Q: OnClickListener in RecyclerView Adapter not initialized I am trying to add an OnClickListener to a recycler view item i however keep getting this error
lateinit property listener has not been initialized

Here is how my adapter looks like
class CartAdapter(private val cartItems: List<CartItemEntity>? = null) : RecyclerView.Adapter<CartAdapter.CartViewHolder>() {

    private lateinit var listener: OnItemClickListener

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): CartViewHolder {
        val view = LayoutInflater.from(parent.context).inflate(R.layout.cart_item, parent, false)
        return CartViewHolder(view, cartItems!!, listener)
    }

    override fun getItemCount() = cartItems!!.size

    override fun onBindViewHolder(holder: CartViewHolder, position: Int) {
        val cartItem = cartItems?.get(position)
        holder.productPrice.text = cartItem.productPrice.toInt().toString()
        holder.cart = listOf(cartItem)
    }

    class CartViewHolder(val view: View, var cart: List<CartItemEntity>, listener: OnItemClickListener) : RecyclerView.ViewHolder(view) {
        private val cartRemove: TextView = view.findViewById(R.id.cartRemove)

        init {
            cartRemove.setOnClickListener {
                listener.onItemClick(cart)
            }

        }
    }

    interface OnItemClickListener{
        fun onItemClick(cartItems: List<CartItemEntity>?)
    }

    fun setOnItemClickListener(listener: OnItemClickListener){
        this.listener = listener
    }

}

This is how i am implementing it in my Fragment
adapter!!.setOnItemClickListener(object : CartAdapter.OnItemClickListener{
            override fun onItemClick(cartItems: List<CartItemEntity>?) {
                Log.e("Cart Item", ""+ cartItems!![0].id)
            }
        })

Not sure what am doing wrong

A: You can add the listener as part of your CartAdapter constructor 
class CartAdapter(private val cartItems: List<CartItemEntity>? = null, itemListener: OnItemClickListener) : RecyclerView.Adapter<CartAdapter.CartViewHolder>() {

    private val listener: OnItemClickListener = itemListener

    ...

    interface OnItemClickListener{
        fun onItemClick(cartItems: List<CartItemEntity>?)
    }
}

Then from your activity, pass the listener when you initialize the adapter
    val adapter = CartAdapter(itemList, object: CartAdapter.OnItemClickListener {
        override fun onItemClick(cartItems: List<CartItemEntity>?) {
            Log.e("Cart Item", ""+ cartItems!![0].id)
        }
    })


A: create constructor inside your Adapter
  public Adapter(ListenerAdapter click) {
    this.click = click;
}

and send object from fragment when you create recyclerView
private void initRecyclerView(View view) {
    adapter = new Adapter(this);}   

in my case I create View Holder how another class and i have to send listener to ViewHolder too, like below
 @NonNull
@Override
public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
    LayoutInflater inflater = LayoutInflater.from(parent.getContext());
    View view = inflater.inflate(R.layout.item_main_activity, parent, false);
    // we send part of ListenerAdapter to ViewHolder
    return new ViewHolder(view,click);
}

