adapter.kt

class MyAdapter(private val dataset: List<String>)
    : RecyclerView.Adapter<MyAdapter.ViewHolder>() {

    private var currentSelection = 0

    /**
     * The view holder.
     */
    class ViewHolder(val view: View) : RecyclerView.ViewHolder(view) {


        lateinit var myTextView : TextView

        /**
         * Method that binds the data to the view.
         */
        fun bindElementsToView(position: Int, selected: Boolean,
                               function: (Int) -> Unit ,
                               textToShow : String) {
            myTextView = view.findViewById(R.id.content_text)
            myTextView.text = textToShow
            // Setting the state of the view so that the style defined in selector can be applied to it.
            view.isSelected = selected
            //on click the function is invoked and the currentSelection is updated.
            view.setOnClickListener {
                function(position)
            }
        }
    }

   
    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int):
            ViewHolder {
        val view = LayoutInflater.from(parent.context)
                .inflate(R.layout.food_portion_list_item, parent, false)
        return ViewHolder(view)
    }

    override fun getItemCount() = dataset.size


    /**
    * Binding the data into the view holder.
    **/
    override fun onBindViewHolder(holder: ViewHolder, position: Int) {
        /**
        * This function is used to update the class variable with the current selected index and update the recycler view.
        **/
        val function = { pos: Int ->
           if (currentSelection != pos) {
                currentSelection = pos
                notifyDataSetChanged()
             }
        }
        holder.bindElementsToView(position, position == currentSelection, function , dataset[position])
    }


}