Flutter 網絡和(hé)Http

發起HTTP請(qǐng)求

http支持位于dart:io，所以要創建一個HTTP client， 我們需要添加一個導入：

import 'dart:io';

var httpClient = new HttpClient();

該 client 支持常用(yòng)的HTTP操作(zuò), such as GET, POST, PUT, DELETE.

處理(lǐ)異步

注意，HTTP API 在返回值中使用(yòng)了(le)Dart Futures。 我們建議(yì)使用(yòng)async/await語法來(lái)調用(yòng)API。

網絡調用(yòng)通常遵循如下(xià)步驟：

創建 client.

構造 Uri.

發起請(qǐng)求, 等待請(qǐng)求，同時(shí)您也(yě)可以配置請(qǐng)求headers、 body。

關閉請(qǐng)求, 等待響應.

解碼響應的内容.

Several of these steps use Future based APIs. Sample APIs calls for each step above are: 其中的幾個步驟使用(yòng)基于Future的API。上(shàng)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();

}

有關完整的代碼示例，請(qǐng)參閱下(xià)面的“示例”。

解碼和(hé)編碼JSON

使用(yòng)dart:convert庫可以簡單解碼和(hé)編碼JSON。 有關其他(tā)的JSON文(wén)檔，請(qǐng)參閱JSON和(hé)序列化。

解碼簡單的JSON字符串并将響應解析爲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)簡單的JSON進行編碼，請(qǐng)将簡單值（字符串，布爾值或數字字面量）或包含簡單值的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(xià)示例顯示了(le)如何在Flutter應用(yòng)中對(duì)HTTPS GET請(qǐng)求返回的JSON數據進行解碼

It calls the httpbin.com web service testing API, which then responds with your local IP address. Note that secure networking (HTTPS) is used. 它調用(yòng)httpbin.comWeb service測試API，請(qǐng)注意，使用(yòng)安全網絡請(qǐng)求（HTTPS）

運行flutter create，創建一個新的Flutter應用(yòng).

将lib/main.dart替換爲一下(xià)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 {

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: [

new Text('Your current IP address is:'),

new Text('$_ipAddress.'),

spacer,

new RaisedButton(

onPressed: _getIPAddress,

child: new Text('Get IP address'),

),

],

),

),

);

}

}