A RecyclerView with multiple item types in Kotlin

It's been already 7 years ago that I wrote this article about multiple RecyclerView item types.

It got quite some views and responses, so I thought it would be nice to write a Kotlin version of this mini tutorial. You will see that it's a lot more compact than the old Java version.

So, here we go… Let's start with an interface for all the data types we have!

interface ListItem {
    enum class Type(value: Int) {TypeA(0), TypeB(1) }
    fun getListItemType(): Int
}

I'm still a bit in doubt if a sealed class would be a more elegant solution, but let's use an enum for now. We have a TypeA and a TypeB implementation and they look like this.

data class ItemA(val textA: String): ListItem {
    override fun getListItemType(): Int {
        return ListItem.Type.TypeA.ordinal
    }
}

And here is our Adapter!

class ItemAdapter(private val items: List<ListItem>) : RecyclerView.Adapter<BaseViewHolder>() {
    override fun getItemViewType(position: Int): Int {
        return items[position].getListItemType()
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): BaseViewHolder {
        return when (viewType) {
            ListItem.Type.TypeA.ordinal -> {
                val view = LayoutInflater.from(parent.context).inflate(R.layout.itemview_a, parent, false)
                return ViewHolderA(view)
            }
            ListItem.Type.TypeB.ordinal -> {
                val view = LayoutInflater.from(parent.context).inflate(R.layout.itemview_b, parent, false)
                return ViewHolderB(view)
            }
            else -> {
                val view = LayoutInflater.from(parent.context).inflate(R.layout.itemview_a, parent, false)
                return ViewHolderB(view)
            }
        }
    }

    override fun onBindViewHolder(holder: BaseViewHolder, position: Int) {
        holder.bind(items[position])
    }

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

I am not very happy with the fact that the onCreateViewHolder() function needs an else-statement which never will be reached. But since the RecyclerView is implemented with viewType as an Int I think we don't really have another option. But please leave a comment if you have a better solution for this!

Last but not least we need a ViewHolder abstraction. I made a BaseViewHolder with an abstract bind() function.

abstract class BaseViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
    abstract fun bind(item: ListItem)
}

And here's an example ViewHolder implementation.

class ViewHolderA(itemView: View) : BaseViewHolder(itemView) {
    private val textView: TextView = itemView.findViewById(R.id.text)

    override fun bind(item: ListItem) {
        val itemA = item as ItemA
        textView.text = itemA.textA
    }
}

Let me know what you think!