In general when we load a User control with the Page.LoadControl() method, the
User control is returned as an instance of the System.Web.UI.Control class. This
means that if the User control includes any custom properties, the properties
aren't available when we dynamically load the User control. If we dynamically
load a User control, then we need to cast the control to the correct type before
we can access any of the control's custom properties. To get a reference to a
User control's type, we must use the <%@ Reference %> directive.
Taking an example, imagine that we need to create a form that displays different
questions depending on the answers that a user provides for previous questions.
In that case, we can dynamically load different User controls that contain the
different sets of questions. The page given below contains a survey form. The
first question asks us whether we are currently using VS 4.0 or VS 3.5 and
depending on our answer, the remainder of the form displays different questions.
Default2.aspx File Code
<%@
Page Language="VB"
%>
<%@
Reference Control="~/ASPSurvey.ascx"
%>
<%@
Reference Control="~/ASPNetSurvey.ascx"
%>
<!DOCTYPE
html PUBLIC
"-//W3C//DTD XHTML 1.1//EN"
"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<script
runat="server">
Private
_survey As
Control =
Nothing
Private
Sub Page_Load()
Select Case
ddlLanguage.SelectedIndex
Case 1
_survey = Page.LoadControl("ASPSurvey.ascx")
Case 2
_survey = Page.LoadControl("ASPNetSurvey.ascx")
End Select
If
Not IsNothing(_survey)
Then
PlaceHolder1.Controls.Add(_survey)
End If
End Sub
Protected
Sub btnSubmit_Click(ByVal
sender As Object,
ByVal e As
EventArgs)
Select Case
ddlLanguage.SelectedIndex
Case 1
Dim aspResults
As
ASPSurvey = CType(_survey,
ASPSurvey)
ltlResults.Text =
"<h1>ASP Survey</h1>"
ltlResults.Text +=
"<br/>ASP is fast? " + aspResults.KnowFast.ToString()
ltlResults.Text += "<br
/>ASP is very difficult to learn? " + aspResults.KnowNewest.ToString()
Case 2
Dim aspNetResults
As
ASPNetSurvey = CType(_survey,
ASPNetSurvey)
ltlResults.Text =
"<h1>PHP Survey</h1>"
ltlResults.Text +=
"<br />PHP is fast? " + aspNetResults.KnowSlow.ToString()
ltlResults.Text += "<br
/>PHP is very difficult to learn? " +
aspNetResults.KnowOutdated.ToString()
End Select
End Sub
</script>
<html
xmlns="http://www.w3.org/1999/xhtml"
>
<head
id="Head1"
runat="server">
<style
type="text/css">
html
{
font:14px
Arial,Sans-Serif;
background-color:Aqua;
}
</style>
<title>Web
Survey</title>
</head>
<body>
<form
id="form1"
runat="server">
<div>
<asp:Label
id="lblLanguage"
Text="What
language do you use to develop Web applications?"
Runat="server"
/>
<br
/>
<asp:DropDownList
id="ddlLanguage"
ToolTip="Web
application language (reloads form)"
AutoPostBack="true"
Runat="server">
<asp:ListItem
Text="Select
Language" />
<asp:ListItem
Text="ASP"
/>
<asp:ListItem
Text="PHP"
/>
</asp:DropDownList>
<br
/><br
/>
<asp:PlaceHolder
id="PlaceHolder1"
Runat="server"
/>
<asp:Button
id="btnSubmit"
Text="Submit"
OnClick="btnSubmit_Click"
Runat="server"
/>
<hr
/>
<asp:Literal
id="ltlResults"
Runat="server"
/>
</div>
</form>
</body>
</html>
Now depending on the user's selection from the DropDownList control, one of two
User controls is loaded in the Page_Load() event handler: the ASPSurvey.ascx or
the PHPSurvey.ascx User control. When we submit the survey form, the
btnSubmit_Click() method executes. This method casts the User control loaded in
the form to the correct type. It casts the User control to either the ASPSurvey
or the PHPSurvey type.
ASP.Survey.ascx File Code
<%@
Control Language="VB"
ClassName="ASPSurvey"
%>
<script
runat="server">
Public ReadOnly
Property KnowFast()
As Boolean
Get
Return chkFast.Checked
End Get
End
Property
Public ReadOnly
Property KnowNewest()
As Boolean
Get
Return chkNewest.Checked
End Get
End
Property
</script>
<asp:CheckBox
id="chkFast"
Text="Did
you know that ASP is fast?"
Runat="server"
/>
<br
/><br
/>
<asp:CheckBox
id="chkNewest"
Text="Did
you know that ASP is very difficult to learn?"
Runat="server"
/>
<br
/><br
/><br
/>
PHPSurvey.ascx File Code
<%@
Control Language="VB"
ClassName="PHPSurvey"
%>
<script
runat="server">
Public ReadOnly
Property KnowSlow()
As Boolean
Get
Return chkSlow.Checked
End Get
End
Property
Public
ReadOnly Property
KnowOutdated() As
Boolean
Get
Return chkOutdated.Checked
End Get
End
Property
</script>
<asp:CheckBox
id="chkSlow"
Text="Did
you know that PHP is slow?"
Runat="server"
/>
<br
/><br
/>
<asp:CheckBox
id="chkOutdated"
Text="Did
you know that PHP is very difficult to learn?"
Runat="server"
/>
<br
/><br
/><br
/>
It is very easy to develop and widely used over web.
HAVE A GREAT CODING!