Flutter 網(wǎng)絡(luò)和Http

發(fā)起HTTP請(qǐng)求

http支持位于dart:io，所以要?jiǎng)?chuàng)建一個(gè)HTTP client， 我們需要添加一個(gè)導(dǎo)入：

import 'dart:io';

var httpClient = new HttpClient();

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

處理異步

注意，HTTP API 在返回值中使用了Dart Futures。 我們建議使用async/await語(yǔ)法來調(diào)用API。

網(wǎng)絡(luò)調(diào)用通常遵循如下步驟：

1. 創(chuàng)建 client.
2. 構(gòu)造 Uri.
3. 發(fā)起請(qǐng)求, 等待請(qǐng)求，同時(shí)您也可以配置請(qǐng)求headers、 body。
4. 關(guān)閉請(qǐng)求, 等待響應(yīng).
5. 解碼響應(yīng)的內(nèi)容.

Several of these steps use Future based APIs. Sample APIs calls for each step above are: 其中的幾個(gè)步驟使用基于Future的API。上面步驟的示例：

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();
}

有關(guān)完整的代碼示例，請(qǐng)參閱下面的“示例”。

解碼和編碼JSON

使用dart:convert庫(kù)可以簡(jiǎn)單解碼和編碼JSON。 有關(guān)其他的JSON文檔，請(qǐng)參閱JSON和序列化。

解碼簡(jiǎn)單的JSON字符串并將響應(yīng)解析為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

要對(duì)簡(jiǎn)單的JSON進(jìn)行編碼，請(qǐng)將簡(jiǎn)單值（字符串，布爾值或數(shù)字字面量）或包含簡(jiǎn)單值的Map，list等傳給encode方法：

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

示例: 解碼 HTTPS GET請(qǐng)求的JSON

以下示例顯示了如何在Flutter應(yīng)用中對(duì)HTTPS GET請(qǐng)求返回的JSON數(shù)據(jù)進(jìn)行解碼

It calls the httpbin.com web service testing API, which then responds with your local IP address. Note that secure networking (HTTPS) is used. 它調(diào)用httpbin.comWeb service測(cè)試API，請(qǐng)注意，使用安全網(wǎng)絡(luò)請(qǐng)求（HTTPS）

1. 運(yùn)行flutter create，創(chuàng)建一個(gè)新的Flutter應(yīng)用.
2. 將lib/main.dart替換為一下內(nèi)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:\nHttp 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 文檔

有關(guān)完整的API文檔，請(qǐng)參閱:

• 庫(kù)dart:io
• 庫(kù)dart:convert