1:      class CollectionInitializer : AppRunner.AbstractApplication

   2:      {

   3:          class StringCollection : ICollection<string>

   4:          {

   5:              public void Add(string item)

   6:              {

   7:                  Console.WriteLine(item);

   8:              }

   9:   

  10:              // Other ICollection<T> Members

  11:          }

  12:   

  13:          public override void Run()

  14:          {

  15:              StringCollection strings = new StringCollection() { "Van's", "Brog", "Vicky" };

  16:          }

  17:      }

　　在这个示例中，编译器会自动为strings对象调用Add方法，以将初始值列表中的所有元素加入到集合中，这里我们只是简单将初始值列表中的元素输出到控制台。

第六个特性：Lambda表达式

　　C# 2.0中加入的匿名代理，简化了我们编写事件处理函数的工作，使我们不再需要单独声明一个函数来与事件绑定，只需要使用delegate关键字在线编写事件处理代码。

　　而C# 3.0则更进一步，通过Lambda表达式，我们可以一种更为简洁方式编写事件处理代码，新的Lambda事件处理代码看上去就像一个计算表达式，它使用"=>"符号来连接事件参数和事件处理代码。我可以这样写：SomeEvent += 事件参数 => 事件处理代码;下面是完整的示例：

   1:      delegate T AddDelegate<T>(T a, T b);

   2:   

   3:      class LambdaExpression : AppRunner.AbstractApplication

   4:      {

   5:          public static event EventHandler MyEvent;

   6:   

   7:          public override void Run()

   8:          {

   9:              MyEvent += delegate(object s, EventArgs e)

  10:              {

  11:                  Console.WriteLine(s);

  12:              };

  13:   

  14:              MyEvent += (s, e) => { Console.WriteLine(s); };

  15:              

  16:              MyEvent(this, null);

  17:   

  18:              AddDelegate<string> add = (a, b) => a + b;

  19:   

  20:              Console.WriteLine(add("Lambda", "Expression"));

  21:          }

  22:      }

　　在上面的例子中，分别使用了匿名代理和Lambda表达式来实现同样的功能，可以明显看出Lambda表达式的实现更为简洁。我们在使用Lambda表达式编写事件处理代码时，无需指明事件参数的类型，且返回值就是最后一条语句的执行结果。

   1:      static class Extensions

   2:      {

   3:          public static int ToInt32(this string source)

   4:          {

   5:              return Int32.Parse(source);

   6:          }

   7:   

   8:          public static T[] Slice<T>(this T[] source, int index, int count)

   9:          {

  10:              if (index < 0 || count < 0 || index + count > source.Length)

  11:              {

  12:                  throw new ArgumentException();

  13:              }

  14:   

  15:              T[] result = new T[count];

  16:              Array.Copy(source, index, result, 0, count);    

  17:              return result;

  18:          }

  19:      }

  20:   

  21:      class ExtensionMethods : AppRunner.AbstractApplication

  22:      {

  23:          public override void Run()

  24:          {

  25:              string number = "123";

  26:              Console.WriteLine(number.ToInt32());

  27:   

  28:              int[] intArray = new int[] { 1, 2, 3 };

  29:   

  30:              intArray = intArray.Slice(1, 2);

  31:   

  32:              foreach (var i in intArray)

  33:                  Console.WriteLine(i);

  34:          }

  35:      }

   1:      class LinqExpression : AppRunner.AbstractApplication

   2:      {

   3:          public override void Run()

   4:          {

   5:              // 定义匿名数组persons, 并为其赋初值

   6:              var persons = new[] {

   7:                  new { Name="Van's", Sex=false, Age=22 },

   8:                  new { Name="Martin", Sex=true, Age=30 },

   9:                  new { Name="Jerry", Sex=false, Age=24 },

  10:                  new { Name="Brog", Sex=false, Age=25 },

  11:                  new { Name="Vicky", Sex=true, Age=20 }

  12:              };

  13:   

  14:   

  15:              /*

  16:                  执行简单Linq查询

  17:   

  18:                  检索所有年龄在24岁以内的人

  19:                  查询结果放在results变量中

  20:  

  21:                  results变量的类型与数组persons相同                

  22:              */

  23:              var results = from p in persons

  24:                            where p.Age <= 24

  25:                            select p;

  26:   

  27:              foreach (var person in results)

  28:              {

  29:                  Console.WriteLine(person.Name);

  30:              }

  31:   

  32:              Console.WriteLine();

  33:   

  34:   

  35:              // 定义匿名数组customers, 并为其赋初值

  36:              // 该数组是匿名类型的

  37:              var customers = new[] {

  38:                  new {

  39:                      Name="Van's", City="China", Orders=new[] {

  40:                          new {

  41:                              OrderNo=0,

  42:                              OrderName="C# Programming Language(Second Edition)",

  43:                              OrderDate=new DateTime(2007,9, 5)

  44:                          },

  45:                          new {

  46:                              OrderNo=1,

  47:                              OrderName="Head First Design Patterns(Chinese Edition)",

  48:                              OrderDate=new DateTime(2007,9,15)

  49:                          },

  50:                          new {

  51:                              OrderNo=2,

  52:                              OrderName="ASP.NET Unleashed 2.0(Chinese Edition)",

  53:                              OrderDate=new DateTime(2007,09,18)

  54:                          },

  55:                          new {

  56:                              OrderNo=3,

  57:                              OrderName="The C++ Programming Langauge(Special Edition)",

  58:                              OrderDate=new DateTime(2002, 9, 20)

  59:                          }

  60:                      }

  61:                  },

  62:                  new {

  63:                      Name="Brog", City="China", Orders=new[] {

  64:                          new {

  65:                              OrderNo=0,

  66:                              OrderName="C# Programming Language(Second Edition)",

  67:                              OrderDate=new DateTime(2007, 9, 15)

  68:                          }

  69:                      }

  70:                  },

  71:                  new {

  72:                      Name="Vicky", City="London", Orders=new[] {

  73:                          new { OrderNo=0,

  74:                              OrderName="C++ Programming Language(Special Edition)",

  75:                              OrderDate=new DateTime(2007, 9, 20)

  76:                          }

  77:                      }

  78:                  }

  79:              };

  80:   

  81:   

  82:              /*

  83:                  执行多重Linq查询

  84:   

  85:                  检索所在城市为中国, 且订单日期为2007年以后的所有记录

  86:                  查询结果是一个匿名类型的数组

  87:                  其中包含客户名, 订单号, 订单日期, 订单名四个字段

  88:              */

  89:              var someCustomers = from c in customers

  90:                                  where c.City == "China"

  91:                                  from o in c.Orders

  92:                                  where o.OrderDate.Year >= 2007

  93:                                  select new { c.Name, o.OrderNo, o.OrderDate, o.OrderName };

  94:   

  95:   

  96:              foreach (var customer in someCustomers)

  97:              {

  98:                  Console.WriteLine(

  99:                      customer.Name + ", " + customer.OrderName + ",  " +

 100:                      customer.OrderDate.ToString("D")

 101:                  );

 102:              }

 103:          }

 104:      }

　　从上面的例子中，我们可以看到Linq查询的强大特性，它允许我们进行简单查询，或者进行更为复杂的多重连接查询。且查询的结果还可以是自定义的匿名类型。

　　以上是对C# 3.0中新增的八大特性的简要介绍，如果想了解更为深入的内容，可查看C# 3.0的官方规范。

相关文章：C#3.0 新特性速览(1)

   1:      class LocalVariables : AppRunner.AbstractApplication

   2:      {

   3:          public override void Run()

   4:          {

   5:              var intValue = 5;

   6:              var stringValue = "This is a string";

   7:              var customClass = new LocalVariables();

   8:              var intArray = new int[3] { 1, 2, 3 };

   9:   

  10:              foreach (var value in intArray)

  11:                  Console.WriteLine(value);            

  12:          }

  13:      }

   1:      class LocalVariables : AppRunner.AbstractApplication

   2:      {

   3:          public override void Run()

   4:          {

   5:              int intValue = 5;

   6:              string stringValue = "This is a string";

   7:              LocalVariables customClass = new LocalVariables();

   8:              int[] intArray = new int[3];

   9:   

  10:              foreach (int value in intArray)

  11:                  Console.WriteLine(value);            

  12:          }

  13:      }

   1:      class AnonymousType : AppRunner.AbstractApplication

   2:      {

   3:          public override void Run()

   4:          {

   5:              var anonymousType1 = new {
   6:                  CardNumber = "10001", Name = "van's", Sex = true

   7:              };

   8:   

   9:              Console.WriteLine(anonymousType1.CardNumber);

  10:              Console.WriteLine(anonymousType1.Name);

  11:   

  12:              var anonymousType2 = new {

  13:                  CardNumber = "10002", Name = "martin", Sex = true

  14:              };

  15:   

  16:              anonymousType2 = anonymousType1;

  17:          }

  18:      }

    1:      class AnonymousTypeArray : AppRunner.AbstractApplication

   2:      {

   3:          public override void Run()

   4:          {

   5:              var intArray = new[] { 1, 2, 3, 4, 5 };

   6:              var doubleArray = new[] { 3.14, 1.414 };

   7:              var anonymousTypeArray = new[] {

   8:                  new { Name="van's", Sex=false, Arg=22 },

   9:                  new { Name="martin", Sex=true, Arg=23 }

  10:              };

  11:   

  12:              Console.WriteLine(intArray);

  13:              Console.WriteLine(doubleArray);

  14:              Console.WriteLine(anonymousTypeArray[0].Name);

  15:          }

  16:      }

　　上面的代码中，anonymousTypeArray变量的声明同时运用了隐式类型化数组和匿名类型两种特性，首先创建匿名类型，然后再初始值列表，推断出数组的确切类型。

第四个特性：对象构造者

　　我们在声明数组时，可以同时对其进行初始化，这样就省去了很多麻烦，但是在创建类的对象时，这招可就不灵了，我们要么调用该类的构造函数完成对象的初始化，要么就手工进行初始化。这两种方法都不太方便，使用构造函数来对对象进行初始化时，我们为了某种灵活性，可能需要编写构造函数的多个重载版本，实在是麻烦。

　　C#3.0中加入的对象构造者特性，使得对象的初始化工作变得格外简单，我们可以采用类似于数组初始化的方式来初始化类的对象，方法就是直接在创建类对象的表达式后面跟上类成员的初始化代码。具体示例如下：

   1:     class Point

   2:     {

   3:          public int X { get; set; }

   4:          public int Y { get; set; }

   5:   

   6:          public override string ToString()

   7:          {

   8:              return "(" + X.ToString() + ", " + Y.ToString() + ")";

   9:          }

  10:      }

  11:   

  12:      class Rectangle

  13:      {

  14:          public Point P1 { get; set; }

  15:          public Point P2 { get; set; }

  16:   

  17:          public Rectangle()

  18:          {

  19:              P1 = new Point();

  20:              P2 = new Point();

  21:          }

  22:   

  23:          public override string ToString()

  24:          {

  25:              return "P1: " + P1 + ", P2: " + P2;

  26:          }

  27:      }

  28:   

  29:      class ObjectBuilder : AppRunner.AbstractApplication

  30:      {

  31:          public override void Run()

  32:          {

  33:              Point thePoint = new Point() { X = 1, Y = 2 };

  34:              Console.WriteLine("Point(X, Y) = {0}", thePoint);

  35:   

  36:              Rectangle theRectangle = new Rectangle() { 

  37:                  P1 = { X = 1, Y = 1 }, P2 = { X = 100, Y = 200 } 

  38:              };

  39:              Console.WriteLine(theRectangle);

  30:          }

  41:      }

　　我们在定义Point类的X和Y属性时，只须写上该属性的get和set访问器声明，C#编译器会自动为我们生成默认的get和set操作代码，当我们需要定义简单属性时，这个特性非常有用。

　　我们以new Point() { X = 1, Y = 2 }语句，轻松的完成了对Point类的初始化工作。在创建类的对象时，我们可以按照需要去初始化类的对象，只要在类的创建表达式后跟上要初始化属性的列表即可，且可以只对需要初始化的属性赋初值，而无需把所有属性的初始值都写上去。

　　在theRectangle对象的初始化表达式中，我们首先对P1属性进行初始化，然而P1属性也是一个自定义的类型，所以P1属性的初始化是另一个类型(Point)的初始化表达式，我们可以这样的方式来对更加复杂的类型进行初始化。

　　未完待续.........

相关文章：C#3.0 新特性速览(2)

刚装上了Windows Live Writer，现发篇文章测试一下。

Code test

   1:  using System;

   2:   

   3:  class Program

   4:  {

   5:      static void Main(string[] args)

   6:      {

   7:          Console.WriteLine("Hello world from C#!");

   8:      }

   9:  }

Text test

Normal, Bold, Italic, Underline

Blockquote test

This is a text

Image test

Link test

My Blog Address