ex-12-01

Programming Csharp Source Code(代码) Programming Csharp Source Code

// Example 12-01: Working with delegates

namespace Programming_CSharp
{
   using System;

   public enum comparison
   {
      theFirstComesFirst = 1,
      theSecondComesFirst = 2
   }

   // a simple collection to hold 2 items
   public class Pair
   {
      // the delegate declaration
      public delegate comparison 
         WhichIsFirst(object obj1, object obj2);

      // passed in constructor take two objects, 
      // added in order received
      public Pair(
         object firstObject, 
         object secondObject)
      {
         thePair[0] = firstObject;
         thePair[1] = secondObject;
      }

      // public method which orders the two objects
      // by whatever criteria the object likes!
      public void Sort(
         WhichIsFirst theDelegatedFunc)
      {
         if (theDelegatedFunc(thePair[0],thePair[1]) 
            == comparison.theSecondComesFirst)
         {
            object temp = thePair[0];
            thePair[0] = thePair[1];
            thePair[1] = temp;
         }
      }

      // public method which orders the two objects
      // by the reverse of whatever criteria the object likes!
      public void ReverseSort(
         WhichIsFirst theDelegatedFunc)
      {
         if (theDelegatedFunc(thePair[0],thePair[1]) == 
            comparison.theFirstComesFirst)
         {
            object temp = thePair[0];
            thePair[0] = thePair[1];
            thePair[1] = temp;
         }
      }

      // ask the two objects to give their string value
      public override string ToString()
      {
         return thePair[0].ToString() + ", " 
            + thePair[1].ToString();
      }


      // private array to hold the two objects
      private object[] thePair = new object[2];  
   }

   public class Dog
   {
      public Dog(int weight)
      {
         this.weight=weight;
      }

      // dogs are ordered by weight
      public static comparison WhichDogComesFirst(
         Object o1, Object o2)
      {
         Dog d1 = (Dog) o1;
         Dog d2 = (Dog) o2;
         return d1.weight > d2.weight ? 
            comparison.theSecondComesFirst : 
            comparison.theFirstComesFirst;
      }
      public override string ToString()
      {
         return weight.ToString();
      }
      private int weight;
   }

   public class Student
   {
      public Student(string name)
      {
         this.name = name;
      }

      // students are ordered alphabetically
      public static comparison 
         WhichStudentComesFirst(Object o1, Object o2)
      {
         Student s1 = (Student) o1;
         Student s2 = (Student) o2;
         return (String.Compare(s1.name, s2.name) < 0 ? 
            comparison.theFirstComesFirst : 
            comparison.theSecondComesFirst);
      }

      public override string ToString()
      {
         return name;
      }
      private string name;
   }

   public class Test
   {
      public static void Main()
      {
         // create two students and two dogs
         // and add them to Pair objects
         Student Jesse = new Student("Jesse");
         Student Stacey = new Student ("Stacey");
         Dog Milo = new Dog(65);
         Dog Fred = new Dog(12);

         Pair studentPair = new Pair(Jesse,Stacey);
         Pair dogPair = new Pair(Milo, Fred);
         Console.WriteLine("studentPair\t\t\t: {0}", 
            studentPair.ToString());
         Console.WriteLine("dogPair\t\t\t\t: {0}", 
            dogPair.ToString());

         // Instantiate  the delegates
         Pair.WhichIsFirst  theStudentDelegate = 
            new Pair.WhichIsFirst(
            Student.WhichStudentComesFirst);

         Pair.WhichIsFirst theDogDelegate =
            new Pair.WhichIsFirst(
            Dog.WhichDogComesFirst);

         // sort using the delegates
         studentPair.Sort(theStudentDelegate);
         Console.WriteLine("After Sort studentPair\t\t: {0}", 
            studentPair.ToString());
         studentPair.ReverseSort(theStudentDelegate);
         Console.WriteLine("After ReverseSort studentPair\t: {0}", 
            studentPair.ToString());
            
         dogPair.Sort(theDogDelegate);
         Console.WriteLine("After Sort dogPair\t\t: {0}", 
            dogPair.ToString());
         dogPair.ReverseSort(theDogDelegate);
         Console.WriteLine("After ReverseSort dogPair\t: {0}", 
            dogPair.ToString());
      }
   }
}