asked on

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object. is the ERROR i get, why?

My class

Imports Microsoft.VisualBasic
Imports System.Web.UI

Public Class menu

Public Shared Sub Create_Side_Bars(ByVal x As Integer)

Dim Page As New Page
Dim myImage As Image = CType(Page.Master.FindControl("img_left_bar"), Image)
myImage.Height = x

End Sub

End Class

ERROR:

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

And highlights this line

Line 8: Dim myImage As Image = CType(Page.Master.FindControl("img_left_bar"), Image)

Can anyone help me?

samtran0331

try removing this line:
Dim Page As New Page

samtran0331

when you do this:
Dim myImage As Image = CType(Page.Master.FindControl("img_left_bar"), Image)

the "Page" is already defined as the current page you're working with

strickdd

It can't find the control called "img_left_bar". Either you are doing this too early in the page life cycle an need to wait until Page_PreRender, or the control "img_left_bar" is in a subcontrol of the Page.Master.

strickdd

For example if in the masterpage you have:

<asp:Panel id="something" runat="server">

<asp:image id="img_left_bar" ruant="server" imageurl="something.jpg"/>

</asp:Panel>

You might need to do this:

((Panel)Page.Master.FindControl("something")).FindControl("img_left_bar")

mmedi005

ASKER

I in the transition of going from asp to asp .net, would a Panel be the right way to go? I have thimage inside a div. Reason why is because the control I have with the CSS. Can I manipulate the position of a div with a panel.

I do keep getting errors where ever I place the Sub routine. Pre Render- Pre Load, etc...

Keeps referring that Page is Null.....

samtran0331

>>Keeps referring that Page is Null....
.
When you do this:

Dim Page As New Page
Dim myImage As Image = CType(Page.Master.FindControl("img_left_bar"), Image)

You:
1. Instantiate a page.
2. try to find the master page of the page you just instantiated.

the page exists, but only the instance in the first line...it doesn't actually exist as a real "something.aspx" page...that's why you're getting the error.

mmedi005

ASKER

But if I don't set it to new, visual studio complains about a possible runtime error if I just have

Dim myImage As Image = CType(Page.Master.FindControl("img_left_bar"), Image)
------

and it does error out....

so basically, i can not do this in a class, it would have to be in the actual webpage?

samtran0331

if you do it in a class, then you can pass the page to the class function...like...

class file:

Public Sub SetImage(byval ThePage as system.web.ui.page)
Dim myImage As Image = CType(ThePage.Master.FindControl("img_left_bar"), Image)
end sub

ASKER CERTIFIED SOLUTION

samtran0331

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samtran0331

also this:
http://aspnet.4guysfromrolla.com/articles/041305-1.aspx

between the 2 articles, you can piece together a way to use a base page class; which also works for master pages and you can create a base master page for code..and how to pass properties between a master/content pages