In my application I want used RecyclerView and I want when click on Items, change background.
I want first show default item for selected and when user change this default item, change background and deselected this default item.

My Code :

class StateAdapter constructor() : RecyclerView.Adapter<StateAdapter.ViewHolder>() {

    private lateinit var binding: ItemSimpleTxtBinding
    private lateinit var context: Context
    private var moviesList = emptyList<StateTypes>()
    private var selectedItem = -1

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
        binding = ItemSimpleTxtBinding.inflate(LayoutInflater.from(parent.context), parent, false)
        context = parent.context
        return ViewHolder()
    }

    override fun onBindViewHolder(holder: ViewHolder, position: Int) {
        //getItem from PagingDataAdapter
        holder.bind(moviesList[position], position)
        //Not duplicate items
        holder.setIsRecyclable(false)
    }

    override fun getItemCount() = moviesList.size

    inner class ViewHolder : RecyclerView.ViewHolder(binding.root) {

        @SuppressLint("SetTextI18n")
        fun bind(item: StateTypes, position: Int) {
            binding.apply {
                itemTxt.text = item.name
                //Click
                binding.itemCard.setOnClickListener {
                    selectedItem = adapterPosition
                    notifyDataSetChanged()
                    onItemClickListener?.let {
                        it(position)
                    }
                }
                //Change color
                if (selectedItem == adapterPosition) {
                    binding.itemCard.setCardBackgroundColor(ContextCompat.getColor(context, R.color.meatBrown))
                } else {
                    binding.itemCard.setCardBackgroundColor(ContextCompat.getColor(context, R.color.white))
                }
                //Default
                selectedItem = 1
            }
        }
    }

    private var onItemClickListener: ((Int) -> Unit)? = null

    fun setOnItemClickListener(listener: (Int) -> Unit) {
        onItemClickListener = listener
    }

    fun setData(data: List<StateTypes>) {
        val moviesDiffUtil = NotesDiffUtils(moviesList, data)
        val diffUtils = DiffUtil.calculateDiff(moviesDiffUtil)
        moviesList = data
        diffUtils.dispatchUpdatesTo(this)
    }

    class NotesDiffUtils(private val oldItem: List<StateTypes>, private val newItem: List<StateTypes>) :
        DiffUtil.Callback() {

        override fun getOldListSize(): Int {
            return oldItem.size
        }

        override fun getNewListSize(): Int {
            return newItem.size
        }

        override fun areItemsTheSame(oldItemPosition: Int, newItemPosition: Int): Boolean {
            return oldItem[oldItemPosition] === newItem[newItemPosition]
        }

        override fun areContentsTheSame(oldItemPosition: Int, newItemPosition: Int): Boolean {
            return oldItem[oldItemPosition] === newItem[newItemPosition]
        }
    }
}

For set default item I added this code :

//Default
selectedItem = 1

But after added this line, when click on Item not change any items background!
When removed default item change items background successfully!
How can I fix it?

CodePudding user response：

You are setting selectedItem = 1 in every cell of the recyclerview. Set selectedItem = 1 once as global variable instead of -1 like this:

 private var selectedItem = 1