实现比较器接口IComparable<T>，让自定义类型数组也能排序

using System;

namespace LinqDemo1
{
    class Program
    {
        static void Main(string[] args)
        {
            Person[] persons =
            {
                new Person {FirstName = "Damon", LastName = "Hill"},
                new Person {FirstName = "Niki", LastName = "Lauda"},
                new Person {FirstName = "Ayrton", LastName = "Senna"}
            };
            Array.Sort(persons);//现在可以比较了
            foreach (var p in persons)
            {
                Console.WriteLine(p);
            }

            Console.ReadKey();
        }
    }

    class Person : IComparable<Person>
    {
        public int CompareTo(Person other)
        {
            if (other == null)
            {
                return 1;
            }
            int result = string.Compare(this.LastName, other.LastName);
            if (result == 0)
            {
                result = string.Compare(this.FirstName, other.FirstName);
            }
            return result;
        }

        public override string ToString()
        {
            return string.Format("{0} {1}", FirstName, LastName);
        }

        public string FirstName { get; set; }
        public string LastName { get; set; }
    }
}

但有时候Person类是别人的类，无法修改，那怎么办呢？

在这种情况下，就可以定义一个新类，如：PersonComparer继承IComparer<Person>

using System;
using System.Collections;
using System.Collections.Generic;

namespace LinqDemo1
{
    class Program
    {
        static void Main(string[] args)
        {
            Person[] persons =
            {
                new Person {FirstName = "Damon", LastName = "Hill"},
                new Person {FirstName = "Niki", LastName = "Lauda"},
                new Person {FirstName = "Ayrton", LastName = "Senna"}
            };
            Array.Sort(persons, new PersonComparer(PersonCompareType.FirstName));

            foreach (var p in persons)
            {
                Console.WriteLine(p);
            }

            Console.ReadKey();
        }
    }

    public enum PersonCompareType
    {
        FirstName,
        LastName
    }

    public class PersonComparer : IComparer<Person>
    {
        private PersonCompareType compareType;

        public PersonComparer(PersonCompareType compareType)
        {
            this.compareType = compareType;
        }

        public int Compare(Person x, Person y)
        {
            if (x == null && y == null) return 0;
            if (x == null) return 1;
            if (y == null) return -1;

            switch (compareType)
            {
                case PersonCompareType.FirstName:
                    return string.Compare(x.FirstName, y.FirstName);
                case PersonCompareType.LastName:
                    return string.Compare(x.LastName, y.LastName);
                default:
                    throw new ArgumentException("unexpected compare type");
            }

        }
    }

    public class Person
    {
        public override string ToString()
        {
            return string.Format("{0} {1}", FirstName, LastName);
        }

        public string FirstName { get; set; }
        public string LastName { get; set; }
    }
}

Array 类还提供了Sort()多个重载方法，它需要将一个委托作为参数，这个参数可以传递给方法，从而比较2个对象，而不需要依赖IComparable或IComparer接口，也就是说上面都白折腾了，有更高级的做法！那就是委托！