風影ASP.NET基礎教學 13 NET3.0特性補充

static  class Helper {

      public static T Cast<T>(this object obj, T sample)

      { 

          //類型推導功能

          return (T)obj;

      }

  }

  public static class Helper2

  {

      public static string ShowTime(this String obj)

      {

          return obj + DateTime.Now.ToString();

      }

  }

    class Program

    {

        static void Main(string[] args)

        {

            #region 匿名型別的局部變數

            //var str = "Hello";

            //var num = 22.3;

            //var arr = new[] { "1", "2", "3" };

            //foreach (var item in arr)

            //{

            //    Console.WriteLine(item);

            //}

            #endregion

            #region 匿名型別

            //var Test = new { name = "zhangsan", id = 12 };

            //Console.WriteLine(Test.name);

            #endregion

            #region 擴充方法

            //var abc = "hello".ShowTime();

            //Console.WriteLine(abc);

            #endregion

            #region 對象初始化器

            #endregion

            #region 集合初始化器

            List<String> list = new List<string>() { "1","3","ggf"};

            foreach (var item in list)

            {

                Console.WriteLine(item);

            }

            #endregion

            #region Lambda運算式

            //所謂Lambda運算式實際上是對一個集合進行資料篩選和計算用的

            List<object> user = new List<object>{

    new {Id=1,Name="YJingLee",Age=22},

    new {Id=2,Name="XieQing",Age=25},

};

            //擷取特定人時所用的過濾條件，p參數屬於User類型

            var results = user.Where(p => p.Cast(new { Id = 0, Name = string.Empty, Age = 0 }).Name == "XieQing").ToList();

            foreach (var item in results)

            {

                Console.WriteLine(item.Cast(new { Id = 0, Name = "", Age = 0 }).Name);

            }

            //用User對象的Age值計算平均年齡

            var average = user.Average(p => p.Cast(new { Id = 0, Name =string.Empty, Age = 0 }).Age);

            #endregion

        }

    }