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DiffUtil Not working in nested recyclerview Kotlin

I have two recycler views. My view is not updated until I used notifyDataSetChanged. I asked for a similar type of issue, but this time I have Github Link. So please have a look and explain to me what I am doing wrong. Thanks
MainActivity.kt
package com.example.diffutilexample
import android.os.Bundle
import android.util.Log
import androidx.activity.viewModels
import androidx.appcompat.app.AppCompatActivity
import com.example.diffutilexample.databinding.ActivityMainBinding
class MainActivity : AppCompatActivity() {
private val viewModel by viewModels<ActivityViewModel>()
private lateinit var binding: ActivityMainBinding
private var groupAdapter: GroupAdapter? = null
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setupViewModel()
binding = ActivityMainBinding.inflate(layoutInflater)
setContentView(binding.root)
viewModel.fetchData()
binding.button.setOnClickListener {
viewModel.addData()
}
}
private fun setupViewModel() {
viewModel.groupListLiveData.observe(this) {
if (groupAdapter == null) {
groupAdapter = GroupAdapter()
binding.recyclerview.adapter = groupAdapter
}
groupAdapter?.submitList(viewModel.groupList?.toMutableList())
binding.recyclerview.post {
groupAdapter?.notifyDataSetChanged()
}
}
}
}
ActivityViewModel.kt
package com.example.diffutilexample
import android.app.Application
import androidx.lifecycle.AndroidViewModel
import androidx.lifecycle.MutableLiveData
import androidx.lifecycle.viewModelScope
import kotlinx.coroutines.launch
class ActivityViewModel(app: Application) : AndroidViewModel(app) {
var groupListLiveData: MutableLiveData<Boolean> = MutableLiveData()
var groupList: ArrayDeque<Group>? = null
set(value) {
field = value
groupListLiveData.postValue(true)
}
var value = 0
fun fetchData() {
viewModelScope.launch {
val response = ApiInterface.create().getResponse()
groupList = groupByData(response.abc)
}
}
private fun groupByData(abc: List<Abc>?): ArrayDeque<Group> {
val result: ArrayDeque<Group> = groupList ?: ArrayDeque()
abc?.iterator()?.forEach { item ->
val key = GroupKey(item.qwe)
result.addFirst(Group(key, mutableListOf(item)))
}
return result
}
fun addData() {
groupList?.let { lastList ->
val qwe = Qwe("Vivek ${value++}", "Modi")
val item = Abc(type = "Type 1", "Adding Message", qwe)
val lastGroup = lastList[0]
lastGroup.list.add(item)
groupList = lastList
}
}
}
Please find the whole code in Github Link. I attached in above

I haven't debugged this, but if you remove your overuse of MutableLists and vars, and simplify your LiveData, you will likely eliminate your bug. At the very least, it will help you track down the problem.
MutableLists and DiffUtil do not play well together!
For example, Group's list should be a read-only List:
data class Group(
val key: GroupKey,
val list: List<Abc?> = emptyList()
)
It's convoluted to have a LiveData that only reports if some other property is usable. Then you're dealing with nullability all over the place here and in the observer, so it becomes hard to tell when some code is going to be skipped or not from a null-safe call. I would change your LiveData to directly publish a read-only List. You can avoid nullable Lists by using emptyList() to also simplify code.
You can avoid publicly showing your interior workings with the ArrayDeque as well. And you are lazy loading the ArrayDeque unnecessarily, which leads to having to deal with nullability unnecessarily.
class ActivityViewModel(app: Application) : AndroidViewModel(app) {
private val _groupList = MutableLiveData<List<Group>>()
val groupList: LiveData<List<Group>> get() = _groupList
private val trackedGroups = ArrayDeque<Group>()
private var counter = 0
fun fetchData() {
viewModelScope.launch {
val response = ApiInterface.create().getResponse()
addFetchedData(response.abc.orEmpty())
_groupList.value = trackedGroups.toList() // new copy for observers
}
}
private fun addFetchedData(abcList: List<Abc>) {
for (item in abcList) {
val key = GroupKey(item.qwe)
trackedGroups.addFirst(Group(key, listOf(item)))
}
}
fun addData() {
if (trackedGroups.isEmpty())
return // Might want to create a default instead of doing nothing?
val qwe = Qwe("Vivek ${counter++}", "Modi")
val item = Abc(type = "Type 1", "Adding Message", qwe)
val group = trackedGroups[0]
trackedGroups[0] = group.copy(list = group.list + item)
_groupList.value = trackedGroups.toList() // new copy for observers
}
}
In your Activity, since your GroupAdapter has no dependencies, you can instantiate it at the call site to avoid dealing with lazy loading it. And you can set it to the RecyclerView in onCreate() immediately.
Because of the changes in ViewModel, observing becomes very simple.
If you do something in setupViewModel() that updates a view immediately, you'll have a crash, so you should move it after calling setContentView().
class MainActivity : AppCompatActivity() {
private val viewModel by viewModels<ActivityViewModel>()
private lateinit var binding: ActivityMainBinding
private val groupAdapter = GroupAdapter()
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
binding = ActivityMainBinding.inflate(layoutInflater).apply {
setContentView(root)
recyclerview.adapter = groupAdapter
button.setOnClickListener {
viewModel.addData()
}
}
setupViewModel()
viewModel.fetchData()
}
private fun setupViewModel() {
viewModel.groupList.observe(this) {
groupAdapter.submitList(it)
}
}
}
Your DiffUtil.ItemCallback.areItemsTheSame in GroupAdapter is incorrect. You are only supposed to check if they represent the same item, not if their contents are the same, so it should not be comparing lists.
override fun areItemsTheSame(oldItem: Group, newItem: Group): Boolean {
return oldItem.key == newItem.key
}
And in GroupViewHolder, you are creating a new adapter for the inner RecyclerView every time it is rebound. That defeats the purpose of using RecyclerView at all. You should only create the adapter once.
I am predicting that the change in the nested list is going to look weird when the view is being recycled rather than just updated, because it will animate the change from what was in the view previously, which could be from a different item. So we should probably track the old item key and avoid the animation if the new key doesn't match. I think this can be done in the submitList() callback parameter to run after the list contents have been updated in the adapter by calling notifyDataSetChanged(), but I haven't tested it.
class GroupViewHolder(val binding: ItemLayoutBinding) : RecyclerView.ViewHolder(binding.root) {
companion object {
//...
}
private val adapter = NestedGroupAdapter().also {
binding.nestedRecyclerview.adapter = it
}
private var previousKey: GroupKey? = null
fun bindItem(item: Group?) {
val skipAnimation = item?.key != previousKey
previousKey = item?.key
adapter.submitList(item?.list.orEmpty()) {
if (skipAnimation) adapter.notifyDataSetChanged()
}
}
}
Side note: your adapters' bindView functions are confusingly named. I would just make those into secondary constructors and you can make the primary constructor private.
class GroupViewHolder private constructor(private val binding: ItemLayoutBinding) :
RecyclerView.ViewHolder(binding.root) {
constructor(parent: ViewGroup) : this(
ItemLayoutBinding.inflate(
LayoutInflater.from(parent.context),
parent,
false
)
)
//...
}

I'm not entirely sure, and I admit I haven't extensively studied your code, and this is not a solution, but this might point you in the right direction of how to solve it.
The thing about
groupAdapter?.submitList(viewModel.groupList?.toMutableList())
Is that toMutableList() does indeed make a copy of the list. But each of the objects in the list are not copies. If you add things to an object in the original list, like you do in addData() it in fact is also already added to the copy that is in the adapter. That's why a new submitList doesn't recognize it as a change because it is actually the same as it was before the submitList.
As far as I understand, working with DiffUtil works best if the list you submit only contains objects that are immutable, so mistakes like this can't happen. I have ran into a similar problem before and the solution is also not straightforward. In fact, I don't entirely remember how I solved it back then, but hopefully this pushes you in the right direction.

I can't use toDouble() method with Kotlin

I am new to kotlin and I am trying an execise.
I want to calculate the tip as % of the cost of the service.I enter my cost of service in an EditText... so far so good.
now I want to convert this the value I entered to double, which the datatype I need for my calculation.
this is my code:
package com.example.tiptime2
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import com.example.tiptime2.databinding.ActivityMainBinding
class MainActivity : AppCompatActivity() {
lateinit var binding: ActivityMainBinding
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
binding = ActivityMainBinding.inflate(layoutInflater)
setContentView(binding.root)
binding.calculate.setOnClickListener { calculateTip() }
}
fun calculateTip(){
val myTextString= binding.costOfService.text.toString()
val myCost = myTextString.toString()
val cost = myCost.toDouble()
}
}
androidStudio doesn't recognize toDouble()
why??

You're casting to .toString() twice and you need to update the data-binding. Roughly alike:
val cost = Double.parseDouble(binding.costOfService.text.toString())
// some calculations
binding.costOfService.setText(String.valueOf(cost))
Instead of handling single values, it's common to bind a view-model, which has all of them.

I suggest you explicit define variables type for debugging
fun calculateTip() {
val costText: String = binding.costOfService.text.toString()
val cost: Double = costText.toDouble()
}
Still your code looks valid!

How to build a live data based on lateinit property?

I have a property with late initialization.
Now I want to provide a live data which does not emit anything until the property is initialized completely.
How to do this in proper Kotlin way?
class SomeConnection {
val data: Flow<SomeData>
...
class MyViewModel {
private lateinit var _connection: SomeConnection
// private val _connection: CompletableDeferred<SomeConnection>()
val data = _coonection.ensureInitilized().data.toLiveData()
fun connect(){
viewModelScope.launch {
val conn = establishConnection()
// Here I have to do something for the call ensureInitilized to proceed
}
}
private suspend fun establishConnection(){
...
}

Declare a MutableLiveData emitting values of type SomeConnection and a corresponding LiveData.
private val _connectionLiveData = MutableLiveData<SomeConnection>()
val connectionLiveData: LiveData<SomeConnection> = _connectionLiveData
Then assign value to _connectionLiveData when _connection is initialized:
if (::_connection.isInitialized()) _connectionLiveData.value = _connection
(or _connectionLiveData.postValue(_connection) if your code works concurrently)
Now observe this LiveData in another place in code, I'll use fragment here for the sake of example:
override fun firstOnViewCreated(view: View, savedInstanceState: Bundle?) {
viewModel.connectionLiveData.observe(this, ::sendData)
}
Then send the desired data via the corresponding view model method

Failed getStringExtra Kotlin mvvm

I want to move from one Activity which displays a RecyclerView to another Activity (detail). But when I added data transmission via Intent, the data always failed to be taken in the Activity detail.
This is the error:
My MainDetail:
private lateinit var viewModel: MainDetailModel
var idAnime: String = "34134"
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main_detail)
idAnime = intent.getStringExtra("idAnime")
println("idanime $idAnime")
setupFragment()
setupViewModel()
}
}
ViewModel:
class MainViewModel(context: Application, private val appRepository: AppRepository, private val contexts: Context) : AndroidViewModel(context), MainItemClickAction {
override fun onItemClicked(detailModel: DetailModel) {
var intent = Intent(contexts, MainDetailActivity::class.java)
intent.putExtra("idAnime",detailModel.mal_id )
contexts.startActivity(intent)
}
}

Check if your field "detailModel.mal_id" mal_id in that case is string, because you're requesting string in details activity. If it's string check also if this "mal_id" is null. Other issues from code you provided can't be seen.

Check your value idAnime, it exists or not, I think is better check all value is empty or not before putting into listView or another view.

Receiving data in incorrect order on Querying database

Activity receiving intent
class AddNoteActivity : AppCompatActivity() {
private lateinit var addViewModel: NoteViewModel
private lateinit var titleEditText: TextInputEditText
private lateinit var contentEditText: TextInputEditText
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_add_note_activty)
setSupportActionBar(toolbar)
addViewModel = ViewModelProviders.of(this).get(NoteViewModel::class.java)
titleEditText = findViewById(R.id.itemTitle)
contentEditText = findViewById(R.id.itemNote)
val extra = intent.extras
if (extra != null) {
val uuid = extra.getLong("UUID")
val note: Notes? = addViewModel.getNote(uuid)
titleEditText.setText(note!!.title)
contentEditText.setText(note.note)
}
}
}
NoteViewModel class
class NoteViewModel(application: Application) : AndroidViewModel(application) {
companion object {
private var note: Notes = Notes(0, "", "test title", "test ontent")
}
fun getNote(uuid: Long?): Notes {
val job = async(CommonPool) {
getNoteAsyncTask(notesDatabase).execute(uuid)
}
runBlocking { job.await() }
return note
}
class getNoteAsyncTask(database: NotesDatabase) : AsyncTask<Long, Unit, Unit>() {
private val db: NotesDatabase = database
override fun doInBackground(vararg params: Long?) {
note = db.notesDataDao().getNote(params[0])
}
}
}
If I pass an intent to get a Note object from the database with a uuid and set that received data in titleEditText and contentEditText, the data set in the Note was from previous intent invoked when we clicked on the Note item in RecyclerView. On clicking the Note item for the first time, I get the default value which I have set "test title" and "test content".
Aforementioned is the behavior most of the time. Sometimes the data set in titleEditText and contentEditText is of the correct Note object.
Can someone please tell me what I have done wrong? How can I correct my apps behavior?

Unfortunately, there is a big mistake in how you use a view model to provide a data to your view(AddNoteActivity).
Basically, your view never has a chance to wait for the data to be fetched as it always receives a default value. This happens because the AsyncTask runs on its own thread pool so the coroutine completes immediately and returns a default value.
You should consider using LiveData to post a new object to your view and refactor your view model.
So, you need to make a query to the database synchronous and observe changes to a note rather than have a getter for it. Of course, in a real life scenario it might be a good idea to have different kind of states to be able to show a spinner while a user is waiting. But this is another big question. So to keep things simple consider changing your view model to something like that:
class NoteViewModel(private val database: NotesDatabase) : ViewModel { // you do not need an application class here
private val _notes = MutableLiveData<Notes>()
val notes: LiveData<Notes> = _notes
fun loadNotes(uuid: Long) {
launch(CommonPool) {
val notes = database.notesDataDao().getNote(uuid)
_notes.setValue(notes)
}
}
}
Then, you can observe changes to the note field in your activity.
class AddNoteActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
// ...
val noteViewModel = ViewModelProviders.of(this).get(NoteViewModel::class.java)
noteViewModel.notes.observe(this, Observer {
title.text = it.title
content.text = it.note
})
}
}
Also you need to use a ViewModelProvider.Factory to create your view model and properly inject dependencies into it. Try to avoid having a context there as it makes it much harder to test.