c# - 从类属性创建通用列表

Question

我正在尝试制作保存有关学生的数据的类(class)，以及他的带有标记的类(class)列表。但是当我尝试添加数据进行测试时，我在“student.courses.Add(course);”处出错，即“对象引用未设置为对象的实例。”谁能告诉我哪里做错了？

static void Main(string[] args)
{
    var student = new Student();
    student.id = 1;
    student.name = "John";
    student.lastName = "K.";

    var course = new Course();
    course.code = 123;
    course.nameOfCourse = "Course Name";
    student.courses.Add(course);
}

public class Student
{
    public int id { get; set; }
    public string name { get; set; }
    public string lastName { get; set; }
    public List<Course> courses { get; set; }
}


public class Course
{
    public int code { get; set; }
    public string nameOfCourse { get; set; }
    public int mark{ get; set; }
}

Answer 1

您没有初始化 courses 属性:

    var student = new Student();
    student.Courses = new List<Course>();
    student.Id = 1;
    student.Name = "John";
    student.LastName = "K.";

但最好在 Student 类中初始化它，这样会是:

public class Student
{
    private List<Course> courses = new List<Course>();

    public int Id { get; set; }
    public string Name { get; set; }
    public string LastName { get; set; }
    public List<Course> Courses 
    { 
       get
       {
          return courses;
       }
       set
       {
          courses = value;
       }
    }
}

旁注:最好用大写字母命名公共(public)属性，用小写字母命名私有(private)字段。