How to delegate using ASP.NET 2.0 and VB.NET

This tutorial demonstrates how to sort employee of one company by the employee's salary asc with the Delegate technique and bubble sort.

This tutorial demonstrates how to sort employee of one company by the employee's salary asc with the Delegate technique and bubble sort. And this tutorial only using the default namespace.
A delegate is a type that references a method. Once a delegate is assigned a method, it behaves exactly like that method. The delegate method can be used like any other method, with parameters and a return value.

First, we need to Declares a delegate. And we use the btnSorter_Click event to do the work.

Public Delegate Function CompareOB(ByVal lhs As Object, ByVal rhs As Object) As Boolean

Protected Sub btnSorter_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btnSorter.Click

Dim employeelist As String = ""
Dim employees As Employee() = {New Employee(Me.lbljoy.Text.Trim(), Convert.ToDecimal(Me.lblsalaryjoy.Text.Trim())), New Employee(Me.lbljake.Text.Trim(), Convert.ToDecimal(Me.lblsalaryjake.Text.Trim())), New Employee(Me.lblpetter.Text.Trim(), Convert.ToDecimal(Me.lblsalarypetter.Text.Trim())), New Employee(Me.lblsam.Text.Trim(), Convert.ToDecimal(Me.lblsalarysam.Text.Trim()))}
Dim employeeCompareOB As New CompareOB(AddressOf Employee.isGreater)
BubbleSorter.Sort(employees, employeeCompareOB)
Dim i As Integer

For i = 0 To employees.Length - 1

employeelist += employees(i).ToString() + "<br>"

Next i

Me.lblResult.Text = employeelist.ToString()

End Sub

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The code of the Employee class as follows

Public Class Employee

Private name As String
Private salary As Decimal

Public Sub New(ByVal name As String, ByVal salary As Decimal)

Me.name = name
Me.salary = salary

End Sub

Public Overrides Function ToString() As String

Return String.Format(name + ":{0:C}", salary)

End Function

Public Shared Function isGreater(ByVal lhs As Object, ByVal rhs As Object) As Boolean

Dim employeelhs As Employee = CType(lhs, Employee)
Dim employeerhs As Employee = CType(rhs, Employee)
Return IIf(employeerhs.salary > employeelhs.salary, True, False)

End Function

End Class

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The code of the BubbleSorter class as follows

Public Class BubbleSorter

Public Shared Sub Sort(ByVal sortArry() As Object, ByVal gtMethod As CompareOB)

Dim i As Integer
For i = 0 To sortArry.Length - 1

Dim j As Integer
For j = i + 1 To sortArry.Length - 1

If gtMethod(sortArry(j), sortArry(i)) Then

Dim temp As Object = sortArry(i)
sortArry(i) = sortArry(j)
sortArry(j) = temp

End If

Next j

Next i

End Sub

End Class

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The front end BubbleSorterWithDelegateVB.aspx page looks something like this:

<table>

<tr>

<td style="width: 100px">name</td>
<td style="width: 100px">salary</td>

</tr>
<tr>

</tr>
<tr>

</tr>
<tr>

</tr>
<tr>

</tr>

</table>
 
<asp:Button ID="btnSorter" runat="server" Text="Sort" Width="78px" OnClick="btnSorter_Click" /><br />
<br />
<asp:Label ID="Label1" runat="server" Text="Display the sorted result:"></asp:Label>  <br />
<asp:Label ID="lblResult" runat="server" ForeColor="Red"></asp:Label>

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The flow for the code behind page is as follows.

Imports System
Imports System.Data
Imports System.Configuration
Imports System.Web
Imports System.Web.Security
Imports System.Web.UI
Imports System.Web.UI.WebControls
Imports System.Web.UI.WebControls.WebParts
Imports System.Web.UI.HtmlControls

Namespace BubbleSorter

Public Delegate Function CompareOB(ByVal lhs As Object, ByVal rhs As Object) As Boolean

Class _Default

Inherits System.Web.UI.Page
Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)

End Sub

Protected Sub btnSorter_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btnSorter.Click

employeelist += employees(i).ToString() + "<br>"

Next i
Me.lblResult.Text = employeelist.ToString()

End Sub

End Class

Public Class Employee

Private name As String
Private salary As Decimal

Public Sub New(ByVal name As String, ByVal salary As Decimal)

Me.name = name
Me.salary = salary

End Sub

Public Overrides Function ToString() As String

Return String.Format(name + ":{0:C}", salary)

End Function

Public Shared Function isGreater(ByVal lhs As Object, ByVal rhs As Object) As Boolean

Dim employeelhs As Employee = CType(lhs, Employee)
Dim employeerhs As Employee = CType(rhs, Employee)
Return IIf(employeerhs.salary > employeelhs.salary, True, False)

End Function

End Class

Public Class BubbleSorter

Public Shared Sub Sort(ByVal sortArry() As Object, ByVal gtMethod As CompareOB)

Dim i As Integer
For i = 0 To sortArry.Length - 1

Dim j As Integer
For j = i + 1 To sortArry.Length - 1

If gtMethod(sortArry(j), sortArry(i)) Then

Dim temp As Object = sortArry(i)
sortArry(i) = sortArry(j)
sortArry(j) = temp

End If

Next j

Next i

End Sub

End Class

End Namespace

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