HeaderAdapter.kt

package jp.dip.sys1.aozora.views.adapters

import android.support.v7.widget.RecyclerView
import android.view.ViewGroup
import java.util.*

abstract class HeaderAdapter<ViewHolder : RecyclerView.ViewHolder, Item, Header, Footer>() : RecyclerView.Adapter<ViewHolder>() {

    companion object {
        const val TYPE_HEADER = 0
        const val TYPE_ITEM = 1
        const val TYPE_FOOTER = 2
    }

    override fun getItemViewType(position: Int): Int {
        return when (position) {
            0 -> {
                header?.let {
                    TYPE_HEADER
                } ?: TYPE_ITEM
            }
            itemCount - 1 -> {
                footer?.let {
                    TYPE_FOOTER
                } ?: TYPE_ITEM
            }
            else -> TYPE_ITEM
        }
    }

    var header: Header? = null

    var footer: Footer? = null

    var items: ArrayList<Item> = ArrayList<Item>()

    fun addAll(items: List<Item>) {
        this.items.addAll(items)
    }

    val isEmpty: Boolean
        get() = items.isEmpty()

    override fun getItemCount(): Int {
        return items.size + headerCount() + footerCount()
    }

    fun headerCount() = header?.let { 1 } ?: 0

    fun footerCount() = (footer?.let { 1 } ?: 0)

    abstract fun onCreateHeaderViewHolder(parent: ViewGroup, viewType: Int): ViewHolder

    abstract fun onCreateItemViewHolder(parent: ViewGroup, viewType: Int): ViewHolder;

    abstract fun onCreateFooterViewHolder(parent: ViewGroup, viewType: Int): ViewHolder

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
        return when (viewType) {
            TYPE_HEADER -> onCreateHeaderViewHolder(parent, viewType)
            TYPE_FOOTER -> onCreateFooterViewHolder(parent, viewType)
            else -> onCreateItemViewHolder(parent, viewType)
        }
    }

    abstract fun onBindItemViewHolder(holder: ViewHolder, position: Int)

    abstract fun onBindHeaderViewHolder(holder: ViewHolder, position: Int)

    abstract fun onBindFooterViewHolder(holder: ViewHolder, position: Int)

    override fun onBindViewHolder(holder: ViewHolder, position: Int) {
        return when (getItemViewType(position)) {
            TYPE_HEADER -> onBindHeaderViewHolder(holder, position)
            TYPE_FOOTER -> onBindFooterViewHolder(holder, position)
            else -> onBindItemViewHolder(holder, position - headerCount())
        }
    }

}