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带多个标签页的 NavigationBar

在底部切换顶层区域。

带多个标签页的 NavigationBar 是 CoddyKit 上的免费 Jetpack Compose Academy 课时。这是第 1 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。

Meet NavigationBar

Material 3 gives you NavigationBar, a bar pinned to the bottom that lets people jump between the top-level sections of your app. 📱

When to Use It

Reach for a NavigationBar when your app has three to five equally important destinations, like Home, Search, and Profile.

It Lives in the Scaffold

You usually drop the bar into a Scaffold bottomBar slot, so it stays fixed while the screen content scrolls above it.

Scaffold(
  bottomBar = { NavigationBar { /* items */ } }
) { padding -> Content(padding) }

Each Tab Is an Item

Inside the bar you add one NavigationBarItem per destination. Each item is a clickable tab with its own icon and label.

NavigationBar {
  NavigationBarItem(/* ... */)
  NavigationBarItem(/* ... */)
}

The selected Flag

Every item needs a selected boolean. Exactly one item should be true at a time so the bar shows where the user is.

NavigationBarItem(
  selected = current == "home",
  onClick = { go("home") }
)

Handle the Tap

The onClick lambda runs when the tab is pressed. This is where you tell your navigation to switch to that section.

Give It an Icon

The icon slot takes a Composable, usually an Icon from the Material set, so each tab is instantly recognizable.

icon = { Icon(Icons.Default.Home, contentDescription = "Home") }

Add a Label

The label slot shows short text under the icon. Keep it to one clear word so it fits and reads fast.

label = { Text("Home") }

A Model for Tabs

It helps to keep your tabs in a simple data class list, so the bar can loop over them instead of hard-coding each item.

data class Tab(val route: String, val icon: ImageVector, val label: String)

Loop to Build the Bar

With a tab list you can forEach over it and emit one NavigationBarItem per entry, keeping the bar tidy and easy to extend.

tabs.forEach { tab ->
  NavigationBarItem(/* uses tab fields */)
}

Pair It with Content

The bar only switches the active section. You still pair it with a NavHost or a when block that actually swaps the screen content.

Quick Check

You added three tabs to your NavigationBar. Quick check on the basics.

Recap

You met NavigationBar: drop it in the Scaffold, add a NavigationBarItem per section with an icon, label, selected flag, and onClick. Nice work! 🎉

常见问题解答

「带多个标签页的 NavigationBar」课时是免费的吗？

是的 — 「带多个标签页的 NavigationBar」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。

「带多个标签页的 NavigationBar」这节课中我会学到什么？

在底部切换顶层区域。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 1 节课，共 4 节。

「带多个标签页的 NavigationBar」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。

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