I’m learning how to develop an Android app using Jetpack Compose, and I’m currently working through understanding the activity lifecycle. I noticed an unexpected behavior: my @Composable function is being called after the onResume method, instead of right after onCreate.

Here is the relevant part of my code:

class MainActivity : ComponentActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        Log.i("LifeCycle", "We are in onCreate!")

        enableEdgeToEdge()
        setContent {
            ContatoreApp()
        }
    }

    override fun onStart() {
        super.onStart()
        Log.i("LifeCycle", "We are in onStart!")
    }

    override fun onResume() {
        super.onResume()
        Log.i("LifeCycle", "We are in onResume!")
    }

    override fun onPause() {
        super.onPause()
        Log.i("LifeCycle", "We are in onPause!")
    }

    override fun onStop() {
        super.onStop()
        Log.i("LifeCycle", "We are in onStop!")
    }

    override fun onRestart() {
        super.onRestart()
        Log.i("LifeCycle", "We are in onRestart!")
    }

    override fun onDestroy() {
        Log.i("LifeCycle", "We are in onDestroy!")
        super.onDestroy()
    }
}

@Composable
fun ContatoreApp() {
    Log.i("LifeCycle", "We are creating the UI!")
    var value by remember { mutableIntStateOf(0) }

    Scaffold(modifier = Modifier.fillMaxSize()) { innerPadding ->
        Column(
            modifier = Modifier
                .padding(innerPadding)
                .fillMaxSize(),
            verticalArrangement = Arrangement.SpaceEvenly,
            horizontalAlignment = Alignment.CenterHorizontally
        ) {
            Text(
                text = stringResource(R.string.contatore, value),
                fontSize = 30.sp
            )
            Button(onClick = { value++ }) {
                Text(
                    text = stringResource(R.string.incrementa),
                    modifier = Modifier.padding(10.dp),
                    fontSize = 30.sp
                )
            }
        }
    }
}

In the logs, I see the following sequence:

2024-07-12 16:16:57.970 30565-30565 LifeCycle           I  We are in onCreate!
2024-07-12 16:16:58.146 30565-30565 LifeCycle           I  We are in onStart!
2024-07-12 16:16:58.151 30565-30565 LifeCycle           I  We are in onResume!
2024-07-12 16:16:58.819 30565-30565 LifeCycle           I  We are creating the UI!

Why is the @Composable function being called after onResume instead of immediately after onCreate? Shouldn’t the UI be set up during onCreate when setContent is called?