C#的delegate/event/Action/Func/Predicate關鍵字

回顧C#發展的曆史，C#1.0完全是模仿Java，并保留了C/C++的一些特性如struct，新學者很容易上手；C#2.0加入了泛型，也與 Java1.5的泛型如出一轍；C#3.0加入了一堆文法糖，并在沒有修改CLR的情況下引入了Linq，簡直是神來之筆，雖然很多項目出于各種各樣如性能之類的原因沒有采用，但非常适合小型程式的快速開發，減輕了程式員的工作量，也提高了代碼的可讀性；C#4.0增加了動态語言的特性，從裡面可以看到很多javascript、python這些動态語言的影子。雖然越來越偏離靜态語言的道路，但從另一個角度來說，這些特性也都是為了提高程式員的生産力。至于被接受與否，還是讓時間來說話吧。

好了，看看C#的delegate/event/Action/Func/Predicate關鍵字，直接上代碼：

1:  using System;      

2:  using System.Collections.Generic;      

3:  using System.Linq;      

4:  using System.Text;      

5:         

6:  namespace ConsoleApplication1      

7:  {      

8:      class Program      

9:      {      

10:          public class Test      

11:          {      

12:              public delegate void WriteName(string name);  //定義委托      

13:              public static event WriteName WriteNameEvent; //定義事件      

14:          }      

15:         

16:          static Action<string> WriteNameAction;//Action是參數從0到4，傳回類型為void(即沒有傳回值)的委托      

17:          static Func<string, int> WriteNameFunction;//Func的參數從1到5個，有傳回值的委托，最後一個是傳回類型      

18:               

19:          static void Main(string[] args)      

20:          {      

21:              Test.WriteName myDelegate = x => { Console.WriteLine("abc,{0}！", x); }; // 使用 Lambda 表達式      

22:              myDelegate("teststring");      

23:         

24:              Test.WriteName w = (string name) => { Console.WriteLine("Hello,{0}！", name); };//使用匿名委托      

25:              w("Jimmy");      

26:         

27:              Test.WriteNameEvent += (string name) => { Console.WriteLine("Hello,{0}！", name); };//使用匿名委托      

28:              Test.WriteNameEvent += delegate(string name) { Console.Write("test"); }; //使用匿名方法(.net 2.0)      

29:         

30:              WriteNameAction = HelloWrite; // 匿名委托，和這個一樣：WriteNameAction = new Action<string>(HelloWrite);      

31:              WriteNameAction("test");      

32:         

33:              WriteNameAction = (string name) => { Console.WriteLine("hello，{0}！", name); };//使用匿名委托      

34:              WriteNameAction("test2");      

35:         

36:         

37:              WriteNameFunction = HelloWrite2; // 匿名委托，和這個一樣：WriteNameFunction = new Func<string, int>(HelloWrite2);      

38:              Console.WriteLine(WriteNameFunction("test3"));      

39:         

40:              Predicate<int[]> preTest = i => i.Length == 10;      

41:         

42:              Console.Read();      

43:         

44:          }      

45:         

46:          static List<String> listString = new List<String>()      

47:          {      

48:              "One","Two","Three","Four","Fice","Six","Seven","Eight","Nine","Ten"      

49:          };      

50:         

51:          static List<String> GetFirstStringFromList()      

52:          {      

53:              string str = GetStringList(a => { return a.Length <= 3 && a.Contains('S'); });// 使用 Predicate 泛型委托      

54:         

55:              return listString.FindAll((c) => { return c.Length <= 3; });// 使用 Predicate 泛型委托      

56:          }      

57:         

58:          static String GetStringList(Predicate<String> p) // 使用 Predicate 泛型委托      

59:          {      

60:              foreach (string item in listString)      

61:              {      

62:                  if (p(item))      

63:                      return item;      

64:              }      

65:              return null;      

66:          }      

67:         

68:          static void HelloWrite(string name)      

69:          {      

70:              Console.WriteLine("Hello world,{0}！", name);      

71:          }      

72:         

73:          static int HelloWrite2(string name)      

74:          {      

75:              Console.WriteLine("Hello world,{0}！", name);      

76:              return 1;      

77:          }      

78:      }      

79:  }