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

Question

In the new version of Flutter, I encountered an error as follows.

error: The argument type 'List?' can't be assigned to the parameter type 'dynamic Function(List?)'. (argument_type_not_assignable at [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

If you check this tudentAdd(List<Student>? students) you are calling StudentAdd constructor inside _StudentAddState .

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

you need to use like

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

Also you can avoid passing parameters while we can access class level variables using widget.varableName . And to initiate item We have initState inside state

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

Check the parameters in your state constructor it should be

_StudentAddState(List<Student>? students)

And you don't need to pass data from the Widget to its state, you can access widget data from the State class using widegt.data

class _StudentAddState extends State<StudentAdd> with StudentValidationMixin {

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

  ...
}