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使用枚举与密封类表示状态

安全地建模固定选项和结果变体

使用枚举与密封类表示状态 是 CoddyKit 上的免费 Kotlin Multiplatform 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 Kotlin Multiplatform Academy 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 Kotlin Multiplatform 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。

Model Fixed Choices

Some values have a known, limited set of options. Kotlin gives you enums and sealed classes to model them safely in shared code.

Meet the enum class

An enum class lists every allowed value by name. Nothing outside that list can ever sneak in.

enum class Status { ACTIVE, PAUSED, DONE }

Use an enum Value

Refer to an option by its name. Because the set is closed, your state is always one of the listed cases.

val current = Status.ACTIVE

Enums Can Carry Data

Give an enum constructor properties so each case can hold extra fixed info, like a label or numeric code.

enum class Plan(val price: Int) { FREE(0), PRO(9) }

When Cases Need Different Data

Enums share one shape. When variants need different fields, reach for a sealed class instead.

Meet the sealed class

A sealed class defines a closed family of subtypes. Each subtype can carry its own distinct data.

sealed class Result
data class Ok(val value: String) : Result()
data class Err(val message: String) : Result()

Why Sealed Is Powerful

Because the compiler knows every subtype, a sealed class models success, loading and error states with type-safe payloads.

val state: Result = Ok("loaded")

Match with when

Handle each case using when. The compiler checks you covered every variant of the sealed type.

when (state) {
  is Ok -> println(state.value)
  is Err -> println(state.message)
}

Exhaustive when, No else

When you handle all sealed cases, you can drop the else branch. Add a new subtype later and the compiler reminds you.

Shared, So Both Apps Agree

Defined in commonMain, these state types drive identical logic on Android and iOS with zero drift.

Pick the Right Tool

Use an enum for simple fixed options, and a sealed class when each case carries different data.

Quick Check

Which type should model these states?

Recap

Use shared enums for fixed options and sealed classes for variants with their own data, then match them safely with when.

常见问题解答

「使用枚举与密封类表示状态」课时是免费的吗？

是的 — 「使用枚举与密封类表示状态」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 Kotlin Multiplatform Academy 课程的其余内容，请升级到 CoddyKit PRO。 Kotlin Multiplatform Academy 课程共包含 4 节课。

「使用枚举与密封类表示状态」这节课中我会学到什么？

安全地建模固定选项和结果变体你通过在浏览器中直接运行的动手代码来练习 Kotlin Multiplatform 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 Kotlin Multiplatform Academy 需要有经验吗？

无需任何先前经验。CoddyKit 上的 Kotlin Multiplatform 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。

「使用枚举与密封类表示状态」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 Kotlin Multiplatform Academy 课中编写并运行代码吗？

能。每节 Kotlin Multiplatform 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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