C# 3.0中扩展方法怎么用

这篇文章主要介绍了C# 3.0中扩展方法怎么用，具有一定借鉴价值，感兴趣的朋友可以参考下，希望大家阅读完这篇文章之后大有收获，下面让小编带着大家一起了解一下。

Extension Methods 使用扩展方法，使用的时候需要注意的地方

1.C# 3.0新特性中扩展方法所属的类必须为静态非泛型类，扩展方法也是静态方法

2.***个参数为被扩展的类型实例，并且必须用this进行修饰

3.第二个参数开始对对应被扩展类型实例所传递的参数列表，即扩展类型实例

传递的***个参数对应扩展方法定义的第二个参数，依次类推

4.C# 3.0新特性中被扩展类型实例可像调用类型内部定义的实例方法一样调用扩展方法

这里定义一个扩展方法：

public static class Extensions      {          public static bool Compare(this Customer customer1, Customer customer2)          {              if (customer1.CustomerId == customer2.CustomerId &&                  customer1.Name == customer2.Name &&                  customer1.City == customer2.City)              {                  return true;              }               return false;          }       }

其中Compare***个参数用this修饰

完整源码例子，这个例子主要查询新建的newCustomer是否在列表List中

using System;  using System.Collections.Generic;  using System.Linq;  using System.Text;   namespace NewLanguageFeatures  {      public class Customer      {          public int CustomerId { get; private set; }           public string Name { get; set; }          public string City { get; set; }           public Customer(int Id)          {              CustomerId = Id;          }           public override string ToString()          {              return Name + "\t" + City + "\t" + CustomerId;          }      }      public static class Extensions      {          public static bool Compare(this Customer customer1, Customer customer2)          {              if (customer1.CustomerId == customer2.CustomerId &&                  customer1.Name == customer2.Name &&                  customer1.City == customer2.City)              {                  return true;              }               return false;          }       }       class Program      {          static void Main(string[] args)          {              var customers = CreateCustomers();               var newCustomer = new Customer(10)              {                  Name = "Stuart Glasson",                  City = "Oxford"              };               foreach (var c in customers)              {                        if (newCustomer.Compare(c))                  {                      Console.WriteLine("The new customer was already in the list");                      return;                  }               }               Console.WriteLine("The new customer was not in the list");           }           static List< Customer> CreateCustomers()          {              return new List< Customer>                  {                      new Customer(1) { Name = "Alex Roland",             City = "Berlin"    },                      new Customer(2) { Name = "Oliver Cox",              City = "Marseille" },                      new Customer(3) { Name = "Maurice Taylor",          City = "London"    },                      new Customer(4) { Name = "Phil Gibbins",            City = "London"    },                      new Customer(5) { Name = "Tony Madigan",            City = "Torino"    },                      new Customer(6) { Name = "Elizabeth A. Andersen",   City = "Portland"  },                      new Customer(7) { Name = "Justin Thorp",            City = "London"    },                      new Customer(8) { Name = "Bryn Paul Dunton",        City = "Portland"  }                  };          }      }

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