我建议您使用AnimatedVisibility
小BottomNavigation
部件和TopAppBar
小部件,我认为这是最清晰的撰写方式。
- 您应该使用
remeberSaveable
来存储 BottomBar 和 TopAppBar 的状态:
// State of bottomBar, set state to false, if current page route is "car_details"
val bottomBarState = rememberSaveable { (mutableStateOf(true)) }
// State of topBar, set state to false, if current page route is "car_details"
val topBarState = rememberSaveable { (mutableStateOf(true)) }
- 在可组合函数中我们用于
when
控制BottomBar和TopAppBar的状态,下面我们设置bottomBarState
and topBarState
to true
,如果我们想显示BottomBar和TopAppBar,否则我们设置bottomBarState
and topBarState
to false
:
val navController = rememberNavController()
// Subscribe to navBackStackEntry, required to get current route
val navBackStackEntry by navController.currentBackStackEntryAsState()
// Control TopBar and BottomBar
when (navBackStackEntry?.destination?.route) {
"cars" -> {
// Show BottomBar and TopBar
bottomBarState.value = true
topBarState.value = true
}
"bikes" -> {
// Show BottomBar and TopBar
bottomBarState.value = true
topBarState.value = true
}
"settings" -> {
// Show BottomBar and TopBar
bottomBarState.value = true
topBarState.value = true
}
"car_details" -> {
// Hide BottomBar and TopBar
bottomBarState.value = false
topBarState.value = false
}
}
com.google.accompanist.insets.ui.Scaffold(
bottomBar = {
BottomBar(
navController = navController,
bottomBarState = bottomBarState
)
},
topBar = {
TopBar(
navController = navController,
topBarState = topBarState
)
},
content = {
NavHost(
navController = navController,
startDestination = NavigationItem.Cars.route,
) {
composable(NavigationItem.Cars.route) {
CarsScreen(
navController = navController,
)
}
composable(NavigationItem.Bikes.route) {
BikesScreen(
navController = navController
)
}
composable(NavigationItem.Settings.route) {
SettingsScreen(
navController = navController,
)
}
composable(NavigationItem.CarDetails.route) {
CarDetailsScreen(
navController = navController,
)
}
}
}
)
重要提示:来自 Accompanist 的 Scaffold,在 build.gradle 中初始化。我们使用 Accompanist 的 Scaffold,因为我们需要完全控制填充,例如,在 Compose 的默认 Scaffold 中,如果我们有 TopAppBar,我们不能禁用顶部内容的填充。在我们的例子中,它是必需的,因为我们有 TopAppBar 的动画,内容应该在 TopAppBar 下,我们手动控制每个页面的填充。来自 Accompanist 的文档:https ://google.github.io/accompanist/insets/ 。
- 放入
BottomNavigation
里面AnimatedVisibility
,设置visible
值bottomBarState
和设置enter
和exit
动画,在我的例子中,我slideInVertically
用于enter
动画和slideOutVertically
动画exit
:
AnimatedVisibility(
visible = bottomBarState.value,
enter = slideInVertically(initialOffsetY = { it }),
exit = slideOutVertically(targetOffsetY = { it }),
content = {
BottomNavigation {
val navBackStackEntry by navController.currentBackStackEntryAsState()
val currentRoute = navBackStackEntry?.destination?.route
items.forEach { item ->
BottomNavigationItem(
icon = {
Icon(
painter = painterResource(id = item.icon),
contentDescription = item.title
)
},
label = { Text(text = item.title) },
selected = currentRoute == item.route,
onClick = {
navController.navigate(item.route) {
popUpTo(navController.graph.findStartDestination().id) {
saveState = true
}
launchSingleTop = true
restoreState = true
}
}
)
}
}
}
)
- 放入
TopAppBar
里面AnimatedVisibility
,设置visible
值topBarState
和设置enter
和exit
动画,在我的例子中,我slideInVertically
用于enter
动画和slideOutVertically
动画exit
:
AnimatedVisibility(
visible = topBarState.value,
enter = slideInVertically(initialOffsetY = { -it }),
exit = slideOutVertically(targetOffsetY = { -it }),
content = {
TopAppBar(
title = { Text(text = title) },
)
}
)
MainActivity 的完整代码:
package codes.andreirozov.bottombaranimation
import android.os.Bundle
import androidx.activity.ComponentActivity
import androidx.activity.compose.setContent
import androidx.compose.animation.AnimatedVisibility
import androidx.compose.animation.ExperimentalAnimationApi
import androidx.compose.animation.slideInVertically
import androidx.compose.animation.slideOutVertically
import androidx.compose.material.*
import androidx.compose.runtime.*
import androidx.compose.runtime.saveable.rememberSaveable
import androidx.compose.ui.res.painterResource
import androidx.navigation.NavController
import androidx.navigation.NavGraph.Companion.findStartDestination
import androidx.navigation.compose.NavHost
import androidx.navigation.compose.composable
import androidx.navigation.compose.currentBackStackEntryAsState
import androidx.navigation.compose.rememberNavController
import codes.andreirozov.bottombaranimation.screens.BikesScreen
import codes.andreirozov.bottombaranimation.screens.CarDetailsScreen
import codes.andreirozov.bottombaranimation.screens.CarsScreen
import codes.andreirozov.bottombaranimation.screens.SettingsScreen
import codes.andreirozov.bottombaranimation.ui.theme.BottomBarAnimationTheme
@ExperimentalAnimationApi
class MainActivity : ComponentActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContent {
BottomBarAnimationApp()
}
}
}
@ExperimentalAnimationApi
@Composable
fun BottomBarAnimationApp() {
// State of bottomBar, set state to false, if current page route is "car_details"
val bottomBarState = rememberSaveable { (mutableStateOf(true)) }
// State of topBar, set state to false, if current page route is "car_details"
val topBarState = rememberSaveable { (mutableStateOf(true)) }
BottomBarAnimationTheme {
val navController = rememberNavController()
// Subscribe to navBackStackEntry, required to get current route
val navBackStackEntry by navController.currentBackStackEntryAsState()
// Control TopBar and BottomBar
when (navBackStackEntry?.destination?.route) {
"cars" -> {
// Show BottomBar and TopBar
bottomBarState.value = true
topBarState.value = true
}
"bikes" -> {
// Show BottomBar and TopBar
bottomBarState.value = true
topBarState.value = true
}
"settings" -> {
// Show BottomBar and TopBar
bottomBarState.value = true
topBarState.value = true
}
"car_details" -> {
// Hide BottomBar and TopBar
bottomBarState.value = false
topBarState.value = false
}
}
// IMPORTANT, Scaffold from Accompanist, initialized in build.gradle.
// We use Scaffold from Accompanist, because we need full control of paddings, for example
// in default Scaffold from Compose we can't disable padding for content from top if we
// have TopAppBar. In our case it's required because we have animation for TopAppBar,
// content should be under TopAppBar and we manually control padding for each pages.
com.google.accompanist.insets.ui.Scaffold(
bottomBar = {
BottomBar(
navController = navController,
bottomBarState = bottomBarState
)
},
topBar = {
TopBar(
navController = navController,
topBarState = topBarState
)
},
content = {
NavHost(
navController = navController,
startDestination = NavigationItem.Cars.route,
) {
composable(NavigationItem.Cars.route) {
// show BottomBar and TopBar
LaunchedEffect(Unit) {
bottomBarState.value = true
topBarState.value = true
}
CarsScreen(
navController = navController,
)
}
composable(NavigationItem.Bikes.route) {
// show BottomBar and TopBar
LaunchedEffect(Unit) {
bottomBarState.value = true
topBarState.value = true
}
BikesScreen(
navController = navController
)
}
composable(NavigationItem.Settings.route) {
// show BottomBar and TopBar
LaunchedEffect(Unit) {
bottomBarState.value = true
topBarState.value = true
}
SettingsScreen(
navController = navController,
)
}
composable(NavigationItem.CarDetails.route) {
// hide BottomBar and TopBar
LaunchedEffect(Unit) {
bottomBarState.value = false
topBarState.value = false
}
CarDetailsScreen(
navController = navController,
)
}
}
}
)
}
}
@ExperimentalAnimationApi
@Composable
fun BottomBar(navController: NavController, bottomBarState: MutableState<Boolean>) {
val items = listOf(
NavigationItem.Cars,
NavigationItem.Bikes,
NavigationItem.Settings
)
AnimatedVisibility(
visible = bottomBarState.value,
enter = slideInVertically(initialOffsetY = { it }),
exit = slideOutVertically(targetOffsetY = { it }),
content = {
BottomNavigation {
val navBackStackEntry by navController.currentBackStackEntryAsState()
val currentRoute = navBackStackEntry?.destination?.route
items.forEach { item ->
BottomNavigationItem(
icon = {
Icon(
painter = painterResource(id = item.icon),
contentDescription = item.title
)
},
label = { Text(text = item.title) },
selected = currentRoute == item.route,
onClick = {
navController.navigate(item.route) {
popUpTo(navController.graph.findStartDestination().id) {
saveState = true
}
launchSingleTop = true
restoreState = true
}
}
)
}
}
}
)
}
@ExperimentalAnimationApi
@Composable
fun TopBar(navController: NavController, topBarState: MutableState<Boolean>) {
val navBackStackEntry by navController.currentBackStackEntryAsState()
val title: String = when (navBackStackEntry?.destination?.route ?: "cars") {
"cars" -> "Cars"
"bikes" -> "Bikes"
"settings" -> "Settings"
"car_details" -> "Cars"
else -> "Cars"
}
AnimatedVisibility(
visible = topBarState.value,
enter = slideInVertically(initialOffsetY = { -it }),
exit = slideOutVertically(targetOffsetY = { -it }),
content = {
TopAppBar(
title = { Text(text = title) },
)
}
)
}
结果:
不要忘记使用 @ExperimentalAnimationApi 注释来编写函数。
更新:@ExperimentalAnimationApi
不需要Compose 版本 1.1.0 及更高版本。
2022 年 2 月 22 日更新:我做了一些研究,更新点 2。现在我们使用when
控制topBarState
和bottomBarState
.
gitHub 上提供的完整代码:
https ://github.com/AndreiRoze/BottomBarAnimation/tree/with_animated_topbar
官方文档中可用的动画示例:
https ://developer.android.com/jetpack/compose/animation