DiffUtil not updating ListAdapter after updating ArrayList contents

Question

I am trying to update ArrayList which is inside in MutableLiveData. whenever I change the content in ArrayList, ListAdapter is not updating.

ViewModel

private var _tileNumberList:MutableLiveData<ArrayList<TileNumber>> = MutableLiveData()

var tempTileNumberList: ArrayList<TileNumber> = ArrayList()

val tileNumberList:LiveData<ArrayList<TileNumber>>
get() = _tileNumberList

init {
    for (i in 1..9){
        for (j in 1..9){
            //tileNumberList.add(TileNumber(0,i,j))
            tempTileNumberList.add(TileNumber(0,i,j))
        }
    }

 fun onStart() {

        tempTileNumberList[count].number = 8
        _tileNumberList.value = tempTileNumberList
        count++

    }

whenever I call onStart method list values changes but ListAdapter not updating with latest values

MainActivity

backTrackingViewModel.tileNumberList.observe(this, Observer {
               it?.let {
                   //adapter.submitList(null)
                   adapter.submitList( it)
               }
            Toast.makeText(
                applicationContext,
                "Hey",
                Toast.LENGTH_SHORT
            ).show()
        })

when i set adapter.submitList(null) then my ListAdapter is updating

TileNumber

data class TileNumber(var number:Int,val row:Int,val column:Int) {
}

I tried this link references but didn't work

ListAdapter not updating item in RecyclerView

https://stackoverflow.com/a/50062174/6925888 (this is not a good solution)

DiffUtil ItemCallback areContentsTheSame() always returns true after updating an item on the ListAdapter

According to the linked question "So if you pass the same list to the adapter it does not even call the DiffUtil". Did you check that? — sanjeev, Feb 10 '20 at 08:50
@Mike yes mike I am getting toast every time when I press onStart. — iamkdblue, Feb 10 '20 at 09:22

score 0 · Answer 1 · answered Feb 10 '20 at 08:36

0

I think you should initialize tileNumberList list like this

var tileNumberList: LiveData<ArrayList<TileNumber>> =  _tileNumberList

And then observe it in MainActivity just like you're doing it

answered Feb 10 '20 at 08:36

qki

1,769
11
25

This doesn't make sense – Zun Feb 10 '20 at 08:44
Why not? changing value of `_tileNumberList` will trigger `tileNumberList` which we are observing in Fragment – qki Feb 10 '20 at 08:49

score 0 · Answer 2 · answered Feb 10 '20 at 10:49

0

I have two possible options why this code doesn't work:

Items are changed in place - i.e. you change the items inside the list. Since the list is passed to adapter, the adapter's list is changed as well. Solution:

_tileNumberList.value = tempTileNumberList.toList()
You haven't overridden equals() and hashCode() for TileNumber class.

answered Feb 10 '20 at 10:49

Mike

2,547
3
16
30

Thanks, Mike, let the correct item position is not going to change but only content going to change. (on the same position of list), I tried this but no luck. – iamkdblue Feb 10 '20 at 10:55
You should also try setting item directly: tempTileNumberList[count] = TileNumber(number = 8) – Mike Feb 10 '20 at 11:15

score 0 · Answer 3 · edited Mar 14 '21 at 14:27

0

According to ListAdapter.SubmitList() documentation, until you pass the list with the same reference you will never update your list. To make it work you can simply invoke:

adapter.submitList(it.toList())

edited Mar 14 '21 at 14:27

Tomerikoo

18,379
16
47
61

answered Mar 14 '21 at 06:30

random.123

65
8

score 0 · Answer 4 · answered May 08 '21 at 03:09

Replace this:

 fun onStart() {

        tempTileNumberList[count].number = 8
        _tileNumberList.value = tempTileNumberList
        count++

    }

with this:

 fun onStart() {

        val tileNumber = tempTileNumberList[count].copy()  
        tileNumber.number = 8 
        tempTileNumberList.set(count, tileNumber)  
        _tileNumberList.value = tempTileNumberList
        count++

    }

Here I am using Kotlin data class copy() method.

DiffUtil not updating ListAdapter after updating ArrayList contents

4 Answers4