Stack Overflow answer to Question https://stackoverflow.com/questions/60286533/why-i-cant-refer-to-a-key-in-an-objects-another-key

main.dart

var object = {
  "allStudents": [
    {
      "name": "John",
      "hobbies": {
        "sport": "Football",
        "music": "Piano"
      } ,
    },
    {
      "name": "Julyo",
      "hobbies": {
        "sport": "Vollyball",
        "music": "Guitar"
      } ,
    },
  ],
};

class Student {
  String name;
  dynamic hobbies;
  Student({this.name, this.hobbies});
}

class Hobbies {
  String sport;
  String music;
  Hobbies({this.sport, this.music});
}

List<Student> studentsList = [];

List getStudentsList () {
  //new Line here - ignore the unnecessary cast warning
  studentsList = (object["allStudents"] as List<Map<String,dynamic>>).map((stu)=>
  Student(
    name: stu["name"] ,
    hobbies: Hobbies(
      sport: stu['hobbies']["sport"] ,
        music:stu['hobbies']["music"],
    ) ,
  )
  ).toList();
  return studentsList;
}


void main(){
  print(getStudentsList()[0].hobbies.sport);
}