委派

     委托就像一個函數的指針，在程式運作時可以使用它們來調用不同的函數。委托存儲方法名，以及傳回值類型和參數清單。一個委派有兩個部分：委派類和類的委派對象。

     定義委派類，如 public delegate double DelegateCalculation(

　　　　double acceleration ,double time

     );

    然後可以建立一個委派對象

    DelegateCalculation myDelegateCalculation =

          new DelegateCalculation(MotionCalculations.FinalSpeed); 

   例如：

1 /*

2 Example12_1.cs illustrates the use of a delegate

3  */

4

5  using System;

6

7

8 // declare the DelegateCalculation delegate class

9 public delegate double DelegateCalculation(

10 double acceleration, double time

11 );

12

13

14 // declare the MotionCalculations class

15 public class MotionCalculations

16 {

17

18 // FinalSpeed() calculates the final speed

19 public static double FinalSpeed(

20 double acceleration, double time

21 )

22 {

23 double finalSpeed = acceleration * time;

24 return finalSpeed;

25 }

26

27 // Distance() calculates the distance traveled

28 public static double Distance(

29 double acceleration, double time

30 )

31 {

32 double distance = acceleration * Math.Pow(time, 2) / 2;

33 return distance;

34 }

35

36 }

37

38

39 class Example12_1

40 {

41

42 public static void Main()

43 {

44

45 // declare and initialize the acceleration and time

46 double acceleration = 10; // meters per second per second

47 double time = 5; // seconds

48 Console.WriteLine("acceleration = " + acceleration +

49 " meters per second per second");

50 Console.WriteLine("time = " + time + " seconds");

51

52 // create a delegate object that calls

53 // MotionCalculations.FinalSpeed

54 DelegateCalculation myDelegateCalculation =

55 new DelegateCalculation(MotionCalculations.FinalSpeed);

56

57 // calculate and display the final speed

58 double finalSpeed = myDelegateCalculation(acceleration, time);

59 Console.WriteLine("finalSpeed = " + finalSpeed +

60 " meters per second");

61

62 // set the delegate method to MotionCalculations.Distance

63 myDelegateCalculation =

64 new DelegateCalculation(MotionCalculations.Distance);

65

66 // calculate and display the distance traveled

67 double distance = myDelegateCalculation(acceleration, time);

68 Console.WriteLine("distance = " + distance + " meters");

69

70 }

71

72 }