问题
please dont marked as duplicate , as the question is slightly different ---> null cannot be cast to non-null type kotlin.collections.MutableList
Scenerios:-
i have been performing delete cart using retrofit..
- if atleast one item is present ,it displays in recyclerview
2.if cart is empty ,it crashes with a above error
here is my adapter code:-
class CartAdapter(context: Context, dataList: MutableList<DataCart?>) :
RecyclerSwipeAdapter<CartAdapter.CustomViewHolder>() { //added RecyclerSwipeAdapter and override
private var dataList: MutableList<DataCart>
private val context: Context
lateinit var dialog:ProgressDialog
var progressDialog: ProgressDialog? = null
inner class CustomViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
val mView: View
val swipelayout:SwipeLayout
val productiamge: ImageView
val productname: TextView
val productcategory: TextView
val productprice: TextView
val quantity:TextView
val tvDelete:TextView
init {
mView = itemView
productiamge= mView.findViewById(R.id.imagecart)
productname= mView.findViewById(R.id.imagenamecart)
productcategory= mView.findViewById(R.id.imagecategory)
productprice =mView.findViewById(R.id.price)
quantity=mView.findViewById(R.id.quantity)
swipelayout=mView.findViewById(R.id.swipe)
tvDelete=mView.findViewById(R.id.tvDelete)
}
}
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): CustomViewHolder {
val layoutInflater = LayoutInflater.from(parent.context)
val view: View = layoutInflater.inflate(R.layout.addtocart_item, parent, false)
return CustomViewHolder(view)
}
override fun getSwipeLayoutResourceId(position: Int): Int {
return R.id.swipe;
}
override fun onBindViewHolder(holder: CustomViewHolder, position: Int) {
val progressDialog :ProgressDialog= ProgressDialog(context);
holder.productname.text = dataList.get(position).product.name ?: null
holder.productcategory.text = "(" +dataList.get(position).product.product_category +")"
holder.productprice.text = dataList.get(position).product.cost.toString()
Glide.with(context).load(dataList.get(position).product.product_images)
.into(holder.productiamge)
holder.quantity.text=dataList.get(position).quantity.toString()
holder.swipelayout.setShowMode(SwipeLayout.ShowMode.PullOut)
Log.e("checkidd",dataList.get(position).product.id.toString())
// Drag From Right
// Drag From Right
holder.swipelayout.addDrag(
SwipeLayout.DragEdge.Right,
holder.swipelayout.findViewById(R.id.bottom_wrapper)
)
val id =dataList.get(position).product?.id
holder.swipelayout.addSwipeListener(object : SwipeListener {
override fun onClose(layout: SwipeLayout) { }
override fun onUpdate(layout: SwipeLayout, leftOffset: Int, topOffset: Int) {
//you are swiping.
}
override fun onStartOpen(layout: SwipeLayout) {}
override fun onOpen(layout: SwipeLayout) {
}
override fun onStartClose(layout: SwipeLayout) {}
override fun onHandRelease(
layout: SwipeLayout,
xvel: Float,
yvel: Float
) {
}
})
holder.swipelayout.getSurfaceView()
.setOnClickListener(View.OnClickListener {
})
holder.tvDelete.setOnClickListener(View.OnClickListener {
view ->
val token :String = SharedPrefManager.getInstance(context).user.access_token.toString()
RetrofitClient.instancecart.deletecart(token,id!!)
.enqueue(object : Callback<DeleteResponse> {
override fun onFailure(call: Call<DeleteResponse>, t: Throwable) {
}
override fun onResponse(
call: Call<DeleteResponse>,
response: Response<DeleteResponse>
) {
var res = response
if (res.body()?.status==200) {
Toast.makeText(
context,
res.body()?.message,
Toast.LENGTH_LONG
).show()
progress()
mItemManger.removeShownLayouts(holder.swipelayout)
notifyItemChanged(position)
notifyItemRemoved(position)
dataList?.removeAt(position)
notifyItemRangeChanged(position, dataList?.size!!)
mItemManger.closeAllItems()
progressDialog.show()
}
else{
try {
val jObjError =
JSONObject(response.errorBody()!!.string())
Toast.makeText(
context,
jObjError.getString("message")+jObjError.getString("user_msg"),
Toast.LENGTH_LONG
).show()
} catch (e: Exception) {
Toast.makeText(context, e.message, Toast.LENGTH_LONG).show()
Log.e("errorrr",e.message)
}
}
}
})
mItemManger.bindView(holder.itemView, position)
})
}
override fun getItemCount(): Int {
return dataList.size
}
fun progress()
{
progressDialog?.dismiss()
val intent =
Intent(context.applicationContext, AddToCart::class.java)
intent.flags =
Intent.FLAG_ACTIVITY_NEW_TASK or Intent.FLAG_ACTIVITY_MULTIPLE_TASK
context.applicationContext.startActivity(intent)
}
init {
this.context = context
this.dataList = dataList
}}
here is my activity:
class AddToCart:AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.add_to_cart)
val totalamount:TextView=findViewById(R.id.totalamount)
val token: String =
SharedPrefManager.getInstance(
applicationContext
).user.access_token.toString()
RetrofitClient.instancecart.listcart(token).enqueue( object :
Callback<CartResponse> {
override fun onFailure(call: Call<CartResponse>, t: Throwable) {
Toast.makeText(applicationContext,"falied", Toast.LENGTH_LONG).show()
}
override fun onResponse(
call: Call<CartResponse>,
response: Response<CartResponse>
) {
val res=response
if (response.isSuccessful) {
val retro:List<DataCart> = response.body()!!.data
totalamount.setText(response.body()?.total.toString())
generateDataList(retro as MutableList<DataCart?>)
}
}
})
}
fun generateDataList( dataList:MutableList<DataCart?>) {
val recyclerView=findViewById<RecyclerView>(R.id.addtocartrecyleview) as? RecyclerView
val linear:LinearLayoutManager=
LinearLayoutManager(applicationContext,LinearLayoutManager.VERTICAL, false)
recyclerView?.layoutManager=linear
val adapter = CartAdapter(this@AddToCart,dataList)
recyclerView?.adapter=adapter
recyclerView?.addItemDecoration
(DividerItemDecorator(resources.getDrawable(R.drawable.divider)))
recyclerView?.setHasFixedSize(true)
adapter.notifyDataSetChanged()
if (dataList.isEmpty()) {
recyclerView?.setVisibility(View.GONE)
textviewempty.setVisibility(View.VISIBLE)
} else {
recyclerView?.setVisibility(View.VISIBLE)
textviewempty.setVisibility(View.GONE)
}
recyclerView?.addOnScrollListener(object :
RecyclerView.OnScrollListener() {
override fun onScrollStateChanged(recyclerView: RecyclerView, newState: Int) {
super.onScrollStateChanged(recyclerView, newState)
Log.e("RecyclerView", "onScrollStateChanged")
}
override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) {
super.onScrolled(recyclerView, dx, dy)
}
})
}
override fun onBackPressed() {
super.onBackPressed()
val intent = Intent(this, HomeActivity::class.java)
startActivityForResult(intent, 2)
}
}
i tried this-->by doing some changes-->
1--> var dataList: MutableList<DataCart?>
2--> var dataList: MutableList<>?=null
3--> var dataList: MutableList<>
Error log after doing Mutablelist to Arraylist
kotlin.TypeCastException: null cannot be cast to non-null type java.util.ArrayList<com.example.store.Cart.DataCart>
at com.example.store.Cart.AddToCart$onCreate$1.onResponse(AddToCart.kt:40)
at retrofit2.ExecutorCallAdapterFactory$ExecutorCallbackCall$1$1.run(ExecutorCallAdapterFactory.java:70)
at android.os.Handler.handleCallback(Handler.java:873)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:224)
at android.app.ActivityThread.main(ActivityThread.java:7147)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:536)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:876)
but nothing seems to be handling null
Please help me
回答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?>?)
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
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())
}
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.
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.
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.
回答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{}
回答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
来源：https://stackoverflow.com/questions/63224711/kotlin-typecastexception-null-cannot-be-cast-to-non-null-type-kotlin-collection