CenterAlignedTopAppBar won't scroll. What am I doing wrong?

Question

I am trying to add a scrollable behavior to the topBar parameter of Scaffold. In the documentation it says, that I can add the scrollable behavior by setting the CenterAlignedTopAppBar parameter scrollBehavior. However it doesn't seem to work.

The following answer from StackOverflow didn't help.

Any advice appreciated.

Here is how my code goes.

@Composable
fun Screen() {
    val topAppBarScrollBehavior = TopAppBarDefaults.enterAlwaysScrollBehavior(
        rememberTopAppBarState(),
        { true },
        spring(Spring.StiffnessMediumLow),
        rememberSplineBasedDecay()
    )
    val scrollBehavior = remember { topAppBarScrollBehavior }

    Scaffold(
        topBar = {
            ThemedTopBar(scrollBehavior, title = "Select Guests", onBack = {/* TODO */})
        }
    ) { innerPadding ->
        //MainContent(innerPadding) 
      }
}

@Composable
fun ThemedTopBar(scrollBehavior: TopAppBarScrollBehavior, title: String, onBack: () -> Unit) {
    CenterAlignedTopAppBar(
        modifier = Modifier
            .height(51.dp)
            .padding(vertical = 16.dp, horizontal = 9.dp)
        ,
        title = {
            Text(
                text = title,
                maxLines = 1,
                overflow = TextOverflow.Ellipsis,
                style = Typography.titleMedium
            )
        },
        navigationIcon = {
            IconButton(
                modifier = Modifier.size(22.dp),
                onClick = onBack,
            ) {
                Icon(
                    painter = painterResource(id = R.drawable.ic_baseline_arrow_back),
                    contentDescription = "Back Button",
                    tint = ThemeBlue
                )
            }
        },
        scrollBehavior = scrollBehavior
    )
}

Answer 1

You have to attach the TopAppBarScrollBehavior.nestedScrollConnection to a Modifier.nestedScroll in order to keep track of the scroll events.

Something like:

val scrollBehavior = TopAppBarDefaults.enterAlwaysScrollBehavior()
Scaffold(
    modifier = Modifier.nestedScroll(scrollBehavior.nestedScrollConnection),
    topBar = {
        CenterAlignedTopAppBar(
            title = { /* .. */ },
            navigationIcon = { /* .. */ },
            actions = { /* .. */ },
            scrollBehavior = scrollBehavior
        )
    },
    content = { /* .. */ }
)