# 发送网络数据

> 如何通过 http package 发送网络数据。



<?code-excerpt path-base="cookbook/networking/send_data/"?>

Sending data to the internet is necessary for most apps.
The `http` package has got that covered, too.

对于大部分应用来说，向互联网发送数据都是必不可少的。
`http` package 同样可以满足这一需求。

This recipe uses the following steps:

本教程包含以下步骤：

  1. Add the `http` package.

     添加 `http` package。

  2. Send data to a server using the `http` package.

     使用 `http` package 向服务器发送数据。

  3. Convert the response into a custom Dart object.

     将响应转换成一个自定义的 Dart 对象。

  4. Get a `title` from user input.

     从用户输入获取 `title`。

  5. Display the response on screen.

     在屏幕上显示响应。

## 1. Add the `http` package

## 1. 添加 `http` package

To add the `http` package as a dependency,
run `flutter pub add`:

要将 `http` package 添加为依赖，
请运行 `flutter pub add`：

```console
$ flutter pub add http
```

Import the `http` package.

导入 `http` package。

<?code-excerpt "lib/main.dart (Http)"?>
```dart
import 'package:http/http.dart' as http;
```

If you are deploying to Android, edit your `AndroidManifest.xml` file to
add the Internet permission.

如果你要部署 Android，
请编辑 `AndroidManifest.xml` 文件，
添加 Internet 权限。

```xml
<!-- Required to fetch data from the internet. -->
<uses-permission android:name="android.permission.INTERNET" />
```

Likewise, if you are deploying to macOS, edit your
`macos/Runner/DebugProfile.entitlements` and `macos/Runner/Release.entitlements`
files to include the network client entitlement.

同样，如果你要部署 macOS，
请编辑 `macos/Runner/DebugProfile.entitlements` 和 
`macos/Runner/Release.entitlements` 文件，
添加 network client 权限。

```xml
<!-- Required to fetch data from the internet. -->
<key>com.apple.security.network.client</key>
<true/>
```


## 2. Sending data to server

## 2. 向服务器发送数据

This recipe covers how to create an `Album`
by sending an album title to the
[JSONPlaceholder][] using the
[`http.post()`][] method.

本教程介绍如何使用 [`http.post()`][] 方法
将相册标题发送到 [JSONPlaceholder][] 以创建 `Album`。

Import `dart:convert` for access to `jsonEncode` to encode the data:

导入 `dart:convert` 以使用 `jsonEncode` 编码数据：

<?code-excerpt "lib/create_album.dart (convert-import)"?>
```dart
import 'dart:convert';
```

Use the `http.post()` method to send the encoded data:

使用 `http.post()` 方法发送编码后的数据：

<?code-excerpt "lib/create_album.dart (CreateAlbum)"?>
```dart
Future<http.Response> createAlbum(String title) {
  return http.post(
    Uri.parse('https://jsonplaceholder.typicode.com/albums'),
    headers: <String, String>{
      'Content-Type': 'application/json; charset=UTF-8',
    },
    body: jsonEncode(<String, String>{'title': title}),
  );
}
```

The `http.post()` method returns a `Future` that contains a `Response`.

`http.post()` 方法会返回一个包含 `Response` 的 `Future`。

* [`Future`][] is a core Dart class for working with
  asynchronous operations. A Future object represents a potential
  value or error that will be available at some time in the future.

  [`Future`][] 是 Dart 中用于处理异步操作的核心类。
  Future 对象表示将来某个时刻可用的潜在值或错误。

* The `http.Response` class contains the data received from a successful
  http call.

  `http.Response` 类包含成功的 http 调用所接收到的数据。

* The `createAlbum()` method takes an argument `title`
  that is sent to the server to create an `Album`.

  `createAlbum()` 方法接受参数 `title`，
  该参数会发送到服务器以创建 `Album`。

## 3. Convert the `http.Response` to a custom Dart object

## 3. 将 `http.Response` 转换成自定义的 Dart 对象

While it's easy to make a network request,
working with a raw `Future<http.Response>`
isn't very convenient.  To make your life easier,
convert the `http.Response` into a Dart object.

虽然发起网络请求很容易，
但直接处理原始的 `Future<http.Response>` 并不方便。
为了让后续工作更轻松，
请将 `http.Response` 转换成 Dart 对象。

### Create an Album class

### 创建一个 `Album` 类

First, create an `Album` class that contains
the data from the network request.
It includes a factory constructor that
creates an `Album` from JSON.

首先，创建一个包含网络请求数据的 `Album` 类。
它包含一个工厂构造器，用于从 JSON 创建 `Album`。

Converting JSON with [pattern matching][] is only one option.
For more information, see the full article on
[JSON and serialization][].

使用 [pattern matching][] 转换 JSON 只是其中一种方式。
想了解更多，请查看完整文章：[JSON and serialization][]。

<?code-excerpt "lib/main.dart (Album)"?>
```dart
class Album {
  final int id;
  final String title;

  const Album({required this.id, required this.title});

  factory Album.fromJson(Map<String, dynamic> json) {
    return switch (json) {
      {'id': int id, 'title': String title} => Album(id: id, title: title),
      _ => throw const FormatException('Failed to load album.'),
    };
  }
}
```

### Convert the `http.Response` to an `Album`

### 将 `http.Response` 转换成 `Album`

Use the following steps to update the `createAlbum()`
function to return a `Future<Album>`:

按以下步骤更新 `createAlbum()` 函数，
使其返回 `Future<Album>`：

  1. Convert the response body into a JSON `Map` with the
     `dart:convert` package.

     使用 `dart:convert` package 将响应体转换成 JSON `Map`。

  2. If the server returns a `CREATED` response with a status
     code of 201, then convert the JSON `Map` into an `Album`
     using the `fromJson()` factory method.

     如果服务器返回状态码为 201 的 `CREATED` 响应，
     则使用 `fromJson()` 工厂方法将 JSON `Map` 转换成 `Album`。

  3. If the server doesn't return a `CREATED` response with a
     status code of 201, then throw an exception.
     (Even in the case of a "404 Not Found" server response,
     throw an exception. Do not return `null`.
     This is important when examining
     the data in `snapshot`, as shown below.)

     如果服务器没有返回状态码为 201 的 `CREATED` 响应，则抛出异常。
     （即使是「404 Not Found」的服务器响应，也要抛出异常。不要返回 `null`。
     在检查如下所示的 `snapshot` 中的数据时，这一点很重要。）

<?code-excerpt "lib/main.dart (createAlbum)"?>
```dart
Future<Album> createAlbum(String title) async {
  final response = await http.post(
    Uri.parse('https://jsonplaceholder.typicode.com/albums'),
    headers: <String, String>{
      'Content-Type': 'application/json; charset=UTF-8',
    },
    body: jsonEncode(<String, String>{'title': title}),
  );

  if (response.statusCode == 201) {
    // If the server did return a 201 CREATED response,
    // then parse the JSON.
    return Album.fromJson(jsonDecode(response.body) as Map<String, dynamic>);
  } else {
    // If the server did not return a 201 CREATED response,
    // then throw an exception.
    throw Exception('Failed to create album.');
  }
}
```

Hooray! Now you've got a function that sends the title to a
server to create an album.

太棒了！现在你就拥有了一个将标题发送到服务器以创建相册的函数。

## 4. Get a title from user input

## 4. 从用户输入获取标题

Next, create a `TextField` to enter a title and
a `ElevatedButton` to send data to server.
Also define a `TextEditingController` to read the
user input from a `TextField`.

接下来，创建一个用于输入标题的 `TextField` 和一个用于向服务器发送数据的 `ElevatedButton`。
还要定义一个 `TextEditingController`，
用于从 `TextField` 读取用户输入。

When the `ElevatedButton` is pressed, the `_futureAlbum`
is set to the value returned by `createAlbum()` method.

当按下 `ElevatedButton` 时，
`_futureAlbum` 会被设置为 `createAlbum()` 方法返回的值。

<?code-excerpt "lib/main.dart (Column)" replace="/^return //g;/^\);$/)/g"?>
```dart
Column(
  mainAxisAlignment: MainAxisAlignment.center,
  children: <Widget>[
    TextField(
      controller: _controller,
      decoration: const InputDecoration(hintText: 'Enter Title'),
    ),
    ElevatedButton(
      onPressed: () {
        setState(() {
          _futureAlbum = createAlbum(_controller.text);
        });
      },
      child: const Text('Create Data'),
    ),
  ],
)
```

On pressing the **Create Data** button, make the network request,
which sends the data in the `TextField` to the server
as a `POST` request.
The Future, `_futureAlbum`, is used in the next step.

按下 **Create Data** 按钮后，发起网络请求，
以 `POST` 请求将 `TextField` 中的数据发送到服务器。
下一步会使用 Future `_futureAlbum`。

## 5. Display the response on screen

## 5. 在屏幕上显示响应

To display the data on screen, use the
[`FutureBuilder`][] widget.
The `FutureBuilder` widget comes with Flutter and
makes it easy to work with asynchronous data sources.
You must provide two parameters:

要在屏幕上显示数据，请使用 [`FutureBuilder`][] widget。
`FutureBuilder` widget 随 Flutter 提供，
可让你轻松处理异步数据源。
你必须提供两个参数：

  1. The `Future` you want to work with. In this case,
     the future returned from the `createAlbum()` function.

     你想要处理的 `Future`。在本例中，
     即 `createAlbum()` 函数返回的 future。

  2. A `builder` function that tells Flutter what to render,
     depending on the state of the `Future`: loading,
     success, or error.

     一个 `builder` 函数，根据 `Future` 的状态（loading、success 或 error）
     告诉 Flutter 渲染什么内容。

Note that `snapshot.hasData` only returns `true` when
the snapshot contains a non-null data value.
This is why the `createAlbum()` function should throw an exception
even in the case of a "404 Not Found" server response.
If `createAlbum()` returns `null`, then
`CircularProgressIndicator` displays indefinitely.

请注意，只有当快照包含非空数据值时，
`snapshot.hasData` 才会返回 `true`。
因此，即使在「404 Not Found」的服务器响应情况下，
`createAlbum()` 函数也应抛出异常。
如果 `createAlbum()` 返回 `null`，
则 `CircularProgressIndicator` 会无限期显示。

<?code-excerpt "lib/main.dart (FutureBuilder)" replace="/^return //g;/^\);$/)/g"?>
```dart
FutureBuilder<Album>(
  future: _futureAlbum,
  builder: (context, snapshot) {
    if (snapshot.hasData) {
      return Text(snapshot.data!.title);
    } else if (snapshot.hasError) {
      return Text('${snapshot.error}');
    }

    return const CircularProgressIndicator();
  },
)
```

## Complete example

## 完整样例

<?code-excerpt "lib/main.dart"?>
```dart
import 'dart:async';
import 'dart:convert';

import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;

Future<Album> createAlbum(String title) async {
  final response = await http.post(
    Uri.parse('https://jsonplaceholder.typicode.com/albums'),
    headers: <String, String>{
      'Content-Type': 'application/json; charset=UTF-8',
    },
    body: jsonEncode(<String, String>{'title': title}),
  );

  if (response.statusCode == 201) {
    // If the server did return a 201 CREATED response,
    // then parse the JSON.
    return Album.fromJson(jsonDecode(response.body) as Map<String, dynamic>);
  } else {
    // If the server did not return a 201 CREATED response,
    // then throw an exception.
    throw Exception('Failed to create album.');
  }
}

class Album {
  final int id;
  final String title;

  const Album({required this.id, required this.title});

  factory Album.fromJson(Map<String, dynamic> json) {
    return switch (json) {
      {'id': int id, 'title': String title} => Album(id: id, title: title),
      _ => throw const FormatException('Failed to load album.'),
    };
  }
}

void main() {
  runApp(const MyApp());
}

class MyApp extends StatefulWidget {
  const MyApp({super.key});

  @override
  State<MyApp> createState() {
    return _MyAppState();
  }
}

class _MyAppState extends State<MyApp> {
  final TextEditingController _controller = TextEditingController();
  Future<Album>? _futureAlbum;

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Create Data Example',
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
      ),
      home: Scaffold(
        appBar: AppBar(title: const Text('Create Data Example')),
        body: Container(
          alignment: Alignment.center,
          padding: const EdgeInsets.all(8),
          child: (_futureAlbum == null) ? buildColumn() : buildFutureBuilder(),
        ),
      ),
    );
  }

  Column buildColumn() {
    return Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: <Widget>[
        TextField(
          controller: _controller,
          decoration: const InputDecoration(hintText: 'Enter Title'),
        ),
        ElevatedButton(
          onPressed: () {
            setState(() {
              _futureAlbum = createAlbum(_controller.text);
            });
          },
          child: const Text('Create Data'),
        ),
      ],
    );
  }

  FutureBuilder<Album> buildFutureBuilder() {
    return FutureBuilder<Album>(
      future: _futureAlbum,
      builder: (context, snapshot) {
        if (snapshot.hasData) {
          return Text(snapshot.data!.title);
        } else if (snapshot.hasError) {
          return Text('${snapshot.error}');
        }

        return const CircularProgressIndicator();
      },
    );
  }
}
```

[ConnectionState]: https://api.flutter-io.cn/flutter/widgets/ConnectionState-class.html
[`didChangeDependencies()`]: https://api.flutter-io.cn/flutter/widgets/State/didChangeDependencies.html
[Fetch Data]: /cookbook/networking/fetch-data
[`Future`]: https://api.flutter-io.cn/flutter/dart-async/Future-class.html
[`FutureBuilder`]: https://api.flutter-io.cn/flutter/widgets/FutureBuilder-class.html
[`http`]: https://pub-web.flutter-io.cn/packages/http
[`http.post()`]: https://pub-web.flutter-io.cn/documentation/http/latest/http/post.html
[`http` package]: https://pub-web.flutter-io.cn/packages/http/install
[`InheritedWidget`]: https://api.flutter-io.cn/flutter/widgets/InheritedWidget-class.html
[Introduction to unit testing]: /cookbook/testing/unit/introduction
[`initState()`]: https://api.flutter-io.cn/flutter/widgets/State/initState.html
[JSONPlaceholder]: https://jsonplaceholder.typicode.com/
[JSON and serialization]: /data-and-backend/serialization/json
[Mock dependencies using Mockito]: /cookbook/testing/unit/mocking
[pattern matching]: https://dart.cn/language/patterns
[`State`]: https://api.flutter-io.cn/flutter/widgets/State-class.html