Flutter如何从json http响应中获取特定值答案

【问题标题】：Flutter how to get specific value from json http responseFlutter如何从json http响应中获取特定值
【发布时间】：2021-02-04 19:20:26
【问题描述】：

我正在使用此代码将 json 数据上传到我的 nodejs 服务器。

   HttpClient client = new HttpClient();
  var data = createSamplePayment().toJson();
  var request = await client.openUrl('POST', Uri.parse(serverEndpoint + '/paymentrequests'));
  request.headers.set(HttpHeaders.contentTypeHeader, 'APPLICATION/JSON');
  request.write(json.encode(data));
  var response = await request.close();
  String reply = await response.transform(utf8.decoder).join();
  print(reply);

print(reply) 的输出是：

flutter: {"url":"https://paymentrequests/86C0110D","token":"w8SWavZNjOG","id":"C3C4966AF64D8CE194F5E3C"}

但我只想获得“token”价值。我能做些什么来解决这个问题？我尝试了许多不同的方法，但都没有成功。

【问题讨论】：

标签： json flutter dart

【解决方案1】：

class DetailsModel {
  String url;
  String token;
  String id;

  DetailsModel({this.url, this.token, this.id});

  DetailsModel.fromJson(Map<String, dynamic> json) {
    url = json['url'];
    token = json['token'];
    id = json['id'];
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    data['url'] = this.url;
    data['token'] = this.token;
    data['id'] = this.id;
    return data;
  }
}

首先，将您的响应转换为模型，为此您需要上述代码。然后映射您的响应。

DetailsModel details = DetailsModel.fromJson(response);

然后访问您可以简单使用的详细信息。

dynamic token = details.token; 
print(token); // w8SWavZNjOG

【讨论】：

好的，现在我得到这个错误：参数类型'HttpClientResponse'不能分配给参数类型'Map'。",
是的，这是因为您无法为其分配 HttpClient 响应。就这样做吧。 final Map response1 = json.decode(reply); 然后将 response1 传递给 fromJson 方法，而不是响应。
好吧。我应该把它放在哪里？而不是 DetailsModel details = DetailsModel.fromJson(response);?
是的，DetailsModel details = DetailsModel.fromJson(reply)
它看起来不起作用，因为回复是一个字符串

【解决方案2】：

您可以在下面复制粘贴运行完整代码
我使用下面的代码来模拟这种情况
你可以做payloadFromJson(reply) 和return payload.token
你可以参考Payload类的完整代码
代码sn-p

Payload payloadFromJson(String str) => Payload.fromJson(json.decode(str));
...
Future<String> postWithClientCertificate() async {
    ...
    Payload payload = payloadFromJson(reply);
    print(payload.token);
    return payload.token;
  }

输出

I/flutter ( 5995): w8SWavZNjOG
I/flutter ( 5995): token w8SWavZNjOG

完整代码

import 'dart:convert';
import 'dart:io';
import 'package:flutter/material.dart';
import 'dart:convert';

Payload payloadFromJson(String str) => Payload.fromJson(json.decode(str));

String payloadToJson(Payload data) => json.encode(data.toJson());

class Payload {
  Payload({
    this.url,
    this.token,
    this.id,
  });

  String url;
  String token;
  String id;

  factory Payload.fromJson(Map<String, dynamic> json) => Payload(
        url: json["url"],
        token: json["token"],
        id: json["id"],
      );

  Map<String, dynamic> toJson() => {
        "url": url,
        "token": token,
        "id": id,
      };
}

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  void _incrementCounter() async{
    String token = await postWithClientCertificate();
    print("token $token");

    setState(() {
      _counter++;
    });
  }

  Future<String> postWithClientCertificate() async {
    /*final serverEndpoint = 'https://1991269db78887f9e.ngrok.io';
    HttpClient client = new HttpClient();
    var data = createSamplePayment().toJson();
    var request = await client.openUrl('POST', Uri.parse(serverEndpoint + '/paymentrequests'));
    request.headers.set(HttpHeaders.contentTypeHeader, 'APPLICATION/JSON');
    request.write(json.encode(data));
    var response = await request.close();
    String reply = await response.transform(utf8.decoder).join();
    print(reply);*/

    String reply =
        '''{"url":"https://paymentrequests/86C0110D","token":"w8SWavZNjOG","id":"C3C4966AF64D8CE194F5E3C"}''';

    Payload payload = payloadFromJson(reply);

    print(payload.token);
    return payload.token;
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.headline4,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ),
    );
  }
}

【讨论】：