问未处理的异常: NoSuchMethodError:在null (json分析)上调用了方法'[]‘

EN

{
    "Delhi": {
      "districtData": {
        "East Delhi": {
          "confirmed": 1,
          "lastupdatedtime": ""
        },
        "South West Delhi": {
          "confirmed": 3,
          "lastupdatedtime": ""
        },
        "West Delhi": {
          "confirmed": 2,
          "lastupdatedtime": ""
        },
        "North Delhi": {
          "confirmed": 3,
          "lastupdatedtime": ""
        },
        "New Delhi": {
          "confirmed": 3,
          "lastupdatedtime": ""
        },
        "South Delhi": {
          "confirmed": 2,
          "lastupdatedtime": ""
        },
        "North East Delhi": {
          "confirmed": 1,
          "lastupdatedtime": ""
        },
        "North West Delhi": {
          "confirmed": 3,
          "lastupdatedtime": ""
        },
        "Unknown": {
          "confirmed": 53,
          "lastupdatedtime": ""
        },
        "Delhi": {
          "confirmed": 1,
          "lastupdatedtime": ""
        }
      }
    }
  }

// To parse this JSON data, do
//
//     final indiaState = indiaStateFromJson(jsonString);

import 'dart:convert';

IndiaState indiaStateFromJson(String str) => IndiaState.fromJson(json.decode(str));

String indiaStateToJson(IndiaState data) => json.encode(data.toJson());

class IndiaState {
    Delhi delhi;

    IndiaState({
        this.delhi,
    });

    factory IndiaState.fromJson(Map<String, dynamic> json) => IndiaState(
        delhi: Delhi.fromJson(json["Delhi"]),
    );

    Map<String, dynamic> toJson() => {
        "Delhi": delhi.toJson(),
    };
}

class Delhi {
    Map<String, DistrictDatum> districtData;

    Delhi({
        this.districtData,
    });

    factory Delhi.fromJson(Map<String, dynamic> json) => Delhi(
        districtData: Map.from(json["districtData"]).map((k, v) => MapEntry<String, DistrictDatum>(k, DistrictDatum.fromJson(v))),
    );

    Map<String, dynamic> toJson() => {
        "districtData": Map.from(districtData).map((k, v) => MapEntry<String, dynamic>(k, v.toJson())),
    };
}

class DistrictDatum {
    int confirmed;
    String lastupdatedtime;

    DistrictDatum({
        this.confirmed,
        this.lastupdatedtime,
    });

    factory DistrictDatum.fromJson(Map<String, dynamic> json) => DistrictDatum(
        confirmed: json["confirmed"],
        lastupdatedtime: json["lastupdatedtime"],
    );

    Map<String, dynamic> toJson() => {
        "confirmed": confirmed,
        "lastupdatedtime": lastupdatedtime,
    };
}

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:sample_project_for_api/model.dart';

class HomePage extends StatefulWidget {
  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  bool isLoading = false;
  List<Cities> citilesList = List();

  // here i have taken the  json locally which you posted on stack 
  Future<String> loadFromAssets() async {
    return await rootBundle.loadString('json/parse.json');
  }

  @override
  void initState() {
    super.initState();
    givenFunction();
  }

  Future givenFunction() async {
    setState(() {
      isLoading = true;
    });

    //final httpRequest = await http.get(districtAPI);
    //final json = jsonDecode(httpRequest.body);
    // you can make the http call above just uncomment is and comment the below line
    String jsonString = await loadFromAssets();
    // Here you can just replace down your httpRequest.body with jsonString
    final indiaState = indiaStateFromJson(jsonString);
    indiaState.delhi.districtData.forEach((key, value) {
      // This column is show you the values are getting fetched and printed below
      print('This is the key : ' + key);
      print('Confirmed :' + value.confirmed.toString());
      citilesList.add(Cities(key, value.confirmed));
    });
    setState(() {
      isLoading = false;
    });
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: isLoading
            ? CircularProgressIndicator()
            : ListView.builder(
                itemCount: citilesList.length,
                itemBuilder: (BuildContext context, int index) {
                  return Container(
                    child: Card(
                      margin:
                          EdgeInsets.symmetric(vertical: 10, horizontal: 10),
                      child: Padding(
                        padding: const EdgeInsets.all(15.0),
                        child: Row(
                          children: <Widget>[
                            Text(citilesList[index].state + ": "),
                            Text(citilesList[index].confirmed.toString())
                          ],
                        ),
                      ),
                    ),
                  );
                },
              ),
      ),
    );
  }
}

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

class Cities {
  final String state;
  final int confirmed;

  Cities(this.state, this.confirmed);
}