extend from it :
class UAppCompatActivity : AppCompatActivity() {
protected fun <T : Any?> MutableLiveData<ArrayList<T>>.default(initialValue: ArrayList<T>) = apply { setValue(initialValue) }
protected fun <T> MutableLiveData<ArrayList<T>>.addItem(item: T) {
val updatedItems = this.value as ArrayList
updatedItems.add(item)
this.value = updatedItems
}
protected fun <T> MutableLiveData<ArrayList<T>>.deleteItem(item: T) {
val updatedItems = this.value as ArrayList
updatedItems.remove(item)
this.value = updatedItems
}
...
have you used the same instance of your view model? or have you defined another view model in the fragment class? The issue could be that you're accessing a different instance of the view model and not the one were the MutableLiveData was updated

How to update Room database in Kotlin without activity refreshing?

I'm fairly new to Kotlin/Android development, and am trying to figure out the best way to update data in a Room database. After following some tutorials, I currently have an architecture that looks like this:
Room Database with tables and DAOs -> Repository -> ViewModel -> Activity
So the activity has a ViewModel that calls the Repository, which in turn updates the database.
The ViewModel for the activity has a LiveData list of the object (there's also a factory to create the ViewModel, but that's just to allow the bookId to be passed in):
class ViewBookViewModel(application: Application, bookId: Int) : AndroidViewModel(application) {
private val repository: AppRepository
internal val flashCards: LiveData<List<FlashCard>>
init {
val flashCardDao = AppDatabase.getDatabase(application, viewModelScope).flashCardDao()
val bookDao = AppDatabase.getDatabase(application, viewModelScope).bookDao()
repository = AppRepository(flashCardDao, bookDao)
flashCards = flashCardDao.getByBookId(bookId)
}
fun insert(flashCard: FlashCard) = viewModelScope.launch(Dispatchers.IO){
repository.insert(flashCard)
}
fun setIsFavorited(cardUid: Long, favorited: Boolean) = viewModelScope.launch(Dispatchers.IO) {
repository.setIsFavorited(cardUid, favorited)
}
}
//The actual query that gets called eventually
#Query("UPDATE flashcard SET is_favorited = :favorited WHERE uid LIKE :cardUid")
fun setFavorited(cardUid: Long, favorited: Boolean)
And the Activity sets up the viewModel and also creates an observer on the
class ViewBookActivity : AppCompatActivity() {
private lateinit var flashCards: LiveData<List<FlashCard>>
private var layoutManager: RecyclerView.LayoutManager? = null
private lateinit var viewModel: ViewBookViewModel
private var bookId: Int = 0
private lateinit var bookTitle: String
override fun onCreate(savedInstanceState: Bundle?) {
...
bookId = intent.extras["bookId"] as Int
bookTitle = intent.extras["bookTitle"].toString()
layoutManager = LinearLayoutManager(this)
flashCardRecyclerView.layoutManager = layoutManager
viewModel = ViewModelProviders.of(this, ViewBookViewModelFactory(application, bookId as Int)).get(ViewBookViewModel::class.java)
flashCards = viewModel.flashCards
flashCards.observe(this, Observer { flashCards:List<FlashCard> ->
flashCardRecyclerView.adapter = FlashCardRecyclerAdapter(flashCards, viewModel)
})
}
}
Finally, I have a custom RecyclerAdapter, which is where I'm running into trouble. I have it set up so that when the user taps the "favorite" button on the Flash Card, it updates the database. However, this also causes the Activity to "refresh", scrolling to the top. I assume this is because it is observing LiveData, and that data is being changed.
custom RecylcerAdapter with ViewHolder code (stripped not-relevant code):
class FlashCardRecyclerAdapter(val flashCards: List<FlashCard>, val viewModel: ViewBookViewModel) : RecyclerView.Adapter<FlashCardRecyclerAdapter.FlashCardViewHolder>() {
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): FlashCardViewHolder {
val v: View = LayoutInflater
.from(parent.context)
.inflate(R.layout.flash_card, parent, false)
return FlashCardViewHolder(v)
}
override fun onBindViewHolder(holder: FlashCardViewHolder, position: Int) {
val card = flashCards[position]
holder.isFavorited = card.isFavorited
holder.uid = card.uid
holder.modifyFavoriteButtonImage(holder.isFavorited)
}
override fun getItemCount(): Int {
return flashCards.size
}
inner class FlashCardViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView){
var mFavorited: Button
var frontShowing: Boolean
var isFavorited: Boolean = false
var uid: Long = 0
init {
mFavorited = itemView.findViewById(R.id.favoriteButton)
mFavorited.setOnClickListener { _ ->
isFavorited = !isFavorited
viewModel.setIsFavorited(uid, isFavorited) // Here is the database call
modifyFavoriteButtonImage(isFavorited)
}
}
fun modifyFavoriteButtonImage(isFavorited: Boolean){
// Code removed, just updates the image to be a filled/empty star based on favorited status
}
}
I feel like I am probably doing something wrong, as passing the ViewModel into the recylcer adapter in order to update the DB does not seem correct. Is there a pattern I should be using for this sort of situation, or should I change the code to not be using LiveData? Any help would be greatly appreciated.
flashCards.observe(this, Observer { flashCards:List<FlashCard> ->
flashCardRecyclerView.adapter = FlashCardRecyclerAdapter(flashCards, viewModel)
}
you should not be making a new adapter instance here, instead, assign the values you get from the live data to the existing adapter (adapter.flashCards = flashCards, LiveData value) and call adapter.notifyDataSetChanged, this will tell your adapter that new data came in and it needs to update.
you should not be passing your ViewModel to your adapter (or anything).
you can do something like this instead:
class FlashCardRecyclerAdapter(val flashCards: List<FlashCard>, val callback:(FlashCard) -> Unit)
then, where you declare your adapter, you do this :
val adapter = FlashCardRecyclerAdapter(...) {
viewModel.update(it)
}
and then :
override fun onBindViewHolder(holder: FlashCardViewHolder, position: Int) {
val card = flashCards[position]
holder.isFavorited = card.isFavorited
holder.uid = card.uid
holder.itemView.setOnClickListener {
callback.invoke(card)
}
holder.modifyFavoriteButtonImage(holder.isFavorited)
}
In your repository method, I am not sure what you are doing there but rather than passing in a livedata instance, you should pass in the underlying data of the livedata instance. That way, the observer in the main activity doesn't get triggered everytime you call setIsFavorited(). If you do want to trigger the observer, then you can just call postValue() on the livedata instance. As for the adapter question, I do not know the best practices but I usually create a listener interface so I don't have to pass around my viewmodels everywhere. All of my viewmodels are contained within my fragments and never goes anywhere else. Let me know if this answers your questions.
Also, if you are using viewmodels with recyclerview, consider using list adapters. They are made to work seamlessly with viewmodels. https://developer.android.com/reference/android/support/v7/recyclerview/extensions/ListAdapter
It makes it much simpler to use viewmodels with recyclerview.

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