扩展接口

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace WebApp2010
{
public class UserProfilerService : IUserProfiler
{
public string GetUserProfiler(string UserId)
{
if (UserId == "fasdfasdfasdfas")
return "到北京";
else return string.Empty;
}
}
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace WebApp2010
{
public static class Extensions
{
public static string MyProfiler(this IUserProfiler iup)
{
string username = iup.GetUserProfiler("fasdfasdfasdfas");
return "Welcome, " + username + "!";
}
}
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace WebApp2010
{
public interface IUserProfiler
{
string GetUserProfiler(string UserId);
}
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Security.Cryptography;
using System.Text;
using System.Threading.Tasks;
using WebApp2010;

namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
IUserProfiler iup = new UserProfilerService();
string name = iup.MyProfiler();
Console.Write(name);
string name1 = iup.GetUserProfiler("fasdfasdfasdfas");
Console.Write(name1);
string str1 = Console.ReadLine();

 假设有一种场景是我我无法修改接口和他的实现类，因为在某种情况下，如果接口的实现类很多的话，那么你就要一一修改实现类里面的代码。这个时候我们只需要扩展接口就可以很轻松的解决这件事情。