flutter - Dart FormatException:意外字符(在字符1处)

Question

我将JSON解析为来自http库方法get的对象时发现了问题

这是回应机构

{"totalReviews": 0,"averageReviewScore": null,"totalReviewScore": 0,"totalFullScore": 0,"lowestScore": null,"highestScore": null,"reviews": []}

    try {
      final response =
          await http.get(httpConst.DOMAIN + httpConst.MY_HISTORY, headers: {
        'Authorization': '$tokenType $accessToken',
        'Content-Type': 'application/json'
      });
      if (response.statusCode == 200) {
        return MyHistory.fromJson(json.decode(response.body));
      } else {
        print(response.statusCode);
        throw Exception('Failed to get review list');
      }
    } catch (e) {
      final log = Map<String, dynamic>.from(json.decode(e.toString()));
      print('err: ${log.toString()}');
      throw Exception('Failed to get review list');
    }

Answer 1

请解析以下类和命令

Payload payload = payloadFromJson(response);

程式码片段

String response = '{"totalReviews": 0,"averageReviewScore": null,"totalReviewScore": 0,"totalFullScore": 0,"lowestScore": null,"highestScore": null,"reviews": []}';
Payload payload = payloadFromJson(response);
print(payload.totalReviews);

相关的有效载荷类别

// To parse this JSON data, do
//
//     final payload = payloadFromJson(jsonString);

import 'dart:convert';

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

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

class Payload {
    int totalReviews;
    dynamic averageReviewScore;
    int totalReviewScore;
    int totalFullScore;
    dynamic lowestScore;
    dynamic highestScore;
    List<dynamic> reviews;

    Payload({
        this.totalReviews,
        this.averageReviewScore,
        this.totalReviewScore,
        this.totalFullScore,
        this.lowestScore,
        this.highestScore,
        this.reviews,
    });

    factory Payload.fromJson(Map<String, dynamic> json) => Payload(
        totalReviews: json["totalReviews"] == null ? null : json["totalReviews"],
        averageReviewScore: json["averageReviewScore"],
        totalReviewScore: json["totalReviewScore"] == null ? null : json["totalReviewScore"],
        totalFullScore: json["totalFullScore"] == null ? null : json["totalFullScore"],
        lowestScore: json["lowestScore"],
        highestScore: json["highestScore"],
        reviews: json["reviews"] == null ? null : List<dynamic>.from(json["reviews"].map((x) => x)),
    );

    Map<String, dynamic> toJson() => {
        "totalReviews": totalReviews == null ? null : totalReviews,
        "averageReviewScore": averageReviewScore,
        "totalReviewScore": totalReviewScore == null ? null : totalReviewScore,
        "totalFullScore": totalFullScore == null ? null : totalFullScore,
        "lowestScore": lowestScore,
        "highestScore": highestScore,
        "reviews": reviews == null ? null : List<dynamic>.from(reviews.map((x) => x)),
    };
}

完整的代码

import 'package:flutter/material.dart';
// To parse this JSON data, do
//
//     final payload = payloadFromJson(jsonString);

import 'dart:convert';

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

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

class Payload {
  int totalReviews;
  dynamic averageReviewScore;
  int totalReviewScore;
  int totalFullScore;
  dynamic lowestScore;
  dynamic highestScore;
  List<dynamic> reviews;

  Payload({
    this.totalReviews,
    this.averageReviewScore,
    this.totalReviewScore,
    this.totalFullScore,
    this.lowestScore,
    this.highestScore,
    this.reviews,
  });

  factory Payload.fromJson(Map<String, dynamic> json) => Payload(
    totalReviews: json["totalReviews"] == null ? null : json["totalReviews"],
    averageReviewScore: json["averageReviewScore"],
    totalReviewScore: json["totalReviewScore"] == null ? null : json["totalReviewScore"],
    totalFullScore: json["totalFullScore"] == null ? null : json["totalFullScore"],
    lowestScore: json["lowestScore"],
    highestScore: json["highestScore"],
    reviews: json["reviews"] == null ? null : List<dynamic>.from(json["reviews"].map((x) => x)),
  );

  Map<String, dynamic> toJson() => {
    "totalReviews": totalReviews == null ? null : totalReviews,
    "averageReviewScore": averageReviewScore,
    "totalReviewScore": totalReviewScore == null ? null : totalReviewScore,
    "totalFullScore": totalFullScore == null ? null : totalFullScore,
    "lowestScore": lowestScore,
    "highestScore": highestScore,
    "reviews": reviews == null ? null : List<dynamic>.from(reviews.map((x) => x)),
  };
}


void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        // This is the theme of your application.
        //
        // Try running your application with "flutter run". You'll see the
        // application has a blue toolbar. Then, without quitting the app, try
        // changing the primarySwatch below to Colors.green and then invoke
        // "hot reload" (press "r" in the console where you ran "flutter run",
        // or simply save your changes to "hot reload" in a Flutter IDE).
        // Notice that the counter didn't reset back to zero; the application
        // is not restarted.
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

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

  // This widget is the home page of your application. It is stateful, meaning
  // that it has a State object (defined below) that contains fields that affect
  // how it looks.

  // This class is the configuration for the state. It holds the values (in this
  // case the title) provided by the parent (in this case the App widget) and
  // used by the build method of the State. Fields in a Widget subclass are
  // always marked "final".

  final String title;

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

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


  void _incrementCounter() {
    String response = '{"totalReviews": 0,"averageReviewScore": null,"totalReviewScore": 0,"totalFullScore": 0,"lowestScore": null,"highestScore": null,"reviews": []}';
    Payload payload = payloadFromJson(response);
    print(payload.totalReviews);

    setState(() {
      // This call to setState tells the Flutter framework that something has
      // changed in this State, which causes it to rerun the build method below
      // so that the display can reflect the updated values. If we changed
      // _counter without calling setState(), then the build method would not be
      // called again, and so nothing would appear to happen.
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    // This method is rerun every time setState is called, for instance as done
    // by the _incrementCounter method above.
    //
    // The Flutter framework has been optimized to make rerunning build methods
    // fast, so that you can just rebuild anything that needs updating rather
    // than having to individually change instances of widgets.
    return Scaffold(
      appBar: AppBar(
        // Here we take the value from the MyHomePage object that was created by
        // the App.build method, and use it to set our appbar title.
        title: Text(widget.title),
      ),
      body: Center(
        // Center is a layout widget. It takes a single child and positions it
        // in the middle of the parent.
        child: Column(
          // Column is also a layout widget. It takes a list of children and
          // arranges them vertically. By default, it sizes itself to fit its
          // children horizontally, and tries to be as tall as its parent.
          //
          // Invoke "debug painting" (press "p" in the console, choose the
          // "Toggle Debug Paint" action from the Flutter Inspector in Android
          // Studio, or the "Toggle Debug Paint" command in Visual Studio Code)
          // to see the wireframe for each widget.
          //
          // Column has various properties to control how it sizes itself and
          // how it positions its children. Here we use mainAxisAlignment to
          // center the children vertically; the main axis here is the vertical
          // axis because Columns are vertical (the cross axis would be
          // horizontal).
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.display1,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

您可以看到正确的打印数据