CompositeAdapter.kt

class CompositeAdapter : RecyclerView.Adapter<RecyclerView.ViewHolder>() {

    var adapters: List<RecyclerView.Adapter<RecyclerView.ViewHolder>> by adapterProperty(emptyList())

    fun addAdapter(adapter: RecyclerView.Adapter<out RecyclerView.ViewHolder>) {
        @Suppress("UNCHECKED_CAST")
        adapters = adapters.plus(adapter as RecyclerView.Adapter<RecyclerView.ViewHolder>)
        adapter.registerAdapterDataObserver(object : RecyclerView.AdapterDataObserver() {
            override fun onChanged() {
                notifyDataSetChanged()
            }
        })
    }

    override fun getItemCount(): Int {
        return adapters.sumBy { it.itemCount }
    }

    override fun getItemViewType(position: Int): Int {
        var currentPosition = position
        return adapters.indexOfFirst {
            (currentPosition < it.itemCount).apply {
                currentPosition -= it.itemCount
            }
        }
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder {
        return adapters[viewType].onCreateViewHolder(parent, 0)
    }

    override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
        var currentPosition = position
        val currentAdapter = adapters.first {
            (currentPosition < it.itemCount).apply {
                if (!this) currentPosition -= it.itemCount
            }
        }
        currentAdapter.onBindViewHolder(holder, currentPosition)
    }
}