kotlin.TypeCastException: null cannot be cast to non-null type kotlin.collections.MutableList

Question

please dont marked as duplicate , as the question is slightly different ---> null cannot be cast to non-null type kotlin.collections.MutableList

Answer 1

Looks like it can be fixed by changing few lines:

Make CartAdapter accept nullable argument dataList, since your api request may return null and passing it would cause NPE.

class CartAdapter(context: Context, dataList: MutableList<DataCart?>?)

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Since our dataList is nullable and calling dataList.size might throw NPE we need to make safe call using ?. And if it's null we just return 0, telling recyclerView that there are 0 items.

override fun getItemCount() = datalist?.size ?: 0

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Need to make val retro:List<DataCart> nullable, because response.body()?.data may return null. We just convert retro to mutableList using extension function toMutableList(), with safe call operator "?". If retro is null then null value will be passed to CartAdapter, and since our adapter handles null value it will proceed without errors

if (response.isSuccessful) {
                val retro:List<DataCart>? = response.body()?.data
                totalamount.setText(response.body()?.total.toString())
                generateDataList(retro?.toMutableList())
            }

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Remove init() function from CartAdapter and add var(actually should be val) before arguments in constructor. init() is redundant here because u r using it to assign values to redundant, duplicate member variables. By adding var(should be val) to constructor arguments they will be assigned values and be available as member variables, right after object construction.

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Since dataList is nullable, and we need to determine its size for further logic safe call needs to be used, and if its null return true - empty

 (dataList?.isEmpty() ?: true)

or use

`(dataList.isNullOrEmpty())` 

which is cleaner, and should work too.

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NOTE: Personally, i would'nt suggest you to retinitialize Adapter everytime you need to change values. Instead create val items = arrayListOf<DataCart>(). as a member variable and add a setter function for updating it, inside of which you would call notifyDatasetChanged() or other notify methods.

Answer 2

Can't find a reason to use MutableList but your issue is incorrect type cast (dataList as MutableList<DataCart>). This is cause null cannot be cast to non-null type. You can simplify code using class CartAdapter(private val context: Context, private val dataList: ArrayList<DataCart?>?) and remove var dataList: MutableList<DataCart?>, private val context: Context and init{}

Answer 3

Null check by using the Elvis operator in the part to set in the shopping cart

The first or second method seems to be good