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！