public CreateQuizViewModel()
        {
            Quiz = new Quiz();
            Questions = new ObservableCollection<Question>();
            _questionRepository = new QuestionRepository();

        }
 private void BtnSaveQuiz_OnClick(object sender, RoutedEventArgs e)
 {
     
     var viewModel = this.DataContext as CreateQuizViewModel;
     if (viewModel == null) return;
     {
         Quiz quiz = new Quiz
         {
             Time = _totalTimeOfQuiz,
             SafeLimit = _safeLimit
         };
         viewModel.SaveQuizCommand.Execute(quiz);
     }
 }