Flutter : Unable to fetch json file data from an api - json

Question

Hello Everyone I am new to flutter during practicing While trying to fetch JSON data from an api I am unable to complete the operation and receiving the below mentioned error. I have attached my entire program and error notification for your suggestions.
What this program is about?
I am trying to fetch the cryptocurrency price details from an api and trying to display the few details of that website in my app. while doing that the data type which i mentioned in the code creating some error and i tried to change the data type and other things but still it is not solved.
main.dart
import 'package:flutter/material.dart';
import 'package:fluttercrypto/home_page.dart';
import 'package:http/http.dart' as http;
import 'dart:async';
import 'dart:convert';
void main() async {
List currencies = await getCurrency();
print(currencies);
runApp(MyApp(currencies));
}
class MyApp extends StatelessWidget {
final List _currencies;
MyApp(this._currencies); // This widget is the root of your application.
#override
Widget build(BuildContext context) {
return MaterialApp(
debugShowCheckedModeBanner: false,
theme: ThemeData(
primarySwatch: Colors.red,
),
home: HomePage(_currencies),
);
}
}
Future<List> getCurrency() async {
String cryptoUrl =
"https://api.coingecko.com/api/v3/coins/markets?vs_currency=usd&ids";
http.Response response = await http.get(Uri.parse(cryptoUrl));
return jsonDecode(response.body);
}
'''
**homepage.dart**
'''import 'package:flutter/material.dart';
class HomePage extends StatefulWidget {
final List currencies;
HomePage(this.currencies);
#override
_HomePageState createState() => _HomePageState();
}
class _HomePageState extends State<HomePage> {
List currencies;
final List<MaterialColor> _colors = [Colors.blue, Colors.indigo, Colors.red];
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text("Crypto Tracker"),
),
body: cryptoWidget(),
);
}
Widget cryptoWidget() {
return Container(
child: Column(
children: [
Flexible(
child: ListView.builder(
itemCount: widget.currencies.length,
itemBuilder: (BuildContext context, int index) {
final Map currency = widget.currencies[index];
final MaterialColor color = _colors[index % _colors.length];
return _getListItemUi(currency, color);
},
),
),
],
),
);
}
ListTile _getListItemUi(Map currency, MaterialColor color) {
return ListTile(
leading: CircleAvatar(
backgroundColor: color,
child: Text(currency['name'][0]),
),
title: Text(
currency['name'],
style: TextStyle(fontWeight: FontWeight.bold),
),
subtitle: _getSubtitleText(
currency['current_price'], currency['price_change_24h']),
isThreeLine: true,
);
}
Widget _getSubtitleText(int priceUSD, String percentageChange) {
TextSpan priceTextWidget = new TextSpan(
text: "\$$priceUSD\n", style: TextStyle(color: Colors.black));
String percentageChangeText = "24 hour : $percentageChange%";
TextSpan percentageChangeTextWidget;
if (double.parse(percentageChange) > 0) {
percentageChangeTextWidget = TextSpan(
text: percentageChangeText,
style: TextStyle(color: Colors.green),
);
} else {
percentageChangeTextWidget = TextSpan(
text: percentageChangeText,
style: TextStyle(color: Colors.red),
);
}
return RichText(
text: TextSpan(children: [priceTextWidget, percentageChangeTextWidget]),
);
}
}'''
**ERROR**
'''
======== Exception caught by widgets library =======================================================
The following _TypeError was thrown building:
type 'double' is not a subtype of type 'String'
When the exception was thrown, this was the stack:
#0 _HomePageState._getListItemUi (package:fluttercrypto/home_page.dart:54:46)
#1 _HomePageState.cryptoWidget.<anonymous closure> (package:fluttercrypto/home_page.dart:34:24)
#2 SliverChildBuilderDelegate.build (package:flutter/src/widgets/sliver.dart:455:22)
#3 SliverMultiBoxAdaptorElement._build (package:flutter/src/widgets/sliver.dart:1201:28)
#4 SliverMultiBoxAdaptorElement.createChild.<anonymous closure> (package:flutter/src/widgets/sliver.dart:1214:55)
...
====================================================================================================
======== Exception caught by widgets library =======================================================
The following _TypeError was thrown building:
type 'double' is not a subtype of type 'String'
When the exception was thrown, this was the stack:
#0 _HomePageState._getListItemUi (package:fluttercrypto/home_page.dart:54:46)
#1 _HomePageState.cryptoWidget.<anonymous closure> (package:fluttercrypto/home_page.dart:34:24)
#2 SliverChildBuilderDelegate.build (package:flutter/src/widgets/sliver.dart:455:22)
#3 SliverMultiBoxAdaptorElement._build (package:flutter/src/widgets/sliver.dart:1201:28)
#4 SliverMultiBoxAdaptorElement.performRebuild.processElement `enter code here`(package:flutter/src/widgets/sliver.dart:1145:67)
====================================================================================================
'''

Answer 1

It's probably because currency['price_change_24h'] isn't a string. When you pass it into _getSubtitleText do currency['price_change_24h'].toString().