Xml序列化自引用/循环引用问题2

public class Student
{
    public int ID { get; set; }
    public string Name { get; set; }

    //[XmlIgnore]
    public Grade Grade { get; set; }
}
public class Grade
{
    public int GradeID { get; set; }
    public string GradeName { get; set; }
    public List<Student> Students { get; set; }
}

//创建班级
Grade gradeOne = new Grade() { GradeID = 1, GradeName = "班级1" };
gradeOne.Students = new List<Student>();
//添加班级下的学生
Student stu = new Student();
stu.ID = 1;
stu.Name = "张三";
//设置学生所属的班级 
/*
    * 1.如果指定学生的班级 就会抛出异常：序列化类型 Test.Grade 的对象时检测到循环引用。
    * 2.解决方法1：在创建的时候不指定子类对应的父类
    * 3.解决方法2：在子类的父类对象属性，添加[XmlIgnore]
    */
stu.Grade = gradeOne;
gradeOne.Students.Add(stu);
XmlSerializer xmls = new XmlSerializer(gradeOne.GetType());
string content;
using (MemoryStream ms = new MemoryStream())
{
    xmls.Serialize(ms, gradeOne);
    ms.Position = 0;
    using (StreamReader reader = new StreamReader(ms))
    {
        content = reader.ReadToEnd();
    }
}
Console.WriteLine(content);