IComparable、IComparer接口

C#中，自定义类型，支持比较和排序，需要实现IComparable接口。IComparable接口存在一个名为CompareTo()的方法，接收类型为object的参数表示被比较对象，返回整型值：1表示当前对象大于被比较对象，0表示两者相等，-1表示当前对象小于被比较对象。

IComparable接口：

public int CompareTo(object o) {}

IComparer接口：（比较器）

若想以更加灵活的方式对自定义类进行比较，可以声明一个继承自IComparer接口的比较器，实现接口方法Comprae()，接收2个object类型参数作为比较对象，返回整型值：1表示前者大于后者，0表示两者相等，-1表示前者小于后者。

public int Compare(object x, object y) {}

IComparable是“可比较的”意思，自定义类实现该接口，就具有可比较的功能；IComparer是“比较器”的意思，实现该接口的类就是一个比较器，可以将比较器“注入”类中，使类具有比较和排序的功能。

IComparable接口示例代码

定义学生类，该类实现IComparable接口的CompareTo方法，该方法对Age 进行大小比较。

    public class Student : IComparable
    {
        public string Name { get; set; }
        public string Sex { get; set; }
        public int Age { get; set; }
        public int CompareTo(object obj)
        {
            Student stu = obj as Student;
            if (Age > stu.Age)
            {
                return 1;
            }
            else if (Age == stu.Age)
            {
                return 0;
            }
            else
            {
                return -1;
            }
        }
    }

调用List<T>.Sort方法实现stuList按照学生的年龄来排序。

        static void Main(string[] args)
        {
            List<Student> stuList = new List<Student>();
            stuList.Add(new Student() { Name = "tiana0", Sex = "Man", Age = 18 });
            stuList.Add(new Student() { Name = "tiana1", Sex = "Woman", Age = 20 });
            stuList.Add(new Student() { Name = "tiana2", Sex = "Woman", Age = 16 });
            stuList.Add(new Student() { Name = "tiana3", Sex = "Man", Age = 21 });
            stuList.Add(new Student() { Name = "tiana4", Sex = "Woman", Age = 19 });
            stuList.Sort();
            foreach (Student stu in stuList)
            {
                Console.WriteLine("Name=" + stu.Name + ";Sex=" + stu.Sex + ";Age=" + stu.Age);
            }
        }

IComparer接口示例代码

定义学生类。

 public class Student
    {
        public string Name { get; set; }
        public string Sex { get; set; }
        public int Age { get; set; }
    }

自定义比较器AgeComparer，实现接口IComparer<Student>，对学生年龄进行比较。

    public class AgeComparer : IComparer<Student>
    {
        public int Compare(Student x, Student y)
        {
            return x.Age.CompareTo(y.Age);
        }
    }

自定义比较器NameComparer，实现接口IComparer<Student>，对学生姓名进行比较。

public class NameComparer : IComparer<Student>
    {
        public int Compare(Student x, Student y)
        {
            return x.Name.CompareTo(y.Name);
        }
    }

调用List<T>.Sort方法实现stuList按照学生的年龄与姓名排序。

        static void Main(string[] args)
        {
            List<Student> stuList = new List<Student>();
            stuList.Add(new Student() { Name = "aki", Sex = "Man", Age = 18 });
            stuList.Add(new Student() { Name = "cki", Sex = "Woman", Age = 20 });
            stuList.Add(new Student() { Name = "dki", Sex = "Woman", Age = 16 });
            stuList.Add(new Student() { Name = "bki", Sex = "Man", Age = 21 });
            stuList.Add(new Student() { Name = "fki", Sex = "Woman", Age = 19 });
            stuList.Sort(new AgeComparer());
            Console.WriteLine("按照年龄排序：");
            foreach (Student stu in stuList)
            {
                Console.WriteLine("Name=" + stu.Name + ";Sex=" + stu.Sex + ";Age=" + stu.Age);
            }
            stuList.Sort(new NameComparer());
            Console.WriteLine();
            Console.WriteLine("按照名称排序：");
            foreach (Student stu in stuList)
            {
                Console.WriteLine("Name=" + stu.Name + ";Sex=" + stu.Sex + ";Age=" + stu.Age);
            }
        }