Flutter(dart) 错误：无法将参数类型分配给参数类型 'dynamic Function(List<student> ？）'</student>

Question

在Flutter的新版本中遇到错误如下。

错误：参数类型“列表？” 无法分配给参数类型“动态函数（列表？）”。 （argument_type_not_assignable 在 [temel_widget] lib\screens\student_add.dart:14）

class StudentAdd extends StatefulWidget {
    //Student addStudent = Student.withId(0, "", "", 0);
    List<Student>? students;
    StudentAdd(List<Student>? students) {
    this.students = students;
  }
  @override
  State<StatefulWidget> createState() {
    return _StudentAddState(students);  **This here error message**
  }
}

class _StudentAddState extends State with StudentValidationMixin {
  //Student addStudent = Student.withId(0, "", "", 0);

  List<Student>? students=[];
  var student = Student.withoutInfo();
  var formKey = GlobalKey<FormState>();

  _StudentAddState(StudentAdd(List<Student>? students)) {
    this.students = students;
  }

Answer 1

如果你检查这个tudentAdd(List<Student>? students)你正在调用_StudentAddState中的StudentAdd构造函数。

_StudentAddState(StudentAdd(List<Student>? students)) {
    this.students = students;
  }

你需要像

_StudentAddState(List<Student>? students) {
    this.students = students;
  }

您也可以避免传递参数，而我们可以使用widget.varableName访问 class 级变量。 并启动项目我们在initState中有 initState

class StudentAdd extends StatefulWidget {
  StudentAdd({
    Key? key,
    required this.students,
  }) : super(key: key);

  List<Student>? students;
  @override
  State<StudentAdd> createState() => _StudentAddState();
}

class _StudentAddState extends State<StudentAdd> {
  @override
  void initState() {
    super.initState();

    ///getting students also, this can be done anyplace on state class
    print(widget.students?.length);
  }
 //....
}

Answer 2

检查 state 构造函数中的参数应该是

_StudentAddState(List<Student>? students)

而且您不需要将数据从 Widget 传递到其 state，您可以使用widegt.data从 State class 访问 widget 数据

class _StudentAddState extends State<StudentAdd> with StudentValidationMixin {

  List<Student>? get students = widget.students;
  var student = Student.withoutInfo();
  var formKey = GlobalKey<FormState>();

  ...
}