我在飞镖中得到不可为空的实例，我该如何解决？

Question

这是我的代码

 void main() {
    user userOne=user('silver',19);
    print(userOne.name);
    superUser userTwo=superUser('sasha',1);
    print(userTwo.name);
 }

 class user{
  int age;
  String name;
  user(String name,int age){
    this.name=name;
    this.age=age;
  }
  void login(){
    print("user has logged in");
  }
}
class superUser extends user{
  superUser(String name,int age):super(name,age);
  
  void publish(){
    print("publish update");
  }
}

虽然我在构造函数中初始化了变量，但还是遇到了这些错误。

Non-nullable instance field 'name' must be initialized.
Non-nullable instance field 'age' must be initialized.

我应该将整数变量初始化为0，将字符串变量初始化为空字符串吗？

Answer 1

你可以这样做：

 void main() {
    user userOne=user('silver',19);
    print(userOne.name);
    superUser userTwo=superUser('sasha',1);
    print(userTwo.name);
 }

 class user{
  int age;
  String name;
  // Syntactic sugar for setting name and age
  // before the constructor body runs.
  user(this.name, this.age);
   
  void login(){
    print("user has logged in");
  }
}
class superUser extends user{
  superUser(String name,int age):super(name,age);
  
  void publish(){
    print("publish update");
  }
}

此外，类名最好使用 UpperCamelCase，意思是 User、SuperUser 而不是 user、superuser。

Answer 2

在初始化之前，您不能使用不可为空的属性。所以，你有两个选择：

1- 声明后期变量。

class user{
  late int age;
  late String name;
  user(String name,int age){
    this.name=name;
    this.age=age;
  }
  void login(){
    print("user has logged in");
  }
}

2- 可以为空。

class user{
      int? age;
      String? name;
      user(String name,int age){
        this.name=name;
        this.age=age;
      }
      void login(){
        print("user has logged in");
      }
    }