Example adapter that uses a ListAdapterWithHeader

ExampleAdapter.kt

package example

import android.support.v7.util.DiffUtil
import android.support.v7.widget.RecyclerView
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import example.R
import example.ListAdapterWithHeader

class ExampleAdapter : ListAdapterWithHeader<YourDataItem, RecyclerView.ViewHolder>(ITEM_COMPARATOR) {

    private var headerItem: HeaderDataItem = HeaderDataItem("Some header data")

    // Updates the header item view
    fun setHeaderItem(newHeaderItem: HeaderDataItem) {
        val previousItem = this.headerItem
        this.headerItem = newHeaderItem
        if (previousItem != newHeaderItem) {
            notifyItemChanged(HEADER_POSITION)
        }
    }

    // Returns the type of view at the given list position
    override fun getItemViewType(position: Int): Int {
        return if (position == HEADER_POSITION) {
            R.layout.item_header_row // header layout not included in example
        } else {
            R.layout.item_data_row // data item layout not included in example
        }
    }

    // Creates a view holder for the given viewType
    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder {
        return when (viewType) {
            R.layout.item_header_row -> HeaderItemViewHolder.create(parent)
            R.layout.item_data_row -> DataItemViewHolder.create(parent)
            else -> throw IllegalArgumentException("Unknown view type $viewType")
        }
    }

    // Binds a view holder to the data at the given list position
    override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
        return when (getItemViewType(position)) {
            R.layout.item_header_row -> (holder as HeaderItemViewHolder).bindTo(headerItem)
            else -> (holder as DataItemViewHolder).bind(getItem(position))
        }
    }

    companion object {
        // The position of the header in the zero-based list
        const val HEADER_POSITION = 0

        // A DiffUtil.ItemCallback for calculating the diff between two non-null items in a list.
        val ITEM_COMPARATOR = object : DiffUtil.ItemCallback<YourDataItem>() {
            override fun areContentsTheSame(
                oldItem: YourDataItem,
                newItem: YourDataItem
            ): Boolean {
                return oldItem == newItem
            }

            override fun areItemsTheSame(
                oldItem: YourDataItem,
                newItem: YourDataItem
            ): Boolean {
                return oldItem.itemId == newItem.itemId
            }
        }
    }
}

// A class holding header data
data class HeaderDataItem(
    val someHeaderData: String
)

// A view holder for displaying the header row data
class HeaderItemViewHolder(view: View) : RecyclerView.ViewHolder(view) {
    fun bindTo(headerItem: HeaderDataItem) {
        // TODO : display the headerItem.someHeaderData
    }

    companion object {
        fun create(parent: ViewGroup): HeaderItemViewHolder {
            val view = LayoutInflater.from(parent.context)
                .inflate(R.layout.item_header_row, parent, false)
            return HeaderItemViewHolder(view)
        }
    }
}

// A class that holds the data items in your list
data class YourDataItem(
    val itemId: Long,
    val someData: String
)

// A view holder for displaying the item row data
class DataItemViewHolder(view: View) : RecyclerView.ViewHolder(view) {
    fun bind(dataItem: YourDataItem) {
        // TODO : display the dataItem.someData
    }

    companion object {
        fun create(parent: ViewGroup): HeaderItemViewHolder {
            val view = LayoutInflater.from(parent.context)
                .inflate(R.layout.item_data_row, parent, false)
            return HeaderItemViewHolder(view)
        }
    }
}