.Net 4.0 新特性

A.dynamic

 1  public class dynamicDemo
 2    {  
 3        public static void Test()
 4        {
 5         dynamic d = 100;
 6         d += 10;
 7         Console.WriteLine(d.GetType()+"    +=10 Result:\t"+d);
 8         d = 1.200;
 9         d += 10;
10         Console.WriteLine(d.GetType() + "   +=10 Result:\t" + d);
11         d = "string";
12         d += 10;
13         Console.WriteLine(d.GetType() + "   +=10 Result:\t" + d);
14        }
15 }

B.可选（或默认）参数 ,命名参数

   public class DefaultParmDemo
    {
        //可选（或默认）参数:y/z
       public void Add(int x, int y = 10, int z = 100)
       {
          Console.WriteLine(string.Format("x({0})+y({1})+z({2})=Sum({3})",x,y,z,x+y+z));
       }
     
       public static void Test()
       {
           DefaultParmDemo demo=new DefaultParmDemo();
           demo.Add(5);
           demo.Add(5, 5);
           demo.Add(5, z: 10);
           demo.Add(5, z: 10, y: 15);
          //命名参数：方法定义的参数顺序与方法调用时的参数顺序可以不一致
       }
    }

C.Lazy<T>

[使用场景]
i.当创建一个对象的子对象开销比较大时，而且有可能在程序中用不到这个子对象，
那么可以考虑用延迟加载的方式来创建子对象。
ii.另外一种情况就是当程序一启动时，需要创建多个对象，但仅有几个对象需要立即使用，
这样就可以将一些不必要的初始化工作延迟到使用时，这样可以非常有效的提高程序的启动速度。

DataExample:

View Code

 1 public class DataExample
 2 {
 3     public string Title
 4     {
 5         get;
 6         set;
 7     }
 8     public static List<DataExample> GetExampleList()
 9     {
10         List<DataExample> examples = new List<DataExample> {            
11             new DataExample{Title="Lazy Load"},
12             new DataExample{Title="Delegate"},
13             new DataExample{Title="Event"},
14             new DataExample{Title="Thread"}
15             };
16         return examples;
17     }
18     public static List<Lazy<DataExample>> GetLazyExampleList()
19     {
20         List<Lazy<DataExample>> examples=new List<Lazy<DataExample>>{            
21             new Lazy<DataExample>(()=>new DataExample{Title="Lazy Load"}),
22             new Lazy<DataExample>(()=> new DataExample{Title="Delegate"}),
23             new Lazy<DataExample>(()=>new DataExample{Title="Event"}),
24             new Lazy<DataExample>(()=>new DataExample{Title="Thread"})
25         };
26        return examples;
27     }
28 }

 1 public  class LazyDemo
 2  {
 3       
 4         public Lazy<List<DataExample>> DataExampleA
 5         {
 6             get;
 7             private set;
 8         }
 9         public List<Lazy<DataExample>> DataExampleB
10         {
11             get;
12             private set;
13         }
14         
15         // 第一次引用时加载
16         private List<DataExample> _dataExampleC;
17         public List<DataExample> DataExampleC
18         {
19             get
20             {
21                 if (_dataExampleC==null)
22                 {
23                     _dataExampleC = DataExample.GetExampleList();
24                 }
25                 return _dataExampleC;
26             }
27         }
28         public LazyDemo()
29         {
30             
31             //多个对象不一定都用到时
32             DataExampleA = new Lazy<List<DataExample>>(
                              () => DataExample.GetExampleList());        
33             DataExampleB = DataExample.GetLazyExampleList();
34             
35            
36         }
37         public override string ToString()
38         {
39           
40             Console.WriteLine("A IsValueCreated:"
                             +DataExampleA.IsValueCreated);
41             int i=0;
42             foreach (var item in this.DataExampleB)
43             {   
44                 Console.WriteLine("B Item IsCreated: " 
                      +item.IsValueCreated+"\tTitle:"+item.Value.Title);                 
45                 if (i++>0)
46                     break;
47             }
48             Console.WriteLine();
49             foreach (var item in this.DataExampleB)
50             {
51                 Console.WriteLine("B Item IsCreated: " + item.IsValueCreated
                       + "\tTitle:" + item.Value.Title);   
52             }
53 
54             Console.WriteLine("A IsValueCreated:"
                             +DataExampleA.IsValueCreated);
55             return base.ToString();
56         }
57 
58         public static void Test()
59         {
60             //延迟加载
61             LazyDemo blogUser = new LazyDemo();
62             blogUser.ToString();
63         }
64     }