//////////////////////////////////////   activity MainActivity.kt
class MainActivity : AppCompatActivity() {

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

        //setSupportActionBar(toolbar)


        btnAdd2.setOnClickListener() {

            val dialogBuilder = AlertDialog.Builder(this@MainActivity)
            val title = dialogBuilder.setTitle("Adicione um produto")
            val view = layoutInflater.inflate(R.layout.content_main, null)
            dialogBuilder.setView(view)
            val alertDialog = dialogBuilder.create()
            alertDialog.show()

            //chamar nova atividade
            /*val it = Intent(this@MainActivity, content::class.java)
            startActivity(it)*/

        }


    }
}


//////////////////////////////////////   activity content.kt

class content: AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.content_main)

        val quant = arrayOf("1","2","3","4")
        val spin = findViewById<Spinner>(R.id.txtQuant)
        val arrayQuant = ArrayAdapter(this@content,android.R.layout.simple_spinner_dropdown_item, quant)
        spin.adapter = arrayQuant
}


}

///////////////////////////////////////////// content_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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:id="@+id/itemnametxt"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    tools:context="layout.content"
    android:padding="16dp">

    <EditText
        android:id="@+id/txtName"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

    <Spinner
        android:id="@+id/txtQuant"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentStart="true"
        android:layout_below="@+id/txtName"
        android:layout_marginTop="18dp"
        android:spinnerMode="dialog" />



</RelativeLayout>