json - 在Flutter/Dart中解析JSON:<RK，RV>()=> Map <RK，RV>，NoSuchMethodError-(数组问题？)-6ren

json - 在Flutter/Dart中解析JSON:()=> Map ，NoSuchMethodError-(数组问题？)

转载作者：行者123 更新时间：2023-12-03 03:00:36

我对Flutter / Dart还是有点陌生，而Ive在相当长的一段时间内一直在努力解析JSON。对我来说，这似乎是一项艰巨的任务，尽管我认为我的JSON结构并不那么复杂。

您的帮助将不胜感激。

这是我要解析的JSON:

{
   "predictionICL":{
      "openingTimeToday":"8:00 - 23:00",
      "openingTimeTomorrow":"8:00 - 23:00",
      "percentagesToday":[
         3,
         5,
         11,
         17,
         20,
         23,
         25,
         26,
         25,
         29,
         30,
         32,
         31,
         35,
         40,
         43,
         44,
         46,
         49,
         53,
         50,
         56,
         54,
         60,
         62,
         61,
         69,
         70,
         75,
         76,
         84,
         90,
         94,
         100,
         93,
         81,
         72,
         70,
         73,
         71,
         63,
         59,
         55,
         56,
         51,
         49,
         50,
         45,
         43,
         40,
         38,
         35,
         31,
         27,
         25,
         23,
         20,
         20,
         19,
         17,
         12,
         9,
         8,
         2,
         1
      ],
      "percentagesTomorrow":[ 
         0,
         0,
         1,
         7,
         14,
         20,
         22,
         21,
         21,
         22,
         20,
         25,
         27,
         31,
         30,
         31,
         32,
         33,
         30,
         34,
         35,
         33,
         35,
         37,
         39,
         40,
         40,
         39,
         38,
         40,
         41,
         38,
         34,
         37,
         34,
         35,
         33,
         32,
         31,
         30,
         33,
         30,
         31,
         30,
         29,
         30,
         27,
         28,
         26,
         23,
         20,
         19,
         16,
         17,
         15,
         12,
         10,
         7,
         5,
         1,
         1,
         0,
         0,
         0,
         0
      ]
   },
   "predictionRandwyck":{
      "openingTimeToday":"8:00 - 23:00",
      "openingTimeTomorrow":"8:00 - 23:00",
      "percentagesToday":[
         3,
         5,
         11,
         17,
         20,
         23,
         25,
         26,
         25,
         29,
         30,
         32,
         31,
         35,
         40,
         43,
         44,
         46,
         49,
         53,
         50,
         56,
         54,
         60,
         62,
         61,
         69,
         70,
         75,
         76,
         84,
         90,
         94,
         100,
         93,
         81,
         72,
         70,
         73,
         71,
         63,
         59,
         55,
         56,
         51,
         49,
         50,
         45,
         43,
         40,
         38,
         35,
         31,
         27,
         25,
         23,
         20,
         20,
         19,
         17,
         12,
         9,
         8,
         2,
         1
      ],
      "percentagesTomorrow":[
         0,
         0,
         1,
         7,
         14,
         20,
         22,
         21,
         21,
         22,
         20,
         25,
         27,
         31,
         30,
         31,
         32,
         33,
         30,
         34,
         35,
         33,
         35,
         37,
         39,
         40,
         40,
         39,
         38,
         40,
         41,
         38,
         34,
         37,
         34,
         35,
         33,
         32,
         31,
         30,
         33,
         30,
         31,
         30,
         29,
         30,
         27,
         28,
         26,
         23,
         20,
         19,
         16,
         17,
         15,
         12,
         10,
         7,
         5,
         1,
         1,
         0,
         0,
         0,
         0
      ]
   },
   "predictionTapijn":{
      "openingTimeToday":"8:00 - 23:00",
      "openingTimeTomorrow":"8:00 - 23:00",
      "percentagesToday":[
         3,
         5,
         11,
         17,
         20,
         23,
         25,
         26,
         25,
         29,
         30,
         32,
         31,
         35,
         40,
         43,
         44,
         46,
         49,
         53,
         50,
         56,
         54,
         60,
         62,
         61,
         69,
         70,
         75,
         76,
         84,
         90,
         94,
         100,
         93,
         81,
         72,
         70,
         73,
         71,
         63,
         59,
         55,
         56,
         51,
         49,
         50,
         45,
         43,
         40,
         38,
         35,
         31,
         27,
         25,
         23,
         20,
         20,
         19,
         17,
         12,
         9,
         8,
         2,
         1
      ],
      "percentagesTomorrow":[
         0,
         0,
         1,
         7,
         14,
         20,
         22,
         21,
         21,
         22,
         20,
         25,
         27,
         31,
         30,
         31,
         32,
         33,
         30,
         34,
         35,
         33,
         35,
         37,
         39,
         40,
         40,
         39,
         38,
         40,
         41,
         38,
         34,
         37,
         34,
         35,
         33,
         32,
         31,
         30,
         33,
         30,
         31,
         30,
         29,
         30,
         27,
         28,
         26,
         23,
         20,
         19,
         16,
         17,
         15,
         12,
         10,
         7,
         5,
         1,
         1,
         0,
         0,
         0,
         0
      ]
   },
   "message":"optionalmessageString"
}

它基本上只是数据类型LibraryPrediction的三个实例和一个可选的Message字符串。

数据类型LibraryPrediction由一个字符串“openingTimeToday”，一个字符串“openingTimeTomorrow”和两个 double 数组“percentagesToday”和“percentagesTomorrow”组成。

现在，由于服务器尚未运行，我正在尝试从磁盘上方解析json。
到目前为止，这是我的代码:

我有一个服务文件:

import 'dart:convert';
import 'package:flutter/services.dart';
import 'package:test_app/models/predictions_update_model.dart';


PredictionsUpdate parseUpdate(String responseBody) {
  final jsonResponse = json.decode(responseBody).cast<Map<String, dynamic>>();

  PredictionsUpdate update = jsonResponse.map<PredictionsUpdate>((json) => PredictionsUpdate.fromJson(json));

  return update;

}

Future<PredictionsUpdate> fetchUpdate() async {

  final response = await rootBundle.loadString('lib/testJson/data.json');

  return parseUpdate(response);
}

还有一个模型文件:

class PredictionsUpdate {
  final LibraryPrediction predictionICL;
  final LibraryPrediction predictionRandwyck;
  final LibraryPrediction predictionTapijn;
  final String message;

  PredictionsUpdate({
    this.predictionICL,
    this.predictionRandwyck,
    this.predictionTapijn,
    this.message,
});

  factory PredictionsUpdate.fromJson(Map<String, dynamic> parsedJson){
    return PredictionsUpdate(
      predictionICL: LibraryPrediction.fromJson(parsedJson['predictionICL']),
      predictionRandwyck: LibraryPrediction.fromJson(parsedJson['predictionRandwyck']),
      predictionTapijn: LibraryPrediction.fromJson(parsedJson['predictionTapijn']),
      message: parsedJson['message'] as String,
    );
  }
}

class LibraryPrediction {
  final String openingTimeToday;
  final String openingTimeTomorrow;
  final List<double> percentagesToday;
  final List<double> percentagesTomorrow;

  LibraryPrediction({
    this.openingTimeToday,
    this.openingTimeTomorrow,
    this.percentagesToday,
    this.percentagesTomorrow,
  });

  factory LibraryPrediction.fromJson(Map<String, dynamic> json){
    return LibraryPrediction(
      openingTimeToday: json['openingTimeToday'] as String,
      openingTimeTomorrow: json['openingTimeTomorrow'] as String,
      percentagesToday: json['percentagesToday'] as List<double>,
      percentagesTomorrow: json['percentagesTomorrow'] as List<double>,
    );
  }
}

这就是我所谓的函数:


Row(
              children: <Widget>[
                 RaisedButton(
                  child: Text('update'),
                  onPressed: () {
                    Future<PredictionsUpdate> futureUpdate = fetchUpdate();
                    futureUpdate.then((update)=> widget.currentNumbers = update)
                        .catchError((error) => print(error));
                  },
                ),
              ],
            ),

每当我尝试解析JSON时，都会出现以下错误:

flutter: NoSuchMethodError: Class '_InternalLinkedHashMap<String, dynamic>' has no instance method 'cast' with matching arguments.
Receiver: _LinkedHashMap len:4
Tried calling: cast<Map<String, dynamic>>()
Found: cast<RK, RV>() => Map<RK, RV>

我有种感觉，当我尝试解析“percentagesToday”或“percentagesTomorrow” double 数组时，该错误起源于某个地方，但是我不能肯定地说，我无法从错误消息中获取更多线索。

我非常感谢您找出我出了问题的地方。

最佳答案

您可以在下面复制粘贴运行完整代码
你可以这样List<double>.from(json["percentagesToday"].map((x) => x.toDouble())),
程式码片段

factory LibraryPrediction.fromJson(Map<String, dynamic> json) =>
      LibraryPrediction(
        openingTimeToday: json["openingTimeToday"],
        openingTimeTomorrow: json["openingTimeTomorrow"],
        percentagesToday: List<double>.from(
            json["percentagesToday"].map((x) => x.toDouble())),
        percentagesTomorrow: List<double>.from(
            json["percentagesTomorrow"].map((x) => x.toDouble())),
      );
...   
futureUpdate.then((update) {
  print('${update.predictionIcl.openingTimeToday.toString()}');
  print('${update.message}');
  print('${update.predictionRandwyck.openingTimeTomorrow}');
}).catchError((error) => print(error));

输出

I/flutter ( 7344): 8:00 - 23:00
I/flutter ( 7344): optionalmessageString
I/flutter ( 7344): 8:00 - 23:00

完整的代码

import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
import 'dart:convert';

PredictionsUpdate predictionsUpdateFromJson(String str) =>
    PredictionsUpdate.fromJson(json.decode(str));

class PredictionsUpdate {
  LibraryPrediction predictionIcl;
  LibraryPrediction predictionRandwyck;
  LibraryPrediction predictionTapijn;
  String message;

  PredictionsUpdate({
    this.predictionIcl,
    this.predictionRandwyck,
    this.predictionTapijn,
    this.message,
  });

  factory PredictionsUpdate.fromJson(Map<String, dynamic> json) =>
      PredictionsUpdate(
        predictionIcl: LibraryPrediction.fromJson(json["predictionICL"]),
        predictionRandwyck:
            LibraryPrediction.fromJson(json["predictionRandwyck"]),
        predictionTapijn: LibraryPrediction.fromJson(json["predictionTapijn"]),
        message: json["message"],
      );
}

class LibraryPrediction {
  String openingTimeToday;
  String openingTimeTomorrow;
  List<double> percentagesToday;
  List<double> percentagesTomorrow;

  LibraryPrediction({
    this.openingTimeToday,
    this.openingTimeTomorrow,
    this.percentagesToday,
    this.percentagesTomorrow,
  });

  factory LibraryPrediction.fromJson(Map<String, dynamic> json) =>
      LibraryPrediction(
        openingTimeToday: json["openingTimeToday"],
        openingTimeTomorrow: json["openingTimeTomorrow"],
        percentagesToday: List<double>.from(
            json["percentagesToday"].map((x) => x.toDouble())),
        percentagesTomorrow: List<double>.from(
            json["percentagesTomorrow"].map((x) => x.toDouble())),
      );
}

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      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;

  Future<PredictionsUpdate> fetchUpdate() async {
    String jsonString = '''
    {
   "predictionICL":{
      "openingTimeToday":"8:00 - 23:00",
      "openingTimeTomorrow":"8:00 - 23:00",
      "percentagesToday":[
         3,
         5,
         11,
         17,
         20,
         23,
         25,
         26,
         25,
         29,
         30,
         32,
         31,
         35,
         40,
         43,
         44,
         46,
         49,
         53,
         50,
         56,
         54,
         60,
         62,
         61,
         69,
         70,
         75,
         76,
         84,
         90,
         94,
         100,
         93,
         81,
         72,
         70,
         73,
         71,
         63,
         59,
         55,
         56,
         51,
         49,
         50,
         45,
         43,
         40,
         38,
         35,
         31,
         27,
         25,
         23,
         20,
         20,
         19,
         17,
         12,
         9,
         8,
         2,
         1
      ],
      "percentagesTomorrow":[ 
         0,
         0,
         1,
         7,
         14,
         20,
         22,
         21,
         21,
         22,
         20,
         25,
         27,
         31,
         30,
         31,
         32,
         33,
         30,
         34,
         35,
         33,
         35,
         37,
         39,
         40,
         40,
         39,
         38,
         40,
         41,
         38,
         34,
         37,
         34,
         35,
         33,
         32,
         31,
         30,
         33,
         30,
         31,
         30,
         29,
         30,
         27,
         28,
         26,
         23,
         20,
         19,
         16,
         17,
         15,
         12,
         10,
         7,
         5,
         1,
         1,
         0,
         0,
         0,
         0
      ]
   },
   "predictionRandwyck":{
      "openingTimeToday":"8:00 - 23:00",
      "openingTimeTomorrow":"8:00 - 23:00",
      "percentagesToday":[
         3,
         5,
         11,
         17,
         20,
         23,
         25,
         26,
         25,
         29,
         30,
         32,
         31,
         35,
         40,
         43,
         44,
         46,
         49,
         53,
         50,
         56,
         54,
         60,
         62,
         61,
         69,
         70,
         75,
         76,
         84,
         90,
         94,
         100,
         93,
         81,
         72,
         70,
         73,
         71,
         63,
         59,
         55,
         56,
         51,
         49,
         50,
         45,
         43,
         40,
         38,
         35,
         31,
         27,
         25,
         23,
         20,
         20,
         19,
         17,
         12,
         9,
         8,
         2,
         1
      ],
      "percentagesTomorrow":[
         0,
         0,
         1,
         7,
         14,
         20,
         22,
         21,
         21,
         22,
         20,
         25,
         27,
         31,
         30,
         31,
         32,
         33,
         30,
         34,
         35,
         33,
         35,
         37,
         39,
         40,
         40,
         39,
         38,
         40,
         41,
         38,
         34,
         37,
         34,
         35,
         33,
         32,
         31,
         30,
         33,
         30,
         31,
         30,
         29,
         30,
         27,
         28,
         26,
         23,
         20,
         19,
         16,
         17,
         15,
         12,
         10,
         7,
         5,
         1,
         1,
         0,
         0,
         0,
         0
      ]
   },
   "predictionTapijn":{
      "openingTimeToday":"8:00 - 23:00",
      "openingTimeTomorrow":"8:00 - 23:00",
      "percentagesToday":[
         3,
         5,
         11,
         17,
         20,
         23,
         25,
         26,
         25,
         29,
         30,
         32,
         31,
         35,
         40,
         43,
         44,
         46,
         49,
         53,
         50,
         56,
         54,
         60,
         62,
         61,
         69,
         70,
         75,
         76,
         84,
         90,
         94,
         100,
         93,
         81,
         72,
         70,
         73,
         71,
         63,
         59,
         55,
         56,
         51,
         49,
         50,
         45,
         43,
         40,
         38,
         35,
         31,
         27,
         25,
         23,
         20,
         20,
         19,
         17,
         12,
         9,
         8,
         2,
         1
      ],
      "percentagesTomorrow":[
         0,
         0,
         1,
         7,
         14,
         20,
         22,
         21,
         21,
         22,
         20,
         25,
         27,
         31,
         30,
         31,
         32,
         33,
         30,
         34,
         35,
         33,
         35,
         37,
         39,
         40,
         40,
         39,
         38,
         40,
         41,
         38,
         34,
         37,
         34,
         35,
         33,
         32,
         31,
         30,
         33,
         30,
         31,
         30,
         29,
         30,
         27,
         28,
         26,
         23,
         20,
         19,
         16,
         17,
         15,
         12,
         10,
         7,
         5,
         1,
         1,
         0,
         0,
         0,
         0
      ]
   },
   "message":"optionalmessageString"
}
    ''';

    //final response = await rootBundle.loadString('lib/testJson/data.json');
    final http.Response response = http.Response(jsonString, 200);
    PredictionsUpdate payload = predictionsUpdateFromJson(response.body);
    return payload;
  }

  void _incrementCounter() {
    Future<PredictionsUpdate> futureUpdate = fetchUpdate();
    futureUpdate.then((update) {
      print('${update.predictionIcl.openingTimeToday.toString()}');
      print('${update.message}');
      print('${update.predictionRandwyck.openingTimeTomorrow}');
    }).catchError((error) => print(error));

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

  @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),
      ),
    );
  }
}

关于json - 在Flutter/Dart中解析JSON:<RK，RV>()=> Map <RK，RV>，NoSuchMethodError-(数组问题？)，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/61044155/

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java - 基于Spring的应用程序初始化entityManagerFactory失败，NoSuchMethodError
我正在使用 Spring 框架和 Maven 开发 Java Enterprise 应用程序。我正在为此学习一门类(class)，并且一直坚持集成 Hibernate JPA。当我运行项目时，它返回以
android - NoSuchMethodError，迭代器调用为null
I/flutter ( 8282): The following NoSuchMethodError was thrown building Meme(dirty, state: _MemeState
flutter - NoSuchMethodError JSON
运行以下代码时出现 NoSuchMethodError - 我想从 JSON url 打印出轨道标题 - 我错过了什么吗？ import 'dart:async'; import 'dart:conv
android - flutter - NoSuchMethodError
我正在做 Searchview flutter 中的例子 https://github.com/MageshPandian20/Flutter-SearchView 但我想对进行更改子项类有一个最
java - 通过JDBC连接到Hive时出现Java NoSuchMethodError
尝试从Eclipse中的简单Java程序连接到Hive时出现以下错误。看起来好像连接，然后引发此错误。我可以通过beeline在本地连接到Hive Thrift服务器，而不会出现问题。两个libth
spring - 身份验证时Auth0:NoSuchMethodError
当我向安全资源发出请求时，会发生NoSuchMethodError。基于基于Spring Boot 1.4.4的Grails 3.2.5的项目 AppConfig: @EnableWebSecuri
Java - NoSuchMethodError 未被异常捕获
这个问题已经有答案了: Differences between Exception and Error (11 个回答) 已关闭 7 年前。我的印象是 Exception 非常适合捕获所有可能的异常
编译jar时出现java.lang.NoSuchMethodError
祝大家有美好的一天!我使用 google Vision API，当我在 IntelliJ Idea 中运行我的程序时，它工作得很好，但是当我编译 jar 文件时，它在处理照片时给出错误 java.la
本地项目源码包出现java.lang.NoSuchMethodError？
我一直在为这个问题苦苦挣扎。我正在开发一个包含很多包的 netbeans java 项目，起初我更改了 gui，但是当我运行代码时，它没有反射(reflect)任何更改，即使我在保存、清理、清理和编译
java - 即使存在自编码方法也会出现 NoSuchMethodError
我一直在寻找问题的解决方案，但没有得到足够的答案。我正在开发 Bukkit插件的更新系统。因此，我必须自己编写这些类的代码。但我一直想从 debug(String) 调用一个方法(具体来说: ano

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json - 在Flutter/Dart中解析JSON:()=> Map ，NoSuchMethodError-(数组问题？)