viewHolder3.kt

class LayoutManager(private val recycler: Recycler) {
    fun getViewForPosition(pos: Int): View {
        return recycler.getView(pos)
    }
}

class Recycler(
    private val adapter: Adapter,
    private val recyclerPool: RecyclerPool,
    private val viewCache: ViewCache
) {
    fun getView(pos: Int): View {
        val viewOrNull = viewCache.getOrNull(pos)
        // view found then return view
        if (viewOrNull != null) {
            return viewOrNull
        }
        val viewType = adapter.getViewType(pos)
        val holderOrNull = recyclerPool.getViewHolderByType(viewType)
        // view holder found -> bind and return view
        if (holderOrNull != null) {
            adapter.bindViewHolder(holderOrNull,pos)
            return holderOrNull.itemView
        }
        // create viewholder and bind viewholder and return view
        val holder = adapter.createViewHolder(viewType)
        adapter.bindViewHolder(holder,pos)
        return holder.itemView
    }
}

class ViewCache {
    private val viewCache = mutableMapOf<Int, View>()
    fun getOrNull(pos: Int): View? = viewCache.get(pos)
    fun put(pos: Int, view: View) {
        viewCache.put(pos, view)
    }
}

abstract class Adapter {
    abstract fun getViewType(pos: Int): ViewType
    abstract fun bindViewHolder(holder: ViewHolder,pos:Int)
    abstract fun createViewHolder(viewType: ViewType): ViewHolder
}