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使用 value 与 onValueChange 提升状态

向下传递状态，向上传递事件。

使用 value 与 onValueChange 提升状态 是 CoddyKit 上的免费 Jetpack Compose Academy 课时。 这是第 2 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。

State Hoisting in One Line

State hoisting means moving state out of a Composable up to its caller. The component becomes stateless and the parent stays in charge.

The Core Pattern

Replace internal state with two parameters: a value to display and an onValueChange callback to report changes.

fun NameField(value: String, onValueChange: (String) -> Unit) {
  TextField(value = value, onValueChange = onValueChange)
}

State Down, Events Up

Data flows down through value; user actions flow up through onValueChange. This one-way loop is called unidirectional data flow. ↕️

Who Owns the State Now

The parent owns the state with remember and passes it in. The child never stores it, so two callers can drive the same component differently.

var name by remember { mutableStateOf("") }
NameField(value = name, onValueChange = { name = it })

value: The Read Side

The value parameter is what the component shows right now. It is read-only to the child; the child never edits it directly.

onValueChange: The Write Side

When the user types, the child calls onValueChange(newText). The parent decides whether and how to update its state.

Why Not Edit In Place

A stateless child cannot just reassign value, it is only an input. Reporting the change upward keeps a single owner in control.

Controlled Components

This is a controlled component: the parent fully decides what shows. You can transform, ignore, or validate input before storing it.

NameField(value = name, onValueChange = { name = it.uppercase() })

Reusing the Same Field

Because the field is hoisted, you can drop it into a login screen, a search bar, or a settings page, each with its own owning state.

Hoisting Beyond Text

The pattern fits any state: a checked Boolean with onCheckedChange, a selected item with onSelect. Same idea, different names.

fun ToggleRow(checked: Boolean, onCheckedChange: (Boolean) -> Unit) {
  Switch(checked = checked, onCheckedChange = onCheckedChange)
}

A Simple Rule

Hoist state to the lowest common parent that needs to read or change it, no higher. That keeps ownership clear and code clean.

Quick Check

In the hoisting pattern, what does the child do when the user types?

Recap

Hoisting swaps internal state for value plus onValueChange. State flows down, events flow up, and the parent stays in charge. 🚀

常见问题解答

「使用 value 与 onValueChange 提升状态」课时是免费的吗？

是的 — 「使用 value 与 onValueChange 提升状态」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。

「使用 value 与 onValueChange 提升状态」这节课中我会学到什么？

向下传递状态，向上传递事件。 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 2 节课，共 4 节。

「使用 value 与 onValueChange 提升状态」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。

此课程中的所有课时

  1. 有状态与无状态 Composable
  2. 使用 value 与 onValueChange 提升状态
  3. 单一真实来源
  4. Compose 状态插槽与内容 Lambda
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