22. Compose NestedScroll 向下滑动隐藏标题

val toolbarHeight = 48.dp
        val toolbarHeightPx = with(LocalDensity.current) { toolbarHeight.roundToPx().toFloat() }
        val toolbarOffsetHeightPx = remember { mutableStateOf(0f) }
        val nestedScrollConnection = remember {
            object : NestedScrollConnection {
                override fun onPreScroll(available: Offset, source: NestedScrollSource): Offset {
                    //y方向的偏移量
                    val delta = available.y
                    val newOffset = toolbarOffsetHeightPx.value + delta
                    toolbarOffsetHeightPx.value = newOffset.coerceIn(-toolbarHeightPx, 0f)
                    return Offset.Zero
                }
            }
        }
        Box(
            Modifier
                .fillMaxSize()
                .nestedScroll(nestedScrollConnection)
        ) {
            LazyColumn(contentPadding = PaddingValues(top = toolbarHeight)) {
                items(100) { index ->
                    Text(
                        stringResource(id = R.string.nested_scroll, index),
                        modifier = Modifier
                            .fillMaxWidth()
                            .padding(16.dp)
                    )
                }
            }
            TopAppBar(
                modifier = Modifier
                    .height(toolbarHeight)
                    .offset { IntOffset(x = 0, y = toolbarOffsetHeightPx.value.roundToInt()) },
                title = {
                    Text(
                        stringResource(id = R.string.app_name, toolbarOffsetHeightPx.value)
                    )
                }
            )
        }