比较规则

CompareTo(Object)

将此实例与指定对象进行比较并返回一个对二者的相对值的指示。

public int CompareTo (object? value);

参数value Object要比较的对象，或为 null。

返回Int32一个带符号数字，指示此实例和 value 的相对值。

类内实现比较器

//Person类，自带比较器
    public class Person : IEquatable<Person>, IComparable<Person>
    {
        public int age;
        public string name;
        public Person(int age)
        {
            this.age = age;
        }
        public Person(string name, int age) : this(age)
        {
            this.name = name;
        }
        public override string ToString()
        {
            return $"姓名：{this.name} + 年龄: {this.age}";
        }
        //实现可比较接口
        public int CompareTo(Person other)
        {
            if (other == null) return 1;
            return this.age.CompareTo(other.age);
        }
        //实现可相等接口
        public bool Equals(Person other)
        {
            if (other == null) return false;
            return this.age.Equals(other.age);
        }
        //运算符重载
        public static bool operator >(Person person, Person other)
        { if (other == null) return true; return person.age > other.age; }
        public static bool operator >=(Person person, Person other)
        { if (other == null) return true; return person.age >= other.age; }
        public static bool operator <(Person person, Person other)
        { if (other == null) return false; return person.age < other.age; }
        public static bool operator <=(Person person, Person other)
        { if (other == null) return false; return person.age <= other.age; }


    }

测试

static void test1()
        {
            List<Person> list = new List<Person>();
            Random r = new Random();
            for (int i = 0; i < 10; i++)
            { list.Add(new Person($"Tom{i}", r.Next(1, 100))); }
            foreach (var item in list)
            { Console.WriteLine(item.ToString()); }
            //Person自带比较器
            list.Sort();
            Console.WriteLine("排序后");
            foreach (var item in list)
            { Console.WriteLine(item.ToString()); }

        }

 运行结果

 类外实现

//学生类，无比较器，需要在外部专门声明一个比较器
    public class Student
    {
        public int age;
        public string name;
        public Student(int age)
        {
            this.age = age;
        }
        public Student(string name, int age) : this(age)
        {
            this.name = name;
        }
        public override string ToString()
        {
            return $"姓名：{this.name} + 年龄: {this.age}";
        }
    }
    //学生比较器，实现可比较接口（默认）
    public class StudentComparerAscend : IComparer<Student>
    {
        public int Compare(Student x, Student y)
        {
            int result;
            if(x==null&&y==null ) result= 0;
            if (x == null && y != null) result = -1;
            if (x != null && y == null) result = 1;
            result= x.age.CompareTo(y.age);
            return result;
        }
    }
    //学生比较器，实现可比较接口（反序）
    public class StudentComparerDescend : IComparer<Student>
    {
        public int Compare(Student x, Student y)
        {
            int result;
            if (x == null && y == null) result = 0;
            if (x == null && y != null) result = -1;
            if (x != null && y == null) result = 1;
            result = x.age.CompareTo(y.age);
            return -result;//实现反序
        }
    }

测试

       static void test2()
        {
            List<Student> list = new List<Student>();
            Random r = new Random();
            for (int i = 0; i < 10; i++)
            { list.Add(new Student($"Jack{i}", r.Next(1, 100))); }
            foreach (var item in list)
            { Console.WriteLine(item.ToString()); }
            //实例化升序比较器
            StudentComparerAscend comparerAscend = new StudentComparerAscend();
            //升序排序（默认）
            list.Sort(comparerAscend);
            Console.WriteLine("\n升序排序后");
            foreach (var item in list)
            { Console.WriteLine(item.ToString()); }
            //实例化降序比较器
            StudentComparerDescend comparerDescend = new StudentComparerDescend();
            //降序排序
            list.Sort(comparerDescend);
            Console.WriteLine("\n降序排序后");
            foreach (var item in list)
            { Console.WriteLine(item.ToString()); }
        }

运行结果