Second v

MainActivity.kt

class MainActivity : ComponentActivity(R.layout.activity_main) {
    private var count: Int = 0

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        savedInstanceState?.let { state ->
            count = state.getInt("COUNT", 0)
        }

        textView.text = "$count"
        button.setOnClickListener {
            count++
            textView.text = "$count"
        }
    }

    override fun onSaveInstanceState(outState: Bundle) {
        outState.putInt("COUNT", count)
        super.onSaveInstanceState(outState)
    }
}