MainActivity.kt

class MainActivity : AppCompatActivity() {

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

        val rootView: ViewGroup = findViewById(R.id.activity_main)

        val inflater = LayoutInflater.from(this)
        val red = inflater.inflate(R.layout.rectangle, rootView, true)
    }
}