I am trying to get a handle on how to set and access properties of a
UserControl from a WebForm that consumes the UserControl. From what I can
tell by looking at past posts and from talking with others, there is a lot
of interest in this area but few answers.
I've been experimenting tonite and am hoping by starting this thread I can
stimulate some good discussion on this topic. To start off, I've created a
simple WebForm and UserControl. All I want to do at this point is to set a
Property in the UserControl from the WebForm's Page Load event. Seems simple
enough, but I cannot figure out how to keep the UserControl from showing up
twice on the rendered page. And it raises some questions about the way .NET
compiles and renders a WebForm.
Here's the key blocks of code, and then some questions/observations follow:
=========== WEBFORM CODEBEHIND ==============
Protected Sub WebForm1_Load(ByVal Sender As System.Object, ByVal e As
System.EventArgs)
Trace.Write("webform1", "Entering webform1_Load")
Response.Write("This page will tell you my name...maybe:<br><p>")
If Not IsPostback Then ' Evals true first time browser hits the
page
Dim myControl As Control = Page.LoadControl("usercontrol1.ascx")
Dim myUC As usercontrol1 = CType(myControl, usercontrol1)
myUC.Name = "Patrick"
Page.Controls.Add(myControl)
End If
Trace.Write("webform1", "Exiting webform1_Load")
End Sub
=========== WEBFORM ===========
<%@ Page Language="vb" AutoEventWireup="false" Codebehind="WebForm1.vb"
Inherits="test.WebForm1"%>
<%@ Register TagPrefix="UC" TagName="myUCs" src="usercontrol1.ascx" %>
<html>
<head>
<meta name="GENERATOR" content="Microsoft Visual Studio.NET 7.0">
<meta name="CODE_LANGUAGE" content="Visual Basic 7.0">
</head>
<body>
<form id="WebForm1" method="post" runat="server">
Text Before the UserControl<br><p>
<UC:myUCs id="myUC1" runat="Server" />
Text After the UserControl
</form>
</body>
</html>
=========== USERCONTROL CODEBEHIND ===========
Private _name As String
Public Property Name() As String
Get
Return _name
End Get
Set
_name = value
End Set
End Property
Protected Sub usercontrol1_Load(ByVal Sender As System.Object, ByVal e
As System.EventArgs)
Trace.Write("usercontrol1", "Entering usercontrol1_Load with Name
property = " & Name)
If Not IsPostback Then ' Evals true first time browser hits the
page
Response.Write("Ah, yes! My name is " & Name & "<br><p>")
End If
Trace.Write("webform1", "Exiting usercontrol1_Load")
End Sub
=========== HOW THE PAGE RENDERS: ===========
This page will tell you my name...maybe:
Ah, yes! My name is
Ah, yes! My name is Patrick
Text Before the UserControl
This is some text from the usercontrol
Text After the UserControl
This is some text from the usercontrol
=========== QUESTIONS / OBSERVATIONS ===========
1. I tried a number of ways to set the Name property from the WebForm's
codebehind. The one that, at least from the VS.NET IntelliSense seemed like
it would work, was to declare an instance of the UserControl's codebehind
class (usercontrol1) and then simply set a Public variable strName (at the
time, not even a Property) on the codebehind:
e.g., Dim myUserControl As usercontrol1
myUserControl.strName
I got no compile errors with this syntax, but I would get a runtime
"Attempting to dereference a null object reference" error. Adding the
Trace.Write statements made me realize that the page leaves the Load event
prior to loading any UserControls. So there was no usercontrol1 class
instantiated on the server at the time I tried to set strName (I think I'm
right on that).
Does anyone have any comments on this? Am I on the right track? Does this
mean that the only (or best?) way to set a UserControl variable/property
value if it is needed in the UserControl's Load event is to use
Page.LoadControl and Page.Controls.Add?
2. If my conclusions from #1 are correct, how do I avoid having the page
load and display the UserControl twice? I tried removing the @Register
directive but then it threw a predictable error that it couldn't identify
the tagprefix and tagname I was using to consume the UserControl in the
WebForm. So I tried removing <UC:myUCs id="myUC1" runat="Server" />
altogether but then this resulted in the text from the UserControl ("This is
some text from the usercontrol") displaying *prior* to the text from the
WebForm ("Text Before the UserControl"). Thus, how do I load a UserControl
from my WebForm's Load event and set properties AND have the usercontrol
show up in the right spot on the rendered page, and only when I want it to
(i.e., not twice).
3. This is a related question: What would the syntax be for accessing a
property of the WebForm called, for example, "Address" from the UserControl?
(E.g,: something like Parent.Page.Address?) What would be the syntax for
accessing the "Address" property of a UserControl whose ID is, for example,
"UC3" from another UserControl consumed by the same WebForm? (E.g.,
something like Parent.Page.Controls.FindControl("UC3").Address?
=======================
I hope this stimulates some good discussion on these matters. Of course, an
authoritative voice chiming in with comments and definitive answers would
also be nice ; - ).
Thanks to all who have read this far,
Patrick
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