class 선언 오류

screen_quiz.dart / class QuizScreen 
screen_result.dart / class ResultScreen
screen_cadidate.dart / class CandWidget 

각파일에 있는 클래스들에서 오류가납니다..ㅠㅠ

This class (or a class that this class inherits from) is marked as '@immutable', but one or more of its instance fields aren't final: CandWidget.tap, CandWidget.text, CandWidget.index, CandWidget.width, CandWidget.answerStatedartmust_be_immutabl