Load More (Pagination) ListAdapter and RecyclerView

LoadMore.Kt

/**
* Use these classes to implement pagination without paging libs
*/ 

import android.annotation.SuppressLint
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.recyclerview.widget.DiffUtil
import androidx.recyclerview.widget.ListAdapter
import androidx.recyclerview.widget.RecyclerView
import androidx.viewbinding.ViewBinding
import android.content.Context
import android.util.AttributeSet

class LoadMoreRecyclerView @JvmOverloads constructor(
    context: Context, attrs: AttributeSet? = null, defStyleAttr: Int = 0
) : RecyclerView(context, attrs, defStyleAttr) {

    fun setupLoadMoreWithViewModel(vm: LoadMoreVM<*>) {
        setupLoadMore(
            predicate = vm.canLoadMore(),
            onLoadMore = { vm.loadMore() })
    }

}

abstract class LoadMoreListAdapter<T, VB : ViewBinding>(diffCallBack: DiffUtil.ItemCallback<T>) :
    ListAdapter<T, RecyclerView.ViewHolder>(diffCallBack) {

    override fun getItemViewType(position: Int): Int {
        return when (getItem(position)) {
            null -> ITEM_VIEW_TYPE_LOADING
            else -> ITEM_VIEW_TYPE
        }
    }

    inner class ItemViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView)

    inner class LoadingViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView)

    abstract fun getItemView(inflater: LayoutInflater, parent: ViewGroup) : View

    abstract fun getLoaderView(inflater: LayoutInflater, parent: ViewGroup) : View

    abstract fun getViewBinding(itemView: View): VB

    abstract fun bindItemView(binding: VB, item: T, holder: RecyclerView.ViewHolder)

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder {
        val inflater = LayoutInflater.from(parent.context)
        return when (viewType) {
            ITEM_VIEW_TYPE -> ItemViewHolder(getItemView(inflater, parent))
            else -> LoadingViewHolder(getLoaderView(inflater, parent))
        }
    }

    override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
        if (holder.itemViewType == ITEM_VIEW_TYPE)
            bindItemView(getViewBinding(holder.itemView), getItem(position), holder)
    }

    @SuppressLint("NotifyDataSetChanged")
    fun addChangedList(notificationList: List<T>?) {
        removeLoadingView()
        submitList(notificationList)
        notifyDataSetChanged()
    }

    fun clearOldListAndAddNew(list: List<T>) {
        removeLoadingView()
        submitList(null)
        submitList(list)
    }

    private fun removeLoadingView() {
        if (currentList.isNotEmpty() && getItem(currentList.size - 1) == null) {
            val listWithOutLoading = ArrayList(currentList).apply { removeAt(currentList.size - 1) }
            submitList(listWithOutLoading)
        }
    }

    private fun addLoadingView() {
        if ((currentList.size - 1) != -1 && getItem(currentList.size - 1) != null) {
            submitList(currentList + null)
            notifyItemInserted(currentList.size)
        }
    }

    companion object {
        private const val ITEM_VIEW_TYPE = 0
        private const val ITEM_VIEW_TYPE_LOADING = 1

        fun LoadMoreRecyclerView.setupLoadMore(predicate : Boolean, onLoadMore : () -> Unit) {
            addOnScrollListener(object : RecyclerView.OnScrollListener() {
                override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) {
                    super.onScrolled(recyclerView, dx, dy)
                    if (!recyclerView.canScrollVertically(1) && predicate) {
                        onLoadMore()
                        if (adapter is LoadMoreListAdapter<*, *>)
                            (adapter as LoadMoreListAdapter<*, *>).addLoadingView()
                    }
                }
            })
        }
    }
}