切换时保留标签页状态
保留每个标签页的滚动位置和状态。
切换时保留标签页状态 是 CoddyKit 上的免费 Jetpack Compose Academy 课时。 这是第 3 节课，共 4 节。 你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。 这是 Jetpack Compose Academy 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 Jetpack Compose Academy 课程共包含 4 节课。
本课时的部分内容尚未翻译，以英文显示。
The Lost Scroll Problem
By default, leaving a tab and coming back rebuilds it from scratch, so your scroll position and inputs vanish. Annoying, right? 😅
Why It Happens
A plain navigate replaces the destination, so Compose forgets the old screen. Preserving state means telling navigation to save it instead.
Save on the Way Out
When you pop the old tab, add saveState so its UI state is stored rather than thrown away.
popUpTo(startRoute) {
saveState = true
}Restore on the Way In
When you navigate to the tab, set restoreState so its previously saved state comes right back.
navController.navigate(tab.route) {
restoreState = true
}The Three-Flag Combo
Together saveState, restoreState, and launchSingleTop give the classic, smooth tab-switching behavior users expect.
popUpTo(start) { saveState = true }
launchSingleTop = true
restoreState = truerememberSaveable Helps Too
For values inside a screen, rememberSaveable keeps things like text fields alive across recreation, complementing nav state saving.
var query by rememberSaveable { mutableStateOf("") }Lists Need Saved Scroll
A LazyColumn keeps its scroll when you use rememberLazyListState, and saved nav state lets that survive a tab round-trip.
val listState = rememberLazyListState()
LazyColumn(state = listState) { /* ... */ }Watch the Start Route
Always pop up to the same start destination id so the saved-state bundles map back to the correct tab.
popUpTo(navController.graph.findStartDestination().id)Verify by Switching
Test it: scroll one tab, jump to another, then return. With the flags set, the scroll should be exactly where you left it.
When Not to Restore
Sometimes a tab should refresh on entry, like a feed. Then simply skip restoreState for that route and let it rebuild.
State Beyond One Screen
For data that must outlive even the tab, lift it into a shared ViewModel so navigation flags only handle UI, not your real data.
Quick Check
You learned to keep each tab fresh. Time for a check.
Recap
You kept tabs sticky: saveState + restoreState + launchSingleTop preserve scroll and input, with rememberSaveable backing up in-screen values. Smooth! ✨
常见问题解答
「切换时保留标签页状态」课时是免费的吗？
是的 — 「切换时保留标签页状态」的完整文本可在网页上免费阅读。要进行交互式练习（内置代码编辑器和全天候 AI 导师）并解锁 Jetpack Compose Academy 课程的其余内容，请升级到 CoddyKit PRO。 Jetpack Compose Academy 课程共包含 4 节课。
「切换时保留标签页状态」这节课中我会学到什么？
保留每个标签页的滚动位置和状态。 你通过在浏览器中直接运行的动手代码来练习 Jetpack Compose Academy，全天候 AI 导师会在你学习这节课的过程中回答你的问题。
学习 Jetpack Compose Academy 需要有经验吗？
无需任何先前经验。CoddyKit 上的 Jetpack Compose Academy 课程适合初学者到高级学习者，你可以从这里开始或从头开始，按照自己的节奏学习。 这是第 3 节课，共 4 节。
「切换时保留标签页状态」课时需要多长时间？
大多数 CoddyKit 课程大约需要 5–10 分钟。每节课都很精短且互动，所以你能稳步进步，并在网页和应用中从离开的地方继续。
我能在这节 Jetpack Compose Academy 课中编写并运行代码吗？
能。每节 Jetpack Compose Academy 课都包含内置代码编辑器，你可以在浏览器中直接编写并运行真实代码，并获得即时 AI 反馈 — 无需本地设置。