I have a RecyclerView displaying data from a Dao.
In the data that is shown in the recyclerView is a button with which the item should get deleted.
I know the function for that is :
fun deleteReceipt(receipts: Receipts) = viewModelScope.launch {
receiptDao.delete(receipts)
}
But I am not quite sure where to put it and call it. Because if I want to call it in the Adapter where i set the other displayed Item values I have no access to the Dao
Here is the fragment:
#AndroidEntryPoint
class HistoryFragment : Fragment(R.layout.fragment_history) {
private val viewModel: PurchaseViewmodel by viewModels()
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
val binding = FragmentHistoryBinding.bind(view)
val exampleAdapter = ExampleAdapter()
binding.apply{
recyclerView.apply{
layoutManager = LinearLayoutManager(requireContext())
adapter = exampleAdapter
setHasFixedSize(true)
}
}
setFragmentResultListener("add_receipt_request"){_,bundle ->
val result = bundle.getInt("add_receipt_request")
viewModel.onAddResult(result)
}
viewModel.receipts.observe(viewLifecycleOwner){ /// New Items get passed to the List
exampleAdapter.submitList(it)
}
}
}
The ViewModel:
#HiltViewModel
class PurchaseViewmodel #Inject constructor(
private val receiptDao: ReceiptDao
): ViewModel() {
private val tasksEventChannel = Channel<TasksEvent>()
val addTaskEvent = tasksEventChannel.receiveAsFlow()
val receipts = receiptDao.getAllReceipts().asLiveData()
fun onAddResult(result: Int){
when (result){
ADD_RECEIPT_RESULT_OK ->showReceiptSavedConfirmation("Receipt is saved")
}
}
private fun showReceiptSavedConfirmation (text: String) = viewModelScope.launch {
tasksEventChannel.send(TasksEvent.ShowReceiptSavedConfirmation(text))
}
fun deleteReceipt(receipts: Receipts) = viewModelScope.launch {
receiptDao.delete(receipts)
}
sealed class TasksEvent {
data class ShowReceiptSavedConfirmation(val msg: String) : TasksEvent()
}
}
And the Adapter:
class ExampleAdapter : ListAdapter<Receipts,ExampleAdapter.ExampleViewHolder>(DiffCallback()) {
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ExampleViewHolder { // Basically how to get a new Item from the List and display it
val binding = ReceiptsBinding.inflate(LayoutInflater.from(parent.context),parent,false)
return ExampleViewHolder(binding)
}
override fun onBindViewHolder(holder: ExampleViewHolder, position: Int) {
val currentItem = getItem(position)
holder.bind(currentItem)
}
override fun getItemCount(): Int {
return super.getItemCount()
}
class ExampleViewHolder(private val binding: ReceiptsBinding) : RecyclerView.ViewHolder(binding.root){ //Examples One Row in our list
fun bind (receipts: Receipts) {
binding.apply {
storeHistory.text = receipts.store
amountHistory.text = receipts.total
dateHistory.text = receipts.date
}
}
}
class DiffCallback : DiffUtil.ItemCallback<Receipts>() {
override fun areItemsTheSame(oldItem: Receipts, newItem: Receipts) =
oldItem.id == newItem.id
override fun areContentsTheSame(oldItem: Receipts, newItem: Receipts) =
oldItem == newItem
}
}
Create a listener using Interface
Implement the listener in Fragment
Create listener variable in Adapter
pass the listener from fragment to adapter
pass the listener to viewHolder
on Delete button click of that item call the listener method, which will trigger the implementation in Fragment where you have access to your ViewModel
delete the receipt using viewModel.deleteReceipt
Related
when i try to delete first row i get first row back and with duplicate second row
enter image description here
after delete any row from the list gives me duplicate data like this
enter image description here
This is my Adapter class. On my deleteItem function position is passed from fragment class and
it is supposed to delete an item from the given position and update the list but its rendering the duplicate data.
class MyListAdapter :ListAdapter<Article,MyListAdapter.MyViewHolder>(MyDiffUtil()) {
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): MyViewHolder {
val view = LayoutInflater.from(parent.context).inflate(R.layout.recycler_item,parent,false)
return MyViewHolder(view)
}
override fun onBindViewHolder(holder: MyViewHolder, position: Int) {
val item = getItem(position)
holder.onBind(item)
// to click each item of list
holder.itemView.setOnClickListener {
onItemClickListener?.let {it(item) }
}
}
class MyViewHolder(itemView :View) : RecyclerView.ViewHolder(itemView)
{
fun onBind(article: Article) = with(itemView)
{
Glide.with(this)
.load(article.urlToImage)
.error(R.drawable.notfound)
.into(imageView)
webSource.text = article.source?.name
newsDate.text = article.publishedAt
newsTitle.text = article.title
newsDescription.text = article.description
}
}
// lamda function for handling web view
private var onItemClickListener : ((Article) -> Unit)? = null
fun setOnItemClickListener(listener : (Article) ->Unit)
{
onItemClickListener = listener
}
// implementing diffutil class
class MyDiffUtil : DiffUtil.ItemCallback<Article>()
{
override fun areItemsTheSame(oldItem: Article, newItem: Article): Boolean {
return oldItem.url == newItem.url
}
override fun areContentsTheSame(oldItem: Article, newItem: Article): Boolean {
return oldItem == newItem
}
}
fun deleteItem(pos : Int)
{
var myl = ArrayList<Article>()
val currentList= currentList.toMutableList()
currentList.removeAt(pos)
myl.addAll(currentList)
submitList(myl)
}
}
`
I tried to delete the saved news from the ListAdapter and update the recycler view with animation of DiffUtill class but its not updating the recycler view and
giving duplicate data . How can i delete data with diffutil animation as its normal way. Thanks in advance.
this is my fragment
package com.example.news.Fragments
class SavedNews : Fragment() {
lateinit var mymainViewModel: MainViewModel
lateinit var databaseObject: MyDataBase
lateinit var myAdapter: MyListAdapter
lateinit var convertedArticleList : ArrayList<Article>
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
myAdapter = MyListAdapter()
convertedArticleList = ArrayList()
return inflater.inflate(R.layout.fragment_saved_news, container, false)
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
savedNewsRecyclerView.layoutManager = LinearLayoutManager(activity,LinearLayoutManager.VERTICAL,
false)
savedNewsRecyclerView.adapter = myAdapter
ItemTouchHelper(object :ItemTouchHelper.SimpleCallback(0,ItemTouchHelper.RIGHT){
override fun onMove(
recyclerView: RecyclerView,
viewHolder: RecyclerView.ViewHolder,
target: RecyclerView.ViewHolder
): Boolean {
// this method is called
// when the item is moved.
return true
}
override fun onSwiped(viewHolder: RecyclerView.ViewHolder, direction: Int) {
// this method is called when we swipe our item to right direction.
// on below line we are getting the item at a particular position.
val deletedCourse: Article =
convertedArticleList.get(viewHolder.adapterPosition)
myAdapter.deleteItem(viewHolder.adapterPosition)
mymainViewModel.deleteSavedNews(deletedCourse.id!!)
// myAdapter.notifyItemRemoved(viewHolder.adapterPosition)
// myAdapter.submitList(myCurrentList)
// Snackbar.make(savedNewsRecyclerView,"Deleted" + deletedCourse.title,
// Snackbar.LENGTH_LONG).setAction(
// "Undo",
// View.OnClickListener {
//
// convertedArticleList.add(position,deletedCourse)
// myAdapter.notifyItemInserted(position)
// }
// ).show()
}
}).attachToRecyclerView(savedNewsRecyclerView)
}
override fun onResume() {
super.onResume()
Log.d("LIFE","ON Resume")
val myInterfaceObject = ApiInterface.MyObject.getInstance()
databaseObject = MyDataBase.MyObjectDB.getDBInstance(activity as MainActivity)
val myRepository = Repository(myInterfaceObject, databaseObject)
mymainViewModel = ViewModelProvider(
this,
MainViewModelFactory(myRepository)
).get(MainViewModel::class.java)
//listAdapter things
// show saved news in savednews fragment
lifecycleScope.launch(Dispatchers.Main) {
//abstract data from saved room database and converting likedartcile datacass object to
// Artticle data class article
mymainViewModel.abstractSavedNews().observe(viewLifecycleOwner, Observer {
it.forEach { eachLikedArticle ->
val obj = toArticle(eachLikedArticle)
convertedArticleList.add(obj)
}
myAdapter.submitList(convertedArticleList)
})
//clicking the item of save news
myAdapter.setOnItemClickListener {
val bundle = Bundle().apply {
putSerializable("article", it)
}
convertedArticleList.clear()
findNavController().navigate(R.id.action_savedNews_to_article, bundle)
}
}
}
private fun toArticle(rawObject: LikedArticle) = Article(
rawObject.author, rawObject.content,
rawObject.description, rawObject.publishedAt, rawObject.source, rawObject.title,
rawObject.url, rawObject.urlToImage, rawObject.id
)
}
There is not enough information to actually replicate how you're trying to use this in your Fragment/Activity but without changing your code too much, this works (note I used view binding):
class MyListAdapter :
ListAdapter<Article, MyViewHolder>(MyDiffUtil()) {
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int) = MyViewHolder(
RecyclerItemBinding.inflate(
LayoutInflater.from(parent.context),
parent,
false
)
)
override fun onBindViewHolder(holder: MyViewHolder, position: Int) {
val item = getItem(position)
holder.onBind(item)
}
fun deleteItem(pos: Int) {
var myl = ArrayList<Article>()
val currentList = currentList.toMutableList()
currentList.removeAt(pos)
myl.addAll(currentList)
submitList(myl)
}
}
class MyViewHolder(private val binding: RecyclerItemBinding) : RecyclerView.ViewHolder(binding.root) {
fun onBind(article: Article) = with(binding) {
textView.text = article.url
}
}
class MyDiffUtil : DiffUtil.ItemCallback<Article>() {
override fun areItemsTheSame(oldItem: Article, newItem: Article): Boolean {
return oldItem.url == newItem.url
}
override fun areContentsTheSame(oldItem: Article, newItem: Article): Boolean {
return oldItem == newItem
}
}
Overall this should work.
You can also refactor deleteItem to something more meaningful:
fun deleteItem(pos: Int) {
val oldList = currentList.toMutableList()
oldList.removeAt(pos)
val updatedList = oldList
submitList(updatedList)
}
I have a RecyclerView with a ListAdapter. The list that is shown in the RecyclerView comes from a Flow that is observed in the Fragment that the recyclerView is instantiated.
When the Fragment is created, the data are calculated too (in onViewCreated Method) .
In the first data-calculation the RecyclerView is empty, a progressBar is shown, then the data is calculated, the progressbar hides, and the RecyclerView is populated.
If I go again in this Fragment to re-calculate the data, the previous list is shown simultaneously with the progressbar, and then is updated.
I want every time that new data is calculated to NOT show the previous list (just like the first data-calculation), but can't find a way to do it.
I tried to clear() the currentList and notifyDataSetChanged() but it still happens.. Any ideas?
Here is the code:
Fagment:
#AndroidEntryPoint
class YourPlanFragment : Fragment(R.layout.fragment_your_plan) {
lateinit var navController: NavController
private lateinit var binding: FragmentYourPlanBinding
private val sharedViewModel: WorkoutPlansViewModel by activityViewModels()
private lateinit var appBarConfiguration: AppBarConfiguration
#Inject
lateinit var dataStore: UserPreferencesRepo
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
navController = Navigation.findNavController(view)
binding = FragmentYourPlanBinding.bind(view)
appBarConfiguration = AppBarConfiguration(navController.graph)
val toolbar = binding.yourPlanToolbar
toolbar.setupWithNavController(navController, appBarConfiguration)
val exerciseAdapter = DayListAdapter(DayListAdapter.OnClickListener {
navigateTo(sharedViewModel.weekIndex, it.dayNumber)
})
exerciseAdapter.currentList.clear()
exerciseAdapter.notifyDataSetChanged()
binding.recyclerViewYourPlan.apply {
adapter = exerciseAdapter
layoutManager = LinearLayoutManager(requireContext())
setHasFixedSize(true)
recycledViewPool.clear()
removeAllViews()
adapter?.notifyDataSetChanged()
}
if (!sharedViewModel.planGenerated) {
// Here the data is generated
sharedViewModel.onTriggerEvent(WorkoutPlansEvent.GetWorkoutPlanEvent)
} else if (sharedViewModel.planGenerated) {
sharedViewModel.onTriggerEvent(WorkoutPlansEvent.GetWeekEvent)
}
viewLifecycleOwner.lifecycleScope.launch {
viewLifecycleOwner.repeatOnLifecycle(Lifecycle.State.STARTED) {
sharedViewModel.yourPlanState.collect { yourPlanState ->
when (yourPlanState.progressBarState) {
is ProgressBarState.Loading -> {
binding.progressBar.isVisible = true
}
is ProgressBarState.Idle -> {
binding.progressBar.isInvisible = true
}
}
exerciseAdapter.submitList(yourPlanState.planDays)
}
}
}
}
private fun navigateTo(
currentWeek: Int,
dayNumber: Int,
) {
val action =
YourPlanFragmentDirections.actionYourPlanFragmentToYourDayFragment(
currentWeek,
dayNumber
)
navController.navigate(action)
}
}
ListAdapter:
class DayListAdapter(private val onClickListener: OnClickListener) :
ListAdapter<Day, DayListAdapter.DayViewHolder>(ExerciseComparator()) {
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): DayViewHolder {
val binding = ListItemDayBinding.inflate(LayoutInflater.from(parent.context), parent, false)
return DayViewHolder(binding)
}
override fun onBindViewHolder(holder: DayViewHolder, position: Int) {
val currentItem = getItem(position)
holder.itemView.setOnClickListener {
onClickListener.onClick(currentItem)
}
if (currentItem != null) {
holder.bind(currentItem)
}
}
class DayViewHolder(private val binding: ListItemDayBinding) :
RecyclerView.ViewHolder(binding.root) {
fun bind(day: Day) {
binding.apply {
dayNumber = day.dayNumber.toString()
executePendingBindings()
}
}
}
class ExerciseComparator : DiffUtil.ItemCallback<Day>() {
override fun areItemsTheSame(oldItem: Day, newItem: Day) =
oldItem.dayNumber == newItem.dayNumber
override fun areContentsTheSame(oldItem: Day, newItem: Day) =
oldItem == newItem
}
class OnClickListener(val clickListener: (day: Day) -> Unit) {
fun onClick(day: Day) = clickListener(day)
}
}
This is happing because of the activityViewModels() that will preserve the viewmodel based on activity lifecycle. Either create WorkoutPlansViewModel using viewmodels() or Try to clear the list from the WorkoutPlansViewModel when you are creating the fragment.
I implemented a ListAdapter with DiffUtil and faced an issue when appending a new list. It overwrites instead of appending to old one. To solve issue i created a new project and populate it with some test data.
Here is my code:
MainActivity
private lateinit var binding: ActivityMainBinding
private val viewModel: ItemViewModel by lazy {
ItemViewModel()
}
private val adapter: ItemAdapter by lazy {
ItemAdapter()
}
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
binding = ActivityMainBinding.inflate(layoutInflater)
setContentView(binding.root)
viewModel.getItems()
viewModel.items.observe(this, Observer { items ->
adapter.submitList(items)
})
binding.recyclerView.adapter = adapter
binding.fab.setOnClickListener {
viewModel.getItems(9)
}
}
ItemViewModel
class ItemViewModel: ViewModel() {
private val repository = FakeRepository()
private val _items: MutableLiveData<List<Item>> = MutableLiveData()
val items: LiveData<List<Item>> = _items
fun getItems(start: Int = 1) {
viewModelScope.launch {
val items = repository.getItems(start)
_items.value = items
/*val newItems = items.map { it.copy() }
_items.postValue(newItems)*/
}
}
}
ItemAdapter
class ItemAdapter: ListAdapter<Item, ItemAdapter.ViewHolder>(DiffUtilCallback()) {
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
return ViewHolder(ItemRowBinding.inflate(LayoutInflater.from(parent.context),parent,false))
}
override fun onBindViewHolder(holder: ViewHolder, position: Int) {
holder.bind(getItem(position))
}
class ViewHolder(private val binding: ItemRowBinding): RecyclerView.ViewHolder(binding.root) {
fun bind(item: Item) {
binding.apply {
title.text = item.title
}
}
}
private class DiffUtilCallback: DiffUtil.ItemCallback<Item>() {
override fun areItemsTheSame(oldItem: Item, newItem: Item) = oldItem.id == newItem.id
override fun areContentsTheSame(oldItem: Item, newItem: Item) = oldItem == newItem
}
}
Item
data class Item(
val id: Int,
val title: String,
val timestamp: String
)
As per documentation:
Submits a new list to be diffed, and displayed.
If a list is already being displayed, a diff will be computed on a
background thread, which will dispatch Adapter.notifyItem events on
the main thread.
So, when you submit a new list via the LiveData observer, it's a brand new list to the adapter, and therefore it overwrites the current items not appending them.
If you want to append the current items, you can create a method in the adapter to consolidate the current list with the new one, and eventually submit it:
class ItemAdapter : ListAdapter<Item, ItemAdapter.ViewHolder>(DiffUtilCallback()) {
//......
fun appendList(list: List<Item>) {
val currentList = currentList.toMutableList() // get the current adapter list as a mutated list
currentList.addAll(list)
submitList(currentList)
}
}
And apply that to the observer callback in the activity:
viewModel.items.observe(this, Observer { items ->
// myAdapter.submitList(items) // send a brand new list
myAdapter.appendList(items) // Update the current list
})
I use ListAdapter as the source of a RecyclerView, it will display a list of MVoice. You can see Code B.
I think I can get the position of a MVoice in ListAdapter, so I can scroll to the position of the item in RecyclerView, just like Code A
Is there a way to get the position of a Movice?
Code A
binding.recyclerViewVoice.adapter = myAdapter
mHomeViewModel.listVoiceBySort.observe(this.viewLifecycleOwner) {
myAdapter.submitList(it)
}
//val position=myAdapter.getPostionByItem(aMovice)
//binding.recyclerViewVoice.scrollToPosition(position)
Code B
class VoiceAdapters (private val aHomeViewModel: HomeViewModel, private val mPlay: PlayInterface):
ListAdapter<MVoice, VoiceAdapters.VoiceViewHolder>(MVoiceDiffCallback()) {
private lateinit var mContext: Context
private lateinit var mLifecycleOwner:LifecycleOwner
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): VoiceViewHolder {
mContext = parent.context
mLifecycleOwner = mContext as LifecycleOwner
return VoiceViewHolder(
LayoutVoiceItemBinding.inflate(LayoutInflater.from(parent.context), parent, false).also {
it.lifecycleOwner = mLifecycleOwner
it.aHomeViewModel = aHomeViewModel
}
)
}
override fun onBindViewHolder(holder: VoiceViewHolder, position: Int) {
val inputMVoice = getItem(position)
holder.bind(inputMVoice)
}
inner class VoiceViewHolder (private val binding: LayoutVoiceItemBinding):
RecyclerView.ViewHolder(binding.root) {
fun bind(inputMVoice: MVoice) {
binding.amVoice = inputMVoice
binding.executePendingBindings()
}
}
}
class MVoiceDiffCallback : DiffUtil.ItemCallback<MVoice>() {
override fun areItemsTheSame(oldItem: MVoice, newItem: MVoice): Boolean {
return oldItem.id == newItem.id
}
override fun areContentsTheSame(oldItem: MVoice, newItem: MVoice): Boolean {
return oldItem == newItem
}
}
You can get a reference to the list currently displayed with currentList, and use indexOf() to get the position
fun getPositionByItem(aMovice: MVoice) = currentList.indexOf(aMovice)
Add a ItemClick Listener in fun bind(), then pass the MVoice.getPosition in Toast.
Thus you would able to see the position of item in your toast.
I've done this successfully with a normal ViewAdapter but I can't seem to get it working with a ListAdapter.
Here is my Fragment that does most of the work:
class CrimeListFragment: Fragment() {
//Required interface for hosting activities
interface Callbacks {
fun onCrimeSelected(crimeId: UUID)
}
private var callbacks: Callbacks? = null
private lateinit var crimeRecyclerView: RecyclerView
private val crimeListViewModel: CrimeListViewModel by lazy {
ViewModelProviders.of(this).get(CrimeListViewModel::class.java)
}
override fun onAttach(context: Context) {
super.onAttach(context)
callbacks = context as Callbacks?
}
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
val view = inflater.inflate(R.layout.fragment_crime_list, container, false)
crimeRecyclerView =
view.findViewById(R.id.crime_recycler_view) as RecyclerView
crimeRecyclerView.layoutManager = LinearLayoutManager(context)
crimeRecyclerView.adapter = CrimeListAdapter(emptyList())
return view
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
crimeListViewModel.crimeListLiveData.observe(
viewLifecycleOwner,
Observer { crimes ->
crimes?.let {
Log.i(TAG, "Got crimes ${crimes.size}")
updateUI(crimes)
}
}
)
}
override fun onDetach() {
super.onDetach()
callbacks = null
}
private fun updateUI(crimes: List<Crime>) {
crimeRecyclerView.adapter = CrimeListAdapter(crimes)
}
companion object {
fun newInstance(): CrimeListFragment {
return CrimeListFragment()
}
}
private inner class CrimeHolder(view: View)
: RecyclerView.ViewHolder(view), View.OnClickListener {
private lateinit var crime: Crime
private val titleTextView = itemView.findViewById<TextView>(R.id.crime_title)
private val dateTextView = itemView.findViewById<TextView>(R.id.crime_date)
private val solvedImageView = itemView.findViewById<ImageView>(R.id.crime_solved)
init {
itemView.setOnClickListener(this)
}
fun bind(crime: Crime) {
this.crime = crime
titleTextView.text = crime.title
dateTextView.text = crime.date.toString()
solvedImageView.visibility = if(crime.isSolved) {
View.VISIBLE
} else {
View.GONE
}
}
override fun onClick(v: View) {
callbacks?.onCrimeSelected(crime.id)
}
}
private inner class CrimeListAdapter(var crimes: List<Crime>)
: ListAdapter<Crime, CrimeHolder>(DiffCallback()) {
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): CrimeHolder {
val view =
layoutInflater.inflate(R.layout.list_item_crime, parent, false)
return CrimeHolder(view)
}
override fun onBindViewHolder(holder: CrimeHolder, position: Int) {
holder.bind(crimes[position])
}
}
private inner class DiffCallback: DiffUtil.ItemCallback<Crime>() {
override fun areItemsTheSame(oldItem: Crime, newItem: Crime): Boolean {
return oldItem.id == newItem.id
}
override fun areContentsTheSame(oldItem: Crime, newItem: Crime): Boolean {
return oldItem == newItem
}
}
}
And here is the fragment's viewmodel:
class CrimeListViewModel: ViewModel() {
private val crimeRepository = CrimeRepository.get()
val crimeListLiveData = crimeRepository.getCrimes() //returns LiveData<List<Crime>>
}
Android documentation has this regarding ListAdapter:
While using a LiveData is an easy way to provide data to the adapter, it isn't required - you can use submitList(List) when new lists are available.
I'm supposed to submit a new list instead of creating a new ListAdapter object each time I update the UI. But crimeRecyclerView.adapter has no .submitList() function. So how do I pass on the new list?
LiveData is still new to me so I'm not quite clear on this. I already observe a LiveData stored in my viewmodel. So what do I observe this time? Or do I just add code to my existing Observer?
Finally when I run the code in this state, phone shows an empty RecyclerView. Only UpdateUI() gets called, none of CrimeListAdapter's functions get called. I'm not sure if this is a real problem or just the consequence of the above.
1.I'm supposed to submit a new list instead of creating a new ListAdapter object each time I update the UI. But
crimeRecyclerView.adapter has no .submitList() function. So how do I
pass on the new list?
crimeRecyclerView.adapter return RecyclerView.Adapter type
submitList() is a method of ListAdapter, a sub-class of RecyclerView.Adapter
You need to cast from super to sub class before calling that method, like this.
(crimeRecyclerView.adapter as CrimeListAdapter).submitList(crimes)
2.LiveData is still new to me so I'm not quite clear on this. I already observe a LiveData stored in my viewmodel. So what do I
observe this time? Or do I just add code to my existing Observer?
Your code for this part is good, no need to do more.
3.Finally when I run the code in this state, phone shows an empty RecyclerView. Only UpdateUI() gets called, none of CrimeListAdapter's
functions get called. I'm not sure if this is a real problem or just
the consequence of the above.
The best part of using ListAdapter is you do not need to provide a list of data (crimes in your case) to constructor.
Back to your code, you need to change 3 things.
// crimeRecyclerView.adapter = CrimeListAdapter(emptyList())
crimeRecyclerView.adapter = CrimeListAdapter()
and
// crimeRecyclerView.adapter = CrimeListAdapter(crimes)
(crimeRecyclerView.adapter as CrimeListAdapter).submitList(crimes)
and
//private inner class CrimeListAdapter(var crimes: List<Crime>) :
// ListAdapter<Crime, CrimeHolder>(DiffCallback()) {
//
// override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): CrimeHolder {
// val view = layoutInflater.inflate(R.layout.list_item_crime, parent, false)
// return CrimeHolder(view)
// }
//
// override fun onBindViewHolder(holder: CrimeHolder, position: Int) {
// holder.bind(crimes[position])
// }
//}
private inner class CrimeListAdapter : ListAdapter<Crime, CrimeHolder>(DiffCallback()) {
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): CrimeHolder {
val view = layoutInflater.inflate(R.layout.list_item_crime, parent, false)
return CrimeHolder(view)
}
override fun onBindViewHolder(holder: CrimeHolder, position: Int) {
holder.bind(getItem(position))
}
}