扩展方法

 public static class ExtendMethod
    {
        　public static int ToInt32Ext(this string s)
          {
             return Int32.Parse(s);
          }

         /// <summary>
         /// 实现自己的Foreach扩展方法
         /// </summary>
         /// <typeparam name="T"></typeparam>
         /// <param name="list"></param>
         /// <param name="action"></param>

         public static void ForEach123<T>(this List<T> list, Action<T> action)
         {
             foreach (T t in list)
                 action(t);
         }

    }

 调用：

        private void DoExtend()
        {
            string s = "9";
            int i = s.ToInt32Ext();
            List<string> ls = new List<string>() { "a", "b", "c" };
            ls.ForEach123(ss => MessageBox.Show(ss));

        }

 

被扩展对象：

     this 后面，跟的类型

委托定义：

      无返回参数 Action<T1,T2.....>

      有返回参数  Func< T1,T2,.....R>  R 返回类型