Not able to extend Adapter from a custom ResyclerView in Kotlin

Question

I'm trying to implement an empty state recycler view based on this post. I have migrated the solution to Kotlin, but the problem is I'm not able to extend CustomRecyclerView.Adapter (Adapter is an abstract class defined in RecyclerView) from the newly defined custom recycler view in Kotlin. And I have observed the same CustomRecyclerView.Adapter can be extended in Java.

Custome RecyclerView implementation

open class CustomRecyclerView: RecyclerView {


private var emptyStateView : View? = null

constructor(context: Context) : super(context)
constructor(context: Context , attrs: AttributeSet) : super(context,attrs)
constructor(context: Context , attrs: AttributeSet, defstyle: Int) : super(context,attrs,defstyle)


var observer: AdapterDataObserver = object : AdapterDataObserver() {

    override fun onChanged() {
        super.onChanged()
        initEmptyView()
    }

    override fun onItemRangeRemoved(positionStart: Int, itemCount: Int) {
        super.onItemRangeRemoved(positionStart, itemCount)
        initEmptyView()
    }

    override fun onItemRangeInserted(positionStart: Int, itemCount: Int) {
        super.onItemRangeInserted(positionStart, itemCount)
        initEmptyView()
    }
}

private fun initEmptyView() {
    emptyStateView?.let {
        it.visibility = if (adapter == null || adapter!!.itemCount == 0) View.VISIBLE else View.GONE
        this@CustomRecyclerView.visibility = if (adapter == null || adapter!!.itemCount == 0) View.GONE else View.VISIBLE
    }
}

override fun setAdapter(adapter: Adapter<*>?) {
    val oldAdapter = getAdapter()
    super.setAdapter(adapter)
    oldAdapter?.unregisterAdapterDataObserver(observer)
    adapter?.registerAdapterDataObserver(observer)
}

/**
 * @param emptyView is the view which is going to display when the recycler view is empty
 * **/
fun setEmptyView(emptyView: View) {
    this.emptyStateView = emptyView
    initEmptyView()
}}

Adding images for the extension implementation in java and kotin

Answer 1

To summarise the comments: inherit from RecyclerView.Adapter, see below

YourAdapter: RecyclerView.Adapter<YourViewHolder>()

And just a hint, here's the Kotlin way to extend a class with multiple constructors:

class CustomRecyclerView @JvmOverloads constructor(
        context: Context,
        attrs: AttributeSet? = null,
        defStyleAttr: Int = 0
) : RecyclerView(context, attrs, defStyleAttr)

For more info, check @JvmOverloads