The argument type 'String?' can't be assigned to the parameter type 'String'

Question

具体报错内容:
lib/Object_type_oop.dart:201:37: Error: The argument type ‘String?’ can’t be assigned to the parameter type ‘String’ because ‘String?’ is nullable and ‘String’ isn’t.

return Student(stu._school, stu.name, stu.age);

希望老师能够解答, 谢谢 。

Answer 1

CrazyCodeBoy 2022-02-18 10:37:43

String get 改成了String? get

Answer 2

CrazyCodeBoy 2022-02-17 09:18:00

完整代码贴一下我帮你看看

• 提问者 慕无忌6890528 #1

  class Student extends Person {
  
    String? _school; // 通过下划线来标识当前类的私有变量 。
    // final String city;
    String? city;
    String? country;
    String? name;
  
  
    Student(this._school, String name, int age, {this.city, this.country = '设置为默认参数'})
    :
      name = '$country.$city',
      super(name, age){
        print('构造方法体不是必须的');
      }
  
  
    Student.cover(Student stu)
    :
      super(stu.name, stu.age) {
        print('命名构造方法: 也是 有自己的方法提的');
      }
  
  
    factory Student.stu(Student stu) {
      return Student(stu._school, stu.name, stu.age);
    }
  
  
    // 可以为私有字段设置 getter 来让外界获取到私有字段
    String get school => _school;
  
    // 可以为私有字段设置 setter 来控制外界对私有字段的修改
    set school(String value) {
      _school = value;
      print('在这里设置私有变量');
    }
  
  
    /**
     * 11. 静态方法:
     *     1. 我们需要在方法名前面使用关键字 static 来标识
     */
    static doPrint (String str) {
      print('doPrint:$str');
    }
  
  
  }