Flutter：异常：类型'（动态，动态，动态）=> void'不是'f'类型'（字符串，动态）=> void'的子类型

Question

如何将多个 json 对象添加/映射到 dart 对象

import 'dart:async';
import 'dart:convert';

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

Future<List<Photo>> fetchPhotos(http.Client client) async {
  final response =
  await client.get('https://cloud.iexapis.com/stable/stock/market/batch?symbols=SLVO,MONY&types=stats&token=');
  /*String response = '''
 {"AAPL":
   {"stats":{"week52change":0.232986,"week52high":255.93,"week52low":142,"marketcap":1136677331400,"employees":137000,"day200MovingAvg":199.29,"day50MovingAvg":225.28,"float":4436680630.59,"avg10Volume":26482506.4,"avg30Volume":26817874.5,"ttmEPS":11.9342,"ttmDividendRate":3,"companyName":"Apple, Inc."
   }
   },
 "FB":
   {"stats":{"week52change":0.1,"week52high":255.93,"week52low":142,"marketcap":1136677331400,"employees":137000,"day200MovingAvg":199.29,"day50MovingAvg":225.28,"float":4436680630.59,"avg10Volume":26482506.4,"avg30Volume":26817874.5,"ttmEPS":11.9342,"ttmDividendRate":3,"companyName":"Apple, Inc."
   }
   }
}
  ''';*/
  // Use the compute function to run parsePhotos in a separate isolate.
  return compute(parsePhotos, response.body);
}

// A function that converts a response body into a List<Photo>.
List<Photo> parsePhotos(String responseBody) {
 //final parsed = json.decode(responseBody).cast<Map<String,dynamic>>();

  //return parsed.map<Photo>((json) => Photo.fromJson(json)).toList();

  dynamic Obj = json.decode(responseBody);
  print(Obj.length);
  List<Photo> photoList = [];
  Obj.forEach((k, v,z) => photoList.add(Photo(k,v,z)));

  return photoList;
}

class Photo {
  String symbol;
   String companyName;
  dynamic stats;
  //dynamic stats;
  Photo(this.symbol ,this.stats,this.companyName);
}

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final appTitle = 'Isolate Demo';

    return MaterialApp(
      title: appTitle,
      home: MyHomePage(title: appTitle),
    );
  }
}

class MyHomePage extends StatelessWidget {
  final String title;

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(title),
      ),
      body: FutureBuilder<List<Photo>>(
        future: fetchPhotos(http.Client()),
        builder: (context, snapshot) {
          if (snapshot.hasError) print(snapshot.error);

          return snapshot.hasData
              ? PhotosList(photos: snapshot.data)
              : Center(child: CircularProgressIndicator());
        },
      ),
    );
  }
}

class PhotosList extends StatelessWidget {
  final List<Photo> photos;

  PhotosList({Key key, this.photos}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return GridView.builder(
      gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
        crossAxisCount: 2,
      ),
      itemCount: photos.length,
      itemBuilder: (context, index) {
        return ListTile(
          leading: Icon(Icons.album),
           title: Column(  children: [
             Text(photos[index].symbol),
                      Text(photos[index].companyName),
                   ],
                   ),
          subtitle: Column(
            children: [
             // Text( ' ${photos[index].stats["stats"]["dividendYield"]["companyName"]}'),
            //  Text( ' ${photos[index].data["quote"]["iexRealtimePrice"]}' ' ${photos[index].stats["stats"]["dividendYield"]["companyName"]}'),
             // Text( ' ${photos[index].data["quote"]["iexRealtimePrice"]}'),
            Text ( '${photos[index].stats["dividendYield"] ?? ""}'),
            ],
          ),
         //title: Text(photos[index].symbol),
         //subtitle: Text( ' ${photos[index].stats["stats"]["dividendYield"]["companyName"]}'),
          //subtitle: Text( ' ${photos[index].data["quote"]["iexRealtimePrice"]}' ' ${photos[index].stats["stats"]["dividendYield"]["companyName"]}'),
       // subtitle: Text( ' ${photos[index].data["quote"]["iexRealtimePrice"]}'),
         // subtitle: Text ( ' ${photos[index].stats["stats"]["dividendYield"]}'),
        );
      },
    );
  }
}

json

{"SLVO":{"stats":{"week52change":0.047256,"week52high":7.48,"week52low":6.23,"marketcap":null,"employees":null ,"day200MovingAvg":6.88,"day50MovingAvg":7.13,"float":null,"avg10Volume":7454.8,"avg30Volume":7927.83,"ttmEPS":null,"ttmDividendRate":null,"companyName":"Credit Suisse X-Links Silver Shares Covered Call ETN","sharesOutstanding":0,"maxChangePercent":58.7391,"year5ChangePercent":-0.4128,"year2ChangePercent":-0.1369,"year1ChangePercent":0.047256,"ytdChangePercent":-0.005789," month6ChangePercent":0.074445,"month3ChangePercent":-0.035112,"month1ChangePercent":-0.025532,"day30ChangePercent":-0.035112,"day5ChangePercent":-0.007225,"nextDividendDate":null,"dividendYield":null,"nextEarningsDate":null ,"exDividendDate":null,"peRatio":null,"beta":-0.06347545711182472},"quote":{"symbol":"SLVO","companyName":"Credit Suisse X-链接 Silver Shares Covered Call ETN","primaryExchange":"NASDAQ","calculationPrice":"close","open":6.89,"openTime":1574346600589,"cl ose":6.88,"closeTime":1574370000242,"high":6.9,"low":6.87,"latestPrice":6.88,"latestSource":"Close","latestTime":"11 月 21 日，

添加： &types=stats,quote&token

错误

I/flutter (28411)：异常：类型 '(dynamic, dynamic, dynamic) => void' 不是类型 '(String, dynamic) => void' of 'f' 的子类型 我/颤振（28411）：71 I/flutter (28411): 异常：类型 '(dynamic, dynamic, dynamic) => void' 不是类型 '(String, dynamic) => void' of 'f' 的子类型

Answer 1

我已修改 url 以包含统计信息和报价
你不能用两个动态，它的for map
你还需要动态字段名
您可以添加令牌并使用完整代码运行，演示图片如下
代码sn-p

 Text ( '${photos[index].data["stats"]["dividendYield"] ?? ""}'),
 Text ( '${photos[index].data["stats"]["week52change"] ?? ""}'),
 Text ( '${photos[index].data["quote"]["companyName"] ?? ""}'),

演示

完整代码

import 'dart:async';
import 'dart:convert';

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

Future<List<Photo>> fetchPhotos(http.Client client) async {
  final response =
  await client.get('https://cloud.iexapis.com/stable/stock/market/batch?symbols=SLVO,MONY&types=stats,quote&token=');

  // Use the compute function to run parsePhotos in a separate isolate.
  return compute(parsePhotos, response.body);
}

// A function that converts a response body into a List<Photo>.
List<Photo> parsePhotos(String responseBody) {
  //final parsed = json.decode(responseBody).cast<Map<String,dynamic>>();

  //return parsed.map<Photo>((json) => Photo.fromJson(json)).toList();

  dynamic Obj = json.decode(responseBody);
  print(responseBody);
  print(Obj.length);

  List<Photo> photoList = [];
  Obj.forEach((k, v) => photoList.add(Photo(k,v)));

  return photoList;
}

class Photo {
  String symbol;
  //String companyName;
  dynamic data;
  //dynamic quote;
  Photo(this.symbol ,this.data);
}

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final appTitle = 'Isolate Demo';

    return MaterialApp(
      title: appTitle,
      home: MyHomePage(title: appTitle),
    );
  }
}

class MyHomePage extends StatelessWidget {
  final String title;

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(title),
      ),
      body: FutureBuilder<List<Photo>>(
        future: fetchPhotos(http.Client()),
        builder: (context, snapshot) {
          if (snapshot.hasError) print(snapshot.error);

          return snapshot.hasData
              ? PhotosList(photos: snapshot.data)
              : Center(child: CircularProgressIndicator());
        },
      ),
    );
  }
}

class PhotosList extends StatelessWidget {
  final List<Photo> photos;

  PhotosList({Key key, this.photos}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return GridView.builder(
      gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
        crossAxisCount: 2,
      ),
      itemCount: photos.length,
      itemBuilder: (context, index) {
        return ListTile(
          leading: Icon(Icons.album),
          title: Column(  children: [
            Text(photos[index].symbol),
            //Text(photos[index].companyName),
          ],
          ),
          subtitle: Column(
            children: [
              // Text( ' ${photos[index].stats["stats"]["dividendYield"]["companyName"]}'),
              //  Text( ' ${photos[index].data["quote"]["iexRealtimePrice"]}' ' ${photos[index].stats["stats"]["dividendYield"]["companyName"]}'),
              // Text( ' ${photos[index].data["quote"]["iexRealtimePrice"]}'),
              Text ( '${photos[index].data["stats"]["dividendYield"] ?? ""}'),
              Text ( '${photos[index].data["stats"]["week52change"] ?? ""}'),
              Text ( '${photos[index].data["quote"]["companyName"] ?? ""}'),
            ],
          ),
          //title: Text(photos[index].symbol),
          //subtitle: Text( ' ${photos[index].stats["stats"]["dividendYield"]["companyName"]}'),
          //subtitle: Text( ' ${photos[index].data["quote"]["iexRealtimePrice"]}' ' ${photos[index].stats["stats"]["dividendYield"]["companyName"]}'),
          // subtitle: Text( ' ${photos[index].data["quote"]["iexRealtimePrice"]}'),
          // subtitle: Text ( ' ${photos[index].stats["stats"]["dividendYield"]}'),
        );
      },
    );
  }
}