how to access PlaceHolder from codeBehind (class - .dll file) ???? PLEASE HELP

gonzal kamikadze · Oct 3, 2005

Hi

It is possible to access a placeHolder in a aspx page from a class (compiled
code)?
(coding in VB)

--- ASPX page ---
<%@ Page Language="VB" ContentType="text/html" ResponseEncoding="iso-8859-1"
debug="true" %>
<%@ Import Namespace="myNameSpace" %>
<script runat="server">
Sub page_Load()
Dim myClass As New testClass
myClass.testSub
End Sub
</script>
<html>
<title>test page</title>
<body>
<form ID="form1" runat="server">
<asp

laceHolder ID="plhTest" runat=server" />
</form>
</body>
</html>

--- page.vb ---
Imports system
Imports System.Web.UI
Imports System.Web.UI.WebControls
Imports System.Web.UI.HtmlControls

Namespace myNameSpace
Public Class testClass
Inherits Page
Public plhTest as PlaceHolder

Sub testSub()
Dim myLabel As New Label
myLabel.Text = " - TEST LABEL - "
plhTest.Controls.Add(myLabel)
End Sub
End Class
End Namespace

I'm getting all the time an error message like this:
System.NullReferenceException: Object reference not set to an instance of an
object.

does anybody know the solution to the above problem??? thanks

regards

nikki · Oct 3, 2005

Sure it's possible. You are declaring it, but I don't see FindControl
or a check that it exists anywhere...
You need to do FindControl.

Relevant snippets from my C# app...
Control placeholder = this.FindControl("legacyPlaceholder");
....
placeholder.Controls.Add(h);

clintonG · Oct 5, 2005

FindControl is late bound and imposes performance penalties.
An early bound approach would use a public property.

That allows the objects to be initialized by the Page class at runtime which
makes it easy for us to simply refer to merhods or properties using dotted
grammar from Page_Load or wherever.

I'm just about mastering this myself and only use FindControl at design-time
and then try to refactor the code manually. Next on the learning curve is to
learn how to use Visual Studio to refactor the code which is a feature I'm
fairly certain Visual Studio supports. At least for C#.

<%= Clinton Gallagher
METROmilwaukee (sm) "A Regional Information Service"
NET csgallagher AT metromilwaukee.com
URL http://metromilwaukee.com/
URL http://clintongallagher.metromilwaukee.com/

Patrice · Oct 5, 2005

For now my guess is that the variable is not considered as being a match for
the control markup (try perhaps "protected" instead of "public").

nikki · Oct 5, 2005

clintonG said:
FindControl is late bound and imposes performance penalties.

Really?
What kind?
Under what situations is it a bad thing to use?
Any articles you could point me to?

Thx.

clintonG · Oct 5, 2005

To start getting insight into this topic...
google: late bound vs early bound asp.net performance

There's much I need to learn myself.

<%= Clinton Gallagher
METROmilwaukee (sm) "A Regional Information Service"
NET csgallagher AT metromilwaukee.com
URL http://metromilwaukee.com/
URL http://clintongallagher.metromilwaukee.com/

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how to access PlaceHolder from codeBehind (class - .dll file) ???? PLEASE HELP

gonzal kamikadze

nikki

clintonG

Patrice

nikki

clintonG

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