How to use RecyclerView inside PopupWindow

I have and simple app form (Android dev course) and I learn to use RecyclerView. The code works fine (if I use RecyclerView in MainActivity) but if I want to put that RecyclerView inside a PopupWindow, the app crashes (in most of my attempts: The specified child already has a parent, and I can't use removeView()).

So how can I use the RecyclerView inside PopupWindow?

This is ItemAdapter:

class ItemAdapter(
    private val context: Context,
    private val dataset: List<Affirmation>
) : RecyclerView.Adapter<ItemAdapter.ItemViewHolder>() {

    class ItemViewHolder(private val view: View) : RecyclerView.ViewHolder(view) {
        val textView: TextView = view.findViewById(R.id.item_title)

    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ItemViewHolder {
        val adapterLayout = LayoutInflater.from(parent.context)
            .inflate(R.layout.list_item, parent, false)

        return ItemViewHolder(adapterLayout)
    }

    override fun onBindViewHolder(holder: ItemViewHolder, position: Int) {
        val item = dataset[position]
        holder.textView.text =  context.resources.getString(item.stringResourceId)

    }

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

This is MainActivity:

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val myDataset = Datasource().loadAffirmations()

        val btn = findViewById<Button>(R.id.button)
        btn.setOnClickListener {

            val popup_window = PopupWindow(this)
            val inflator = layoutInflater.inflate(R.layout.popup_list, null)
            
            popup_window.contentView = ???
            
            popup_window.showAsDropDown(btn)
            
}}}

This is popup_list.xml:

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recycler_view"
        app:layoutManager="LinearLayoutManager"
        android:scrollbars="vertical"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
</FrameLayout>

list_item.xml is a simple TextView and in activity_main.xml I have just a Button for open the PopupWindow

Update this and you should see a pop window below button.

popup_window.contentView = inflator.rootView

After that it logcat will print No adapter attached; skipping layout thats where you initiate your reyclerview and adapter and attach the adapter to your recyclerview inside popup_list.

I am not going to be in very detail as this answer is very well asked and answered Here.