如何从Flutter中的Firebase获取List

Question

我在实时数据库中有以下数据：

实时数据库

我想获得examQuestion

当我用这个的时候

  Future<void> restApiExam() async{
    var url= 'https://taw3ia-ac6b2.firebaseio.com/Exam.json';
    try{
      final response = await http.get(url);
      final extractedData = json.decode(response.body) as Map<String, dynamic>;
      final List<ExamModel> loadQuiz =[];
      extractedData.forEach((quizId , quizData){
        loadQuiz.add(ExamModel(
          examId : quizId,
          examTitle: quizData['examTitle'],
          examMark: quizData['examMark'],
          examPassingMark: quizData['examPassingMark'],
          examQuestion: (quizData['examQuestion'] as List<dynamic>).map((question) => QuestionModel(
            questionTitle: question['questionTitle'],
            questionAnswer: question['questionAnswer'].cast<String>(),
            questionImage: question['questionImage'],
            questionPoint: question['questionPoint'],
            rightAnswer: question['rightAnswer'],
          )
         ).toList() ,
          isPublic: quizData['isPublic'],
        ));
      });
      _exam = loadQuiz;
      notifyListeners();
    }
    catch(e){
      throw(e);
    }
  }

错误：

E/flutter（27654）：[ERROR： flutter/lib/ui/ui_dart_state.cc（166）]未处理的异常：类型_InternalLinkedHashMap

我的范例：

class ExamModel with ChangeNotifier {
  final String examId;
  final String examTitle;
  final String examMark;
  final String examPassingMark;
  final List<QuestionModel> examQuestion;
  final bool isPublic;


  ExamModel({
    @required this.examId,
    @required this.examTitle,
    @required this.examMark,
    @required this.examPassingMark,
    @required this.examQuestion,
    this.isPublic = false,
  });

}

我的问卷模型：

class QuestionModel with ChangeNotifier{

  final String restById;
  final String questionId;
  final String questionTitle;
  final String questionImage;
  final int questionPoint;
  final List<String> questionAnswer;
  final String rightAnswer;

  QuestionModel({
    @required this.restById,
    @required this.questionId,
    @required this.questionTitle,
    @required this.questionImage,
    @required this.questionPoint,
    @required this.questionAnswer,
    @required this.rightAnswer,
  });

}

Answer 1

在您的图像中：

您的字段称为“eaxmQuestion”，而不是“examQuestion”。有一个打字错误。我不确定这会解决您的问题，但这肯定是一个问题，因为在您的代码中，您正在调用quizData['examQuestion']。