当我制作动画时，底部栏导航给出白色背景

问题原来是“paddingValues”：当“bottomBar”的可见性发生变化时，“Scaffold”更新“paddingValues”，这导致“背景”在动画开始之前出现。

解决方案是也为“paddingValues”设置动画：

class MainActivity : ComponentActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        enableEdgeToEdge()


        setContent {
            Test_delete_itTheme {
                var isBottomBarVisible: Boolean by remember { mutableStateOf(false) }

                LaunchedEffect(Unit) {
                    while (true) {
                        delay(2000)
                        isBottomBarVisible = !isBottomBarVisible
                    }
                }

                Scaffold(
                    modifier = Modifier.fillMaxSize(),
                    bottomBar = {
                        AnimatedVisibility(
                            modifier = Modifier,
                            visible = isBottomBarVisible,
                            enter = slideInVertically(
                                initialOffsetY = { it },
                                animationSpec = tween(
                                    durationMillis = 500,
                                    easing = FastOutSlowInEasing
                                )
                            ),
                            exit = slideOutVertically(
                                targetOffsetY = { it },
                                animationSpec = tween(
                                    durationMillis = 300,
                                    easing = FastOutSlowInEasing
                                )
                            )
                        ) {
                            NavigationBar(
                                containerColor = Color.Red,
                            ) {
                                repeat(3) {
                                    NavigationBarItem(
                                        modifier = Modifier,
                                        icon = {
                                            Icon(
                                                modifier = Modifier,
                                                painter = painterResource(android.R.drawable.ic_menu_add),
                                                contentDescription = null,
                                            )
                                        },
                                        selected = false,
                                        onClick = { }
                                    )
                                }
                            }
                        }
                    }
                ) { innerPadding ->
                    val targetPadding: PaddingValues = if (isBottomBarVisible) {
                        innerPadding
                    } else {
                        PaddingValues(
                            top = innerPadding.calculateTopPadding(),
                            bottom = 0.dp,
                            start = innerPadding.calculateStartPadding(LayoutDirection.Ltr),
                            end = innerPadding.calculateEndPadding(LayoutDirection.Ltr)
                        )
                    }

                    val animatedStartPadding by animatePaddingValue(targetPadding.calculateStartPadding(LayoutDirection.Ltr), isBottomBarVisible)
                    val animatedTopPadding by animatePaddingValue(targetPadding.calculateTopPadding(), isBottomBarVisible)
                    val animatedEndPadding by animatePaddingValue(targetPadding.calculateEndPadding(LayoutDirection.Ltr), isBottomBarVisible)
                    val animatedBottomPadding by animatePaddingValue(targetPadding.calculateBottomPadding(), isBottomBarVisible)

                    Box(
                        modifier = Modifier
                            .fillMaxSize()
                            .padding(
                                start = animatedStartPadding,
                                top = animatedTopPadding,
                                end = animatedEndPadding,
                                bottom = animatedBottomPadding
                            )
                            .background(Color.Green)
                    ) {

                    }
                }
            }
        }
    }
}

@Composable
private fun animatePaddingValue(targetValue: Dp, isBottomBarVisible: Boolean): androidx.compose.runtime.State<Dp> {
    val animationSpec = tween<Dp>(
        durationMillis = if (isBottomBarVisible) 500 else 300,
        easing = FastOutSlowInEasing
    )
    return animateDpAsState(targetValue = targetValue, animationSpec = animationSpec, label = "")
}