SectionAdapter

SectionAdapter.kt

import android.view.ViewGroup
import androidx.recyclerview.widget.RecyclerView

abstract class SectionAdapter : RecyclerView.Adapter<RecyclerView.ViewHolder>() {

    private val headerPositions: MutableMap<Int, Int> = mutableMapOf()
    private val itemPositions: MutableMap<Int, Int> = mutableMapOf()
    private val sectionItemPositions: MutableMap<Int, Int> = mutableMapOf()
    private var listSize = 0
    private var headerSize = 0

    override fun onCreateViewHolder(parent: ViewGroup, type: Int): RecyclerView.ViewHolder {
        if (type == 0) {
            return onCreateSectionViewHolder(parent)
        }
        return onCreateItemViewHolder(parent)
    }

    override fun onBindViewHolder(viewHolder: RecyclerView.ViewHolder, position: Int) {
        if (headerPositions.contains(position)) {
            //section
            onBindSectionViewHolder(viewHolder, headerPositions[position] ?: 0)
        }
        val currentSection = sectionItemPositions[position]
        val currentSectionPosition = itemPositions[position]
        if (currentSection != null && currentSectionPosition != null) {
            onBindItemViewHolder(viewHolder, currentSection, currentSectionPosition)
        }
    }

    override fun getItemViewType(position: Int): Int {
        if (headerPositions.contains(position)) {
            //section
            return 0
        }
        return 1
    }

    override fun getItemCount(): Int {
        var size = 0
        if(listSize != 0)
            return listSize
        for (sectionIndex in 0 until sectionCount()) {
            if(!headerPositions.contains(size)) {
                headerPositions[size] = headerSize
                headerSize++
                size++
                for (itemIndex in 0 until itemCount(sectionIndex)) {
                    sectionItemPositions[size] = sectionIndex
                    itemPositions[size] = itemIndex
                    size++
                }
            }
        }
        listSize = size
        return size
    }

    abstract fun sectionCount(): Int
    abstract fun itemCount(section: Int): Int
    abstract fun onCreateSectionViewHolder(viewGroup: ViewGroup): RecyclerView.ViewHolder
    abstract fun onCreateItemViewHolder(viewGroup: ViewGroup): RecyclerView.ViewHolder
    abstract fun onBindSectionViewHolder(viewHolder: RecyclerView.ViewHolder, sectionPosition: Int)
    abstract fun onBindItemViewHolder(viewHolder: RecyclerView.ViewHolder, sectionPosition: Int, itemPosition: Int)
}