Flutter / Dart - parse json time series as map with key and value - json

Question

I encountered the below message on "anonymous closure" in the TimeSeriesAdjusted.fromJson which I think may be the issue but I could not figure where may have gone wrong.
[VERBOSE-2:ui_dart_state.cc(199)] Unhandled Exception: type 'Null' is not a subtype of type 'String'
#0 new PriceData.fromJson (package:flutter_app_watchlist/model/TimeSeriesAdjusted.dart:60:28)
#1 new TimeSeriesAdjusted.fromJson. *****anonymous closure>** (package:flutter_app_watchlist/model/TimeSeriesAdjusted.dart:87:116)
#2 MapMixin.map (dart:collection/maps.dart:170:28)
#3 new TimeSeriesAdjusted.fromJson (package:flutter_app_watchlist/model/TimeSeriesAdjusted.dart:87:62)
#4 getData (package:flutter_app_watchlist/main.dart:21:52)
*****asynchronous suspension>**
Below is the time series json (saved as data.json in folder assets) which I would like to parse.
{
"Meta Data": {
"1. Information": "Daily Time Series with Splits and Dividend Events",
"2. Symbol": "IBM",
"3. Last Refreshed": "2021-06-07",
"4. Output Size": "Compact",
"5. Time Zone": "US/Eastern"
},
"Time Series (Daily)": {
"2021-06-07": {
"1. open": "147.55",
"2. high": "148.74",
"3. low": "147.17",
"4. close": "148.02",
"5. adjusted close": "148.02",
"6. volume": "3462712",
"7. dividend amount": "0.0000",
"8. split coefficient": "1.0"
},
"2021-06-04": {
"1. open": "146.0",
"2. high": "147.55",
"3. low": "145.76",
"4. close": "147.42",
"5. adjusted close": "147.42",
"6. volume": "3117905",
"7. dividend amount": "0.0000",
"8. split coefficient": "1.0"
},
"2021-06-03": {
"1. open": "144.91",
"2. high": "145.88",
"3. low": "144.04",
"4. close": "145.55",
"5. adjusted close": "145.55",
"6. volume": "4130741",
"7. dividend amount": "0.0000",
"8. split coefficient": "1.0"
},
"2021-06-02": {
"1. open": "144.62",
"2. high": "145.75",
"3. low": "144.11",
"4. close": "145.72",
"5. adjusted close": "145.72",
"6. volume": "2786916",
"7. dividend amount": "0.0000",
"8. split coefficient": "1.0"
},
"2021-06-01": {
"1. open": "145.0",
"2. high": "145.83",
"3. low": "143.75",
"4. close": "144.19",
"5. adjusted close": "144.19",
"6. volume": "2417455",
"7. dividend amount": "0.0000",
"8. split coefficient": "1.0"
}
}
}
Below are the codes:
import 'package:flutter/material.dart';
import 'dart:convert';
import 'package:flutter/services.dart' show rootBundle;
getData() async {
String data = await rootBundle.loadString('assets/data.json');
TimeSeriesAdjusted jsonData = TimeSeriesAdjusted.fromJson(json.decode(data));
print(jsonData.toString());
}
void main() async {
WidgetsFlutterBinding.ensureInitialized();
getData();
} // main
class TimeSeriesMetaData {
final String information; // "1. Information": "Daily Time Series with Splits and Dividend Events"
final String symbol; // "2. Symbol": "IBM"
final String lastRefreshed; // "3. Last Refreshed": "2021-06-07"
final String outputSize; // "4. Output Size": "Compact"
final String timezone; // "5. Time Zone": "US/Eastern"
TimeSeriesMetaData({
required this.information,
required this.symbol,
required this.lastRefreshed,
required this.outputSize,
required this.timezone});
factory TimeSeriesMetaData.fromJson(dynamic json) {
return TimeSeriesMetaData(
information: json["1. Information"],
symbol: json["2. Symbol"],
lastRefreshed: json["3. Last Refreshed"],
outputSize: json["4. Output Size"],
timezone: json["5. Time Zone"]);
} // factory TimeSeriesMetaData.fromJson
#override
String toString() {
return 'TimeSeriesMetaData: {1. Information = $information, '
'2. Symbol = $symbol, '
'3. Last Refreshed = $lastRefreshed, '
'4. Output Size = $outputSize, '
'5. Time Zone = $timezone, }';
} // toString
} // class TimeSeriesMetaData
class PriceData {
final String open; // "1. open": "147.55"
final String high; // "2. high": "148.74"
final String low; // "3. low": "147.17"
final String close; // "4. close": "148.02"
final String adjustedClose; // "5. adjusted close": "148.02"
final String volume; // "6. volume": "3462712"
final String dividendAmount; // "7. dividend amount": "0.0000"
final String splitCoefficient; // "8. split coefficient": "1.0"
PriceData({
required this.open,
required this.high,
required this.low,
required this.close,
required this.adjustedClose,
required this.volume,
required this.dividendAmount,
required this.splitCoefficient});
factory PriceData.fromJson(dynamic json) {
return PriceData(
open: json["1. open"],
high: json["2. high"],
low: json["3. low"],
close: json["4. close"],
adjustedClose: json["5. adjustedClose"],
volume: json["6. volume"],
dividendAmount: json["7. dividendAmount"],
splitCoefficient: json["8. splitCoefficient"]);
} // factory TimeSeriesMetaData.fromJson
#override
String toString() {
return 'PriceData: {1. open = $open, 2. high = $high, '
'3. low = $low, 4. close = $close, 5. adjustedClose = $adjustedClose, '
'6. volume = $volume, 7. dividendAmount = $dividendAmount, '
'8. splitCoefficient = $splitCoefficient}';
} // toString
} // class TimeSeriesMetaData
class TimeSeriesAdjusted {
final TimeSeriesMetaData timeSeriesMetaData;
final Map<String, PriceData> timeSeriesDaily;
TimeSeriesAdjusted({
required this.timeSeriesMetaData, // security symbol e.g. IBM
required this.timeSeriesDaily, // security type e.g. common stock
});
factory TimeSeriesAdjusted.fromJson(Map<String, dynamic> json) {
return TimeSeriesAdjusted(
timeSeriesMetaData: TimeSeriesMetaData.fromJson(json["Meta Data"]),
timeSeriesDaily: Map.from(json["Time Series (Daily)"]).map((k,v) => MapEntry<String, PriceData>(k, PriceData.fromJson(v))),
);
} // fromJson - extract from Json
#override
String toString() {
//return 'TimeSeriesAdjusted: $timeSeriesMetaData';
return 'TimeSeriesAdjusted: $timeSeriesMetaData, $timeSeriesDaily';
} // toString
} // class TimeSeriesAdjusted

Answer 1

ah... i realised where the mistake lies.. i got the attribute name incorrect in PriceData.fromJson when i called json['xxx]. below corrected for 5, 7, 8
factory PriceData.fromJson(dynamic json) {
return PriceData(
open: json["1. open"],
high: json["2. high"],
low: json["3. low"],
close: json["4. close"],
adjustedClose: json["5. adjusted close"],
volume: json["6. volume"],
dividendAmount: json["7. dividend amount"],
splitCoefficient: json["8. split coefficient"]);
} // factory TimeSeriesMetaData.fromJson