Delegates And Events
/*
Learning C#
by Jesse Liberty
Publisher: O'Reilly
ISBN: 0596003765
*/
using System;
namespace DelegatesAndEvents
{
public enum comparison
{
theFirstComesFirst = 1,
theSecondComesFirst = 2
}
// A simple collection to hold two items
class Pair
{
// Private array to hold the two objects
private object[] thePair = new object[2];
// The delegate declaration
public delegate comparison
WhichIsFirst(object obj1, object obj2);
// Passed in constructor takes two objects,
// added in order received
public Pair(
object firstObject,
object secondObject)
{
thePair[0] = firstObject;
thePair[1] = secondObject;
}
// Public method that orders the
// two objects by whatever criteria the objects like!
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 that orders the
// two objects by the reverse of whatever criteria the
// objects 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();
}
}
class Dog
{
private int weight;
public Dog(int weight)
{
this.weight=weight;
}
// dogs are sorted 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();
}
}
class Student
{
private string name;
public Student(string name)
{
this.name = name;
}
// Students are sorted 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;
}
}
public class TesterDelegatesAndEvents11
{
public void Run()
{
// 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());
}
static void Main()
{
TesterDelegatesAndEvents11 t = new TesterDelegatesAndEvents11();
t.Run();
}
}
}
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