Flutter 网络和Http

发起HTTP请求

http支持位于dart:io，所以要创建一个HTTP client， 我们需要添加一个导入：

import 'dart:io';

var httpClient = new HttpClient();

该 client 支持常用的HTTP操作, such as GET, POST, PUT, DELETE.

处理异步

注意，HTTP API 在返回值中使用了Dart Futures。 我们建议使用async/await语法来调用API。

网络调用通常遵循如下步骤：

1. 创建 client.
2. 构造 Uri.
3. 发起请求, 等待请求，同时您也可以配置请求headers、 body。
4. 关闭请求, 等待响应.
5. 解码响应的内容.

Several of these steps use Future based APIs. Sample APIs calls for each step above are: 其中的几个步骤使用基于Future的API。上面步骤的示例：

get() async {
  var httpClient = new HttpClient();
  var uri = new Uri.http(
      'example.com', '/path1/path2', {'param1': '42', 'param2': 'foo'});
  var request = await httpClient.getUrl(uri);
  var response = await request.close();
  var responseBody = await response.transform(UTF8.decoder).join();
}

有关完整的代码示例，请参阅下面的“示例”。

解码和编码JSON

使用dart:convert库可以简单解码和编码JSON。 有关其他的JSON文档，请参阅JSON和序列化。

解码简单的JSON字符串并将响应解析为Map：

Map data = JSON.decode(responseBody);
// Assume the response body is something like: ['foo', { 'bar': 499 }]
int barValue = data[1]['bar']; // barValue is set to 499

要对简单的JSON进行编码，请将简单值（字符串，布尔值或数字字面量）或包含简单值的Map，list等传给encode方法：

String encodedString = JSON.encode([1, 2, { 'a': null }]);

示例: 解码 HTTPS GET请求的JSON

以下示例显示了如何在Flutter应用中对HTTPS GET请求返回的JSON数据进行解码

It calls the httpbin.com web service testing API, which then responds with your local IP address. Note that secure networking (HTTPS) is used. 它调用httpbin.comWeb service测试API，请注意，使用安全网络请求（HTTPS）

1. 运行flutter create，创建一个新的Flutter应用.
2. 将lib/main.dart替换为一下内容:

import 'dart:convert';
import 'dart:io';

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      home: new MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key}) : super(key: key);

  @override
  _MyHomePageState createState() => new _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  var _ipAddress = 'Unknown';

  _getIPAddress() async {
    var url = 'https://httpbin.org/ip';
    var httpClient = new HttpClient();

    String result;
    try {
      var request = await httpClient.getUrl(Uri.parse(url));
      var response = await request.close();
      if (response.statusCode == HttpStatus.OK) {
        var json = await response.transform(utf8.decoder).join();
        var data = jsonDecode(json);
        result = data['origin'];
      } else {
        result =
            'Error getting IP address:
Http status ${response.statusCode}';
      }
    } catch (exception) {
      result = 'Failed getting IP address';
    }

    // If the widget was removed from the tree while the message was in flight,
    // we want to discard the reply rather than calling setState to update our
    // non-existent appearance.
    if (!mounted) return;

    setState(() {
      _ipAddress = result;
    });
  }

  @override
  Widget build(BuildContext context) {
    var spacer = new SizedBox(height: 32.0);

    return new Scaffold(
      body: new Center(
        child: new Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            new Text('Your current IP address is:'),
            new Text('$_ipAddress.'),
            spacer,
            new RaisedButton(
              onPressed: _getIPAddress,
              child: new Text('Get IP address'),
            ),
          ],
        ),
      ),
    );
  }
}

API 文档

有关完整的API文档，请参阅:

• 库dart:io
• 库dart:convert