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2010-05-26T16:40:06Z

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2010-05-26T12:42:30Z

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==Delegate Demo for a Simple Class==

<source lang="vbnet">
Imports System
Imports System.Diagnostics
Public Class MainClass
Private Delegate Function NumEmployeesDelegate() As Integer
Shared Sub Main()
Dim emp As New Employee("Rod", "Stephens")
Dim show_num As NumEmployeesDelegate

show_num = AddressOf Employee.GetNumEmployees
Console.WriteLine(show_num().ToString)

End Sub
End Class

Public Class Employee
" In a real application, this would return
" some sort of array or collection"s size.
Public Shared Function GetNumEmployees() As Integer
Return 13
End Function
" The Employee"s first name.
Private m_FirstName As String = "<first name>"
Public Property FirstName() As String
Get
Return m_FirstName
End Get
Set(ByVal value As String)
m_FirstName = value
End Set
End Property
" The Employee"s last name.
Private m_LastName As String = ""
Public Property LastName() As String
Get
Return m_LastName
End Get
Set(ByVal value As String)
m_LastName = value
End Set
End Property
Public Sub New(ByVal first_name As String, ByVal last_name As String)
m_FirstName = first_name
m_LastName = last_name
End Sub
Public Overrides Function ToString() As String
Return m_FirstName & " " & m_LastName
End Function
End Class

</source>

==Delegate Syntax==

<source lang="vbnet">
Option Strict On
Imports System.Collections.Generic
Module Program
Sub Main()
Dim list As New List(Of Integer)()
list.AddRange(New Integer() {20, 1, 4, 8, 9, 44})
Dim callback As New Predicate(Of Integer)(AddressOf IsEvenNumber)
Dim evenNumbers As List(Of Integer) = list.FindAll(callback)
For Each evenNumber As Integer In evenNumbers
Console.WriteLine(evenNumber)
Next
End Sub
Function IsEvenNumber(ByVal i As Integer) As Boolean
Return (i Mod 2) = 0
End Function
End Module

</source>

==Delegate with and without parameters==

<source lang="vbnet">
Imports System
Imports System.Collections

Delegate Sub DelegateWithStringSignature(ByVal S As String)
Delegate Sub DelegateWithNoParam()
public class MainClass
Shared Sub Main()
Dim c As New CalledClass()
Dim o As New OtherCalledClass()
Dim BadObject As New ObjectWithNoWriteMessage()
Dim d1 As DelegateWithStringSignature
Dim Params() As Object = {"DynamicParam"}
" The two following lines are identical
d1 = New DelegateWithStringSignature(AddressOf c.WriteMessage)
d1.Invoke("Test")
d1.DynamicInvoke(Params)
d1 = AddressOf c.WriteMessage
d1.Invoke("Test")
d1.DynamicInvoke(Params)
End Sub
End Class
Class CalledClass
Shared Sub SharedMessage(ByVal s As String)
Console.WriteLine("CalledClass.SharedMessage with parameter: " & s)
End Sub
Public Sub WriteMessage(ByVal s As String)
Console.WriteLine("CalledClass WriteMessage method with parameter: " & s)
End Sub
End Class
Class OtherCalledClass
Sub WriteMessage(ByVal s As String)
Console.WriteLine("OtherCalledClass WriteMessage method with parameter: " & s)
End Sub
End Class
Class ObjectWithNoWriteMessage
Sub BadWriteMessage()
End Sub
End Class

</source>

==Function Delegate: output string==

<source lang="vbnet">
Imports System
Public Class MainClass
" delegate to be a pointer to a subroutine
" that has a string parameter.
Private Delegate Sub StringDisplayerType(ByVal str As String)
Shared Sub Main(ByVal args As String())
Dim m_DisplayStringRoutine As StringDisplayerType
" Assign the variable to a subroutine.
m_DisplayStringRoutine = AddressOf ShowStringInMessageBox
" Invoke the delegate"s subroutine.
m_DisplayStringRoutine("Hello world")

m_DisplayStringRoutine = AddressOf ShowStringInOutputWindow
" Invoke the delegate"s subroutine.
m_DisplayStringRoutine("Hello world")

End Sub
Shared Private Sub ShowStringInOutputWindow(ByVal str As String)
Console.WriteLine(str)
End Sub
Shared Private Sub ShowStringInMessageBox(ByVal str As String)
Console.WriteLine(str)
End Sub
End Class

</source>

==Function Delegation Demo==

<source lang="vbnet">
Imports System
Public Class MainClass
Dim emp As New Employee("First Name", "Last Name")
Private Delegate Function NumEmployeesDelegate() As Integer
Shared Sub Main(ByVal args As String())
Dim show_num As NumEmployeesDelegate
show_num = AddressOf Employee.GetNumEmployees

Console.WriteLine(show_num().ToString)
End Sub
End Class

Public Class Employee
Private m_FirstName As String
Private m_LastName As String
Private Shared m_NumEmployees As Integer = 0
Public Shared Function GetNumEmployees() As Integer
Return m_NumEmployees
End Function
Public Sub New(ByVal first_name As String, ByVal last_name As String)
m_FirstName = first_name
m_LastName = last_name
m_NumEmployees += 1
End Sub
Public Overrides Function ToString() As String
Return m_FirstName & " " & m_LastName
End Function
Private disposedValue As Boolean = False " To detect redundant calls
End Class

</source>

==Multicast Delegate==

<source lang="vbnet">
Imports System
Public Class MainClass
Shared Sub Main( )
Dim Writer, Logger As _
MyClassWithDelegate.StringDelegate
Dim myMulticastDelegate As MyClassWithDelegate.StringDelegate
Writer = New MyClassWithDelegate.StringDelegate( _
AddressOf MyImplementingClass.WriteString)
Logger = New MyClassWithDelegate.StringDelegate( _
AddressOf MyImplementingClass.LogString)
Dim arr( ) As MyClassWithDelegate.StringDelegate = _
{Writer, Logger}
Writer("String passed to Writer" & vbCrLf)
Logger("String passed to Logger" & vbCrLf)
Console.WriteLine(vbCrLf & "myMulticastDelegate = " + _
"Writer and Logger")
myMulticastDelegate = _
DirectCast(System.Delegate.rubine(arr), _
MyClassWithDelegate.StringDelegate)
myMulticastDelegate("First string passed to Collector")
Console.WriteLine(vbCrLf & _
"myMulticastDelegate Adds Transmitter")

Console.WriteLine(vbCrLf & "myMulticastDelegate -= Logger")
myMulticastDelegate = _
DirectCast(System.Delegate.Remove(myMulticastDelegate, _
Logger), MyClassWithDelegate.StringDelegate)
myMulticastDelegate("Third string passed to Collector")

End Sub "Main

End Class
Public Class MyClassWithDelegate
Public Delegate Sub StringDelegate(ByVal s As String)
End Class
Public Class MyImplementingClass
Public Shared Sub WriteString(ByVal s As String)
Console.WriteLine("Writing string {0}", s)
End Sub
Public Shared Sub LogString(ByVal s As String)
Console.WriteLine("Logging string {0}", s)
End Sub
End Class

</source>

==Register Delegates and call them==

<source lang="vbnet">
Imports System
Public Class MainClass
Public Delegate Sub CallBackFunc()
Private Shared m_cbFunc As CallBackFunc
Public Shared Sub Main()
RegisterDelegate(AddressOf CallBackHandler1)
RegisterDelegate(AddressOf CallBackHandler2)
CallDelegates()
End Sub
Shared Public Sub CallBackHandler1()
Console.WriteLine("Callback 1 returned ")
End Sub
Shared Public Sub CallBackHandler2()
Console.WriteLine("Callback 2 returned ")
End Sub
Shared Public Sub RegisterDelegate(ByRef cbFunc As CallBackFunc)
m_cbFunc = CType(System.Delegate.rubine(m_cbFunc, cbFunc), CallBackFunc)
End Sub

Shared Public Sub CallDelegates()
m_cbFunc()
End Sub
End Class

</source>

==Simple Delegate Demo==

<source lang="vbnet">
Imports System
Public Class MainClass
Public Delegate Sub StringSubDelegate(ByVal aString As String)
Shared Sub Main()
Dim test As New ClassForStringSubDelegate()
Dim aDelegate As StringSubDelegate
aDelegate = AddressOf test.TestSub
aDelegate("Hello")

aDelegate = AddressOf test.TestMsgBox
aDelegate("Hello")

End Sub
End Class
Public Class ClassForStringSubDelegate
Public Sub TestSub(ByVal aString As String)
Console.WriteLine(aString & aString)
End Sub
Public Sub TestMsgBox(ByVal aString As String)
Console.WriteLine("I am in a Message Box" & aString)
End Sub
End Class

</source>

==Sort Delegate==

<source lang="vbnet">
Imports System
Public Class MainClass
Shared Dim mBubbleSort As New CDelegateBubbleSort()
Shared Dim mElementArray As Integer() = New Integer(9) {}

Shared Sub Main(ByVal args As String())
Dim randomNumber As Random = New Random()
Dim i As Integer
Console.WriteLine("Init Value:")
" create String with 10 random numbers
For i = 0 To mElementArray.GetUpperBound(0)
mElementArray(i) = randomNumber.Next(100)
Console.WriteLine( mElementArray(i) )
Next
mBubbleSort.SortArray(mElementArray, AddressOf SortAscending)
Console.WriteLine("Sort Ascending")
For i = 0 To mElementArray.GetUpperBound(0)
Console.WriteLine( mElementArray(i) )
Next
mBubbleSort.SortArray(mElementArray, AddressOf SortDescending)
Console.WriteLine("Sort Descending")
For i = 0 To mElementArray.GetUpperBound(0)
Console.WriteLine( mElementArray(i) )
Next
End Sub

" delegate implementation sorts in asending order
Shared Private Function SortAscending(ByVal element1 As Integer, _
ByVal element2 As Integer) As Boolean
Return element1 > element2
End Function " SortAscending
" delegate implementation sorts in descending order
Shared Private Function SortDescending(ByVal element1 As Integer, _
ByVal element2 As Integer) As Boolean
Return element1 < element2
End Function " SortDescending
End Class

Public Class CDelegateBubbleSort
Public Delegate Function Comparator( _
ByVal element1 As Integer, _
ByVal element2 As Integer) As Boolean
Public Sub SortArray(ByVal array As Integer(), _
ByVal Compare As Comparator)
Dim i, pass As Integer
For pass = 0 To array.GetUpperBound(0)
For i = 0 To array.GetUpperBound(0) - 1
If Compare(array(i), array(i + 1)) Then
Swap(array(i), array(i + 1))
End If
Next
Next
End Sub
Private Sub Swap(ByRef firstElement As Integer, _
ByRef secondElement As Integer)
Dim hold As Integer
hold = firstElement
firstElement = secondElement
secondElement = hold
End Sub " Swap
End Class

</source>

==Two ways to init a Delegate==

<source lang="vbnet">
Imports System
Imports System.Collections

Delegate Sub DelegateWithStringSignature(ByVal S As String)
Delegate Sub DelegateWithNoParam()
public class MainClass
Shared Sub Main()
Dim c As New CalledClass()
Dim o As New OtherCalledClass()
Dim BadObject As New ObjectWithNoWriteMessage()
Dim d1 As DelegateWithStringSignature
Dim Params() As Object = {"DynamicParam"}
" The two following lines are identical
d1 = New DelegateWithStringSignature(AddressOf c.WriteMessage)
d1.Invoke("Test")
d1.DynamicInvoke(Params)
d1 = AddressOf c.WriteMessage
d1.Invoke("Test")
d1.DynamicInvoke(Params)
End Sub
End Class
Class CalledClass
Shared Sub SharedMessage(ByVal s As String)
Console.WriteLine("CalledClass.SharedMessage with parameter: " & s)
End Sub
Public Sub WriteMessage(ByVal s As String)
Console.WriteLine("CalledClass WriteMessage method with parameter: " & s)
End Sub
End Class
Class OtherCalledClass
Sub WriteMessage(ByVal s As String)
Console.WriteLine("OtherCalledClass WriteMessage method with parameter: " & s)
End Sub
End Class
Class ObjectWithNoWriteMessage
Sub BadWriteMessage()
End Sub
End Class

</source>

==Use Delegate to implement custome sort==

<source lang="vbnet">
Imports System
Public Class MainClass
Shared Sub Main( )
Dim Student1 As New Student("Student1")
Dim Student2 As New Student("Student2")
Dim Employee1 As New Employee(65)
Dim Employee2 As New Employee(12)
Dim studentPair As New Pair(Student1, Student2)
Dim employeePair As New Pair(Employee1, Employee2)
Console.WriteLine("studentPair: {0}", _
studentPair.ToString( ))
Console.WriteLine("employeePair: {0}", _
employeePair.ToString( ))
Dim theStudentDelegate As New _
Pair.WhichIsSmaller(AddressOf Student.WhichStudentIsSmaller)
Dim theEmployeeDelegate As New _
Pair.WhichIsSmaller(AddressOf Employee.WhichEmployeeIsSmaller)
studentPair.Sort(theStudentDelegate)
Console.WriteLine("After Sort studentPair: {0}", _
studentPair.ToString( ))
studentPair.ReverseSort(theStudentDelegate)
Console.WriteLine("After ReverseSort studentPair: {0}", _
studentPair.ToString( ))
employeePair.Sort(theEmployeeDelegate)
Console.WriteLine("After Sort employeePair: {0}", _
employeePair.ToString( ))
employeePair.ReverseSort(theEmployeeDelegate)
Console.WriteLine("After ReverseSort employeePair: {0}", _
employeePair.ToString( ))

End Sub "Main

End Class
Public Enum Comparison
theFirst = 1
theSecond = 2
End Enum
Public Class Pair
Private thePair(2) As Object
Public Delegate Function WhichIsSmaller(ByVal obj1 As Object, ByVal obj2 As Object) As Comparison
Public Sub New(ByVal firstObject As Object,ByVal secondObject As Object)
thePair(0) = firstObject
thePair(1) = secondObject
End Sub
Public Sub Sort(ByVal theDelegatedFunc As WhichIsSmaller)
If theDelegatedFunc(thePair(0), thePair(1)) = _
Comparison.theSecond Then
Dim temp As Object = thePair(0)
thePair(0) = thePair(1)
thePair(1) = temp
End If
End Sub
Public Sub ReverseSort(ByVal theDelegatedFunc As WhichIsSmaller)
If theDelegatedFunc(thePair(0), thePair(1)) = _
Comparison.theFirst Then
Dim temp As Object = thePair(0)
thePair(0) = thePair(1)
thePair(1) = temp
End If
End Sub
Public Overrides Function ToString( ) As String
Return thePair(0).ToString( ) & ", " & thePair(1).ToString( )
End Function
End Class
Public Class Employee
Private weight As Integer
Public Sub New(ByVal weight As Integer)
Me.weight = weight
End Sub
Public Shared Function WhichEmployeeIsSmaller(ByVal o1 As Object, ByVal o2 As Object) As Comparison
Dim d1 As Employee = DirectCast(o1, Employee)
Dim d2 As Employee = DirectCast(o2, Employee)
If d1.weight > d2.weight Then
Return Comparison.theSecond
Else
Return Comparison.theFirst
End If
End Function
Public Overrides Function ToString( ) As String
Return weight.ToString( )
End Function
End Class
Public Class Student
Private name As String
Public Sub New(ByVal name As String)
Me.name = name
End Sub
Public Shared Function WhichStudentIsSmaller( _
ByVal o1 As Object, ByVal o2 As Object) As Comparison
Dim s1 As Student = DirectCast(o1, Student)
Dim s2 As Student = DirectCast(o2, Student)
If String.rupare(s1.name, s2.name) < 0 Then
Return Comparison.theFirst
Else
Return Comparison.theSecond
End If
End Function
Public Overrides Function ToString( ) As String
Return name
End Function
End Class

</source>

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