Error: Property 'body' cannot be accessed on 'Response?' because it is potentially null

Question

所以我正在尝试学习飞镖和扑动，到目前为止一切顺利。但是现在我陷入了一个我无法处理的错误。我编写了一个函数，该函数应该异步 return 来自 https://blockchain.info/ticker.

的实际 BTC 价格

唯一 return 是错误 :

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;
           ^

我的代码：

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']
    );
  }
}

最后要提的事情：我是运行 Android 模拟器上的应用程序，由 Android Studio 提供支持；请随时提供您的任何建议（在代码改进方面），即使它不能解决我的问题。

Answer 1

要消除该错误，您需要使用告诉编译器 snapshot.data 不会为 null。

if (statusCode == 200) {
  return Text(
 "${BTCPrice.fromJson(jsonDecode(snapshot.data!.body)).eur}"); // adding ! on data
}

编辑

您在评论中提到的无关错误：

unexpected character (at character 1) <html><head><title>loading...</title></head><body><script type='text/javasc... ^

将通过更改此

中的 GET 请求来解决

final response = await http.get(Uri.https('blockhain.info', 'ticker'));

至此

final response = await http.get(Uri.parse('https://blockchain.info/ticker'));

Error: Property 'body' cannot be accessed on 'Response?' because it is potentially null

Error: Property 'body' cannot be accessed on 'Response?' because it is potentially null

mobile

dart

android-studio

flutter

编辑