Question

我在dart：convert库中遇到错误。

请帮助我解决问题。这是我的阻止代码：

import 'dart:async' show Future, Stream;
import 'dart:convert' show json, UTF8;
import 'dart:io' show HttpClient;

import 'package:http/http.dart' as http;

import 'package:flutter/services.dart' show rootBundle;

/// PODO for questions
class Question {
  String question;
  bool answer;

  Question.fromJson(Map jsonMap) :
    question = jsonMap['question'],
    answer = jsonMap['answer'];

  String toString() {
    return '$question is $answer';
  }
}

Future<List<Question>> loadQuestionsLocally() async {
  final jsonString = await rootBundle.loadString('assets/questions.json');
  final questions = json.decode(jsonString);
  return questions.map(
    (q) => new Question.fromJson(q)
  ).toList();
}

Future<List<Question>> loadQuestionsNetwork() async {
  final req = await new HttpClient().getUrl(
    Uri.parse('https://raw.githubusercontent.com/mjohnsullivan/flutter_quiz/master/assets/questions.json')
  );
  final res = await req.close();
  final body = await res.transform(UTF8.decoder).join();
  final questions = json.decode(body);
  return questions.map(
    (q) => new Question.fromJson(q)
  ).toList();
}
........

在代码行中，IDE显示错误消息'Undfine name UTF8'

最终主体=等待res.transform（UTF8.decoder）.join（）;

我使用的是flutter版本，如下所示：

$ flutter --version
Flutter 1.2.1 • channel stable • https://github.com/flutter/flutter.git
Framework • revision 8661d8aecd (3 weeks ago) • 2019-02-14 19:19:53 -0800
Engine • revision 3757390fa4
Tools • Dart 2.1.2 (build 2.1.2-dev.0.0 0a7dcf17eb)

该如何解决？谢谢!!!

Answer 1

在Dart 2中，名称已更改为lowerCamelCase。似乎是从旧示例复制过来的。

使用utf8代替UTF8。

库dart：convert不会导出显示名称为'UTF8'的成员

1 个答案: