Delegates in Visual Basic.NET

Delegates are objects that can call the methods of other objects for you. For this reason, delegates

 are sometimes described as type-safe function pointers. Visual Basic.NET has moved to an event model that 

is based on delegates. Although you can create your own delegates, in most cases Visual Basic.Net will 

create the delegate and take care of the details for you. But in certain case you have to create them. Here is 

a sample that demonstrate the creation and use of Delgates with Visual Basic.NET. To get it to run in Visual 

Studio.NET, create a new console application and paste the code below into Module1.vb.

 

'Applicatio : Console

'History   :

Module Module1

    'Define a Delegate

    Delegate Sub CompareFunc(ByVal x As Integer, _

      ByVal y As Integer, ByRef b As Boolean)

    'Define a Event that will be used in AddHandler

    Public Event a As CompareFunc

    'Bubble Sort Algorithm which calles Delegates to perform work

    Function BubbleSort(ByVal SortHigher As CompareFunc, _

        ByVal IntArray() As Integer) As Integer()

        Dim I, J, Value, Temp As Integer

        Dim b As Boolean

        For I = 0 To Ubound(IntArray)

            Value = IntArray(I)

            For J = I + 1 To UBound(IntArray)

                Try

                    SortHigher.Invoke(IntArray(J), Value, b)

                    If b = True Then

                        Temp = IntArray(J)

                        IntArray(J) = Value

                        IntArray(I) = Temp

                        Value = Temp

                    End If

                Catch

                    'Add error handling here, or just proceed

                End Try

            Next J

        Next I

    End Function

    'Actual Event handling , called by Delgates

    Sub Fire(ByVal x As Integer, ByVal y As Integer, ByRef b As Boolean)

        If y > x Then

            b = True

        Else

            b = False

        End If

    End Sub

    'Entry point

    Sub Main()

        Dim IntArray() As Integer = {12, 1, 96, 56, 70}

        Dim iArrayCount As Integer

        Dim iCounter As Integer

        ' Add a delegate Handler

        AddHandler a, (AddressOf Fire)

        'Define Array for Sorting

        iArrayCount = IntArray.Length

        Console.WriteLine("Integer array to be sorted")

        For iCounter = 0 To iArrayCount - 1

            Console.WriteLine(" Value at{0} is {1} ", _

                 iCounter, IntArray(iCounter))

        Next

        'Call the method which is going to raise events

        BubbleSort(Module1.aEvent, IntArray)

        iArrayCount = IntArray.Length

        Console.WriteLine("Integer array after Bubble Sort with Delegate")

        'Display the Data to user on Console

        For iCounter = 0 To iArrayCount - 1

            Console.WriteLine(" Value at{0} is {1}", _

              iCounter, IntArray(iCounter))

        Next

    End Sub

End Module