so I'am trying to learn dart and flutter and everything went well so far. But now I'am stuck at an error which I cannot handle. I coded a function which is supposed to asynchronously return the actual BTC price from https://blockchain.info/ticker.
Only thing it returns is errors:
Error: Property 'body' cannot be accessed on 'Response?' because it is potentially null.
- 'Response' is from 'package:http/src/response.dart' ('/D:/flutter/.pub-cache/hosted/pub.dartlang.org/http-0.13.4/lib/src/response.dart').
Try accessing using ?. instead.
return Text("${BTCPrice.fromJson(jsonDecode(snapshot.data.body)).eur}");
^^^^
/D:/flutter/packages/flutter/lib/src/widgets/async.dart:242:12: Context: 'data' refers to a property so it couldn't be promoted.
See http://dart.dev/go/non-promo-property
final T? data;
^
My Code:
import 'dart:convert';
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
Future<http.Response> fetchBTCPrice() async {
final response = await http.get(Uri.https('blockhain.info', 'ticker'));
return response;
}
Widget buildBTCPrice() {
return FutureBuilder<http.Response>(
future: fetchBTCPrice(),
builder: (context, snapshot) {
if (snapshot.hasData) {
int? statusCode = snapshot.data?.statusCode;
if (statusCode == 200) {
return Text("${BTCPrice.fromJson(jsonDecode(snapshot.data.body)).eur}");
}
return Text('$statusCode');
} else if (snapshot.hasError) {
return Text('${snapshot.error}');
}
return CircularProgressIndicator();
},
);
}
class BTCPrice {
final double eur;
BTCPrice({required this.eur});
factory BTCPrice.fromJson(Map<String, dynamic> json) {
print(json);
return BTCPrice(
eur: json['eur']['15m']
);
}
}
Last things to mention: I'am running the application on a Android Emulator powerd by Android Studio; and please feel free to hand over any advice you have (in terms of code improvement), even if it is not fixing my issue.
CodePudding user response：
To get rid of that error you need to use the bang operator to tell the compiler that snapshot.data won't be null.
if (statusCode == 200) {
return Text(
"${BTCPrice.fromJson(jsonDecode(snapshot.data!.body)).eur}"); // adding ! on data
}
Edit
The unrelated error you mentioned in your comment:
unexpected character (at character 1) <html><head><title>loading...</title></head><body><script type='text/javasc... ^
would be fixed by changing your GET request from this
final response = await http.get(Uri.https('blockhain.info', 'ticker'));
to this
final response = await http.get(Uri.parse('https://blockchain.info/ticker'));