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What's the problem with Page_Load?

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This message was discovered on ASPFriends.com 'aspngreuse' list.

Jon Maz

-- Moved from [aspngfreeforall] to [aspngreuse] by Marcie Jones <Click here to reveal e-mail address> --

Hi,

I have a simple UserControl that queries a DB and displays the query result
in a DropDownList. The page holding the UserControl should have access to
the value of the selected item in this DropDownList via a Public Property of
the UserControl called "PostedBy" (all code below).

The code seems to work fine if I access the .PostedBy property of the
UserControl in an "onclick" event handler subroutine. But if I try to
access this property (using the same code!) in Page_Load I get the following
error:

Object reference not set to an instance of an object.

My code seems fine to me, I can't work it out! Hope someone can tell me
what's going on!

Thanks in advance,

JON

*****************************************
MAINPAGE.aspx - displays the User Control
*****************************************

<%@ Page Language="VB" %>
<%@ Import Namespace="System.Data" %>
<%@ Import Namespace="System.Data.Oledb" %>

<%@ Register TagPrefix="PostedByDDL" TagName="UserControl"
src="POSTEDBY.ascx" %>

<script language="VB" runat="server">

Sub Page_Load(obj as object, e as EventArgs)

'***********************************
'* THIS DOES NOT WORK IN PAGE_LOAD
'***********************************
Dim iExampleInteger as Integer = ucPostedByDDL.PostedBy
Response.Write("iExampleInteger is :" & iExampleInteger)

If not Page.IsPostBack
DataBind()
end if

end sub

Sub Cheese(obj as object, e as eventargs)
'****************************************
'* BUT IT WORKS FINE IN THIS SUBROUTINE
'****************************************
Dim iExampleInteger as Integer = ucPostedByDDL.PostedBy
Response.Write("iExampleInteger is :" & iExampleInteger)
End sub

</script>

<html>
<form runat="server">

PostedBy: <PostedByDDL:UserControl id="ucPostedByDDL" runat="server"
/>
<br>
<asp:LinkButton runat="server" OnClick="Cheese" Text="Cheese" />

</form>
</html>

*****************************************
POSTEDBY.ascx - a simple User Control
*****************************************

<%@ Control Language="VB" %>
<%@ Import Namespace="System.Data" %>
<%@ Import Namespace="System.Data.Oledb" %>

<script language="VB" runat="server">

Dim objDatabase as new BusinessObjects.Database
Dim ds as new DataSet()

Sub Page_Load(obj as object, e as eventargs)

objDatabase.ConnectionString =
ConfigurationSettings.AppSettings("ConnectionString")
objDatabase.DataSet = ds

objDatabase.CreateDataTable("tblPostedBy", "SELECT * FROM
tblPeople;")
ddPostedBy.DataSource = ds.Tables("tblPostedBy")
ddPostedBy.DataTextField = "People"
ddPostedBy.DataValueField = "PersonID"

If not Page.IsPostBack then
ddPostedBy.DataBind()
ddPostedBy.Items.FindByText("Smith, Mike").Selected = true
end if

end sub

Public Property PostedBy As Integer
Get
Return ddPostedBy.SelectedItem.Value
End Get
Set
ddPostedBy.SelectedItem.Selected = false
ddPostedBy.Items.FindByValue(value).Selected = true
End Set
End Property

</script>

<asp:DropDownList runat="server" id="ddPostedBy" />

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Reply to this message...

Jon Maz

Hi All,

I have the answer, but don't know why it works! In MAINPAGE.aspx, if I put
the code:

Dim iExampleInteger as Integer = ucPostedByDDL.PostedBy
Response.Write("iExampleInteger is :" & iExampleInteger)

in Page_PreRender instead of Page_Load, it works as planned. Putting it in
Page_Init, which I also tried, does NOT work.

Does anybody out there have an explanation for this?

JON

PS Thanks to Marcie Jones, whose idea this actually was!

---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.361 / Virus Database: 199 - Release Date: 07/05/2002

Reply to this message...

Chris Kinsman

I suspect the issue is that in Page_Init the user control hasn't had a
chance to load it's information out of ViewState or out of the postback
data. Depending on how the control loads it's information Page_Load
could also be to early. I think however this last one is dependent upon
the implementation of the user control.

-----Original Message-----
From: Jon Maz [mailto:Click here to reveal e-mail address]=20
Sent: Monday, May 13, 2002 2:08 PM
To: aspngreuse
Subject: [aspngreuse] Re: What's the problem with Page_Load?

Hi All,

I have the answer, but don't know why it works! In MAINPAGE.aspx, if I
put
the code:

Dim iExampleInteger as Integer =3D ucPostedByDDL.PostedBy
Response.Write("iExampleInteger is :" & iExampleInteger)

in Page_PreRender instead of Page_Load, it works as planned. Putting it
in
Page_Init, which I also tried, does NOT work.

Does anybody out there have an explanation for this?

JON

PS Thanks to Marcie Jones, whose idea this actually was!

---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.361 / Virus Database: 199 - Release Date: 07/05/2002

| [aspngreuse] member Click here to reveal e-mail address =3D YOUR ID
| http://www.aspfriends.com/aspfriends/aspngreuse.asp =3D JOIN/QUIT

Reply to this message...

	System.Configuration.ConfigurationSettings
	System.Data.DataSet
	System.EventArgs
	System.Web.UI.Page
	System.Web.UI.UserControl
	System.Web.UI.WebControls.DropDownList
	System.Web.UI.WebControls.LinkButton
	System.Windows.Forms.UserControl

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