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定义 Retrofit API 接口

使用注解声明端点。

定义 Retrofit API 接口 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。

What Retrofit Does

Retrofit turns a plain Kotlin interface into a working HTTP client, so you describe your API and it writes the networking code for you.

It Starts With an Interface

You declare each endpoint as a function inside a Kotlin interface. Retrofit reads the annotations and builds the real implementation at runtime.

interface UserApi {
    // endpoint functions go here
}

Mark a GET Request

The @GET annotation tells Retrofit this function fetches data. You pass the path that sits after your base URL. 🌐

@GET("users")
fun getUsers(): Call<List<User>>

POST, PUT and DELETE Too

Beyond GET, Retrofit offers @POST, @PUT, and @DELETE so one interface can read and write data on your server.

@POST("users")
fun createUser(@Body user: User): Call<User>

Path Parameters

Use @Path to inject a value into the URL. Retrofit swaps the named placeholder in braces for the argument you pass in.

@GET("users/{id}")
fun getUser(@Path("id") id: Int): Call<User>

Query Parameters

Add @Query for values after the question mark, like search terms or page numbers. Retrofit appends them to the URL for you.

@GET("search")
fun search(@Query("q") term: String): Call<Result>

The Return Type

The function's return type tells Retrofit what shape to expect back. A data class here maps straight onto the JSON response.

@GET("users/{id}")
fun getUser(@Path("id") id: Int): Call<User>

Set the Base URL

You build one Retrofit instance with the base URL. Every endpoint path you declared is joined onto it automatically.

val retrofit = Retrofit.Builder()
    .baseUrl("https://api.example.com/")
    .build()

Create the Implementation

Call create with your interface class and Retrofit returns a ready-to-use object. You never write the request code yourself.

val api = retrofit.create(UserApi::class.java)

Add a Converter Factory

A converter factory teaches Retrofit how to turn JSON into your data classes. You add it once when building the instance.

.addConverterFactory(MoshiConverterFactory.create())

Don't Forget the Permission

To reach the network, declare the INTERNET permission in your manifest. Without it, every request fails before it even starts.

<uses-permission android:name="android.permission.INTERNET" />

Quick Check

Which annotation injects a value directly into the URL path?

Recap: Your API Interface

You described endpoints as annotated interface functions, set a base URL, added a converter, and let Retrofit build the client. Next you'll parse the JSON it returns.

常见问题解答

「定义 Retrofit API 接口」课时是免费的吗？

是的 — 「定义 Retrofit API 接口」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。

「定义 Retrofit API 接口」这节课中我会学到什么？

使用注解声明端点。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。

「定义 Retrofit API 接口」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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