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This example shows you how to create a simple and original data-bound custom server
control—a data-bound bulleted list.The CustomBulletedList class is as follows:
Imports System
Imports System.Web.UI
Imports System.Web.UI.WebControls
Imports System.ComponentModel
Imports System.Collections
Imports System.Text
Public Class CustomBulletedList
Inherits System.Web.UI.WebControls.WebControl
Private _html As New StringBuilder()
Private _dataSource As IEnumerable
Public Property DataSource() As IEnumerable
Get
Return _dataSource
End Get
Set(ByVal value As IEnumerable)
_dataSource = value
End Set
End Property
Private Sub CreateBulletedList()
Dim dataSource As IEnumerable = Nothing
Try
dataSource = Me._dataSource
Catch
End Try
If Not (dataSource Is Nothing) Then
_html.Append(“<ul>”)
Dim dataObject As Object
For Each dataObject In dataSource
_html.Append(“<li>”)
_html.Append(dataObject)
_html.Append(“</li>”)
Next dataObject
_html.Append(“</ul>”)
End If
End Sub
Public Overrides Sub DataBind()
MyBase.OnDataBinding(EventArgs.Empty)
CreateBulletedList()
End Sub
Protected Overrides Sub Render(ByVal output As HtmlTextWriter)
output.Write(_html)
End Sub
End Class
To use this control, you need to do the following:
<%@ Page Language=”VB” %>
<%@ Register TagPrefix=”AspNet” Namespace=”AspNet”
Assembly=”AspNet” %>
<!DOCTYPE HTML PUBLIC “-//W3C//DTD HTML 4.0 Transitional//EN” >
<html>
<head>
<title>Data Bound Controls</title>
</head>
<body>
<script language=”vb” runat=”server”>
Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs)
listControl.DataSource = New String() {“Test 1”, “Test 2”, “Test 3”}
listControl.DataBind()
End Sub
</script>
<AspNet:CustomBulletedList id=”listControl” runat=”server”/>
</body>
</html>
This control allows you to data-bind any data source that is derived from IEnumerable
to it—the content will be listed in bulleted format. Overriding the DataBind method is
the critical point in this control.When this method is called, it is trying to bind to the
data source and call the CreateBulletedList method.
CreateBulletedList loops through all of the data objects in the data source and
saves them to be outputted as bulleted lines.
By overriding the Render method, you can control the rendering of the control, and
render it exactly as you see fit.You should always opt for this approach when performance
is an issue (and when isn’t it?), because it is much faster than overriding the
CreateChildControls method.
One last point you should take note of is that you should always use a StringBuilder
instead of a regular string as the HTML output source. Using regular string objects will
seriously degrade the performance of your custom control.
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