Nullreference exception - why?

Question

Panel pnl_Confirmation = (Panel)form1.FindControl("ConfirmationPanel") as Panel;
    pnl_Confirmation.Visible = false;

I keep getting a "NullReferenceException" in the above code. "ConfirmationPanel" is a panel I show/hide depending on if the form is submitted successfully or not.

The panel is wrapped in a LoginView control, which is why I cannot call "ConfirmationPanel" directly:

<asp:LoginView ID="LoginView1" runat="server">
<LoggedInTemplate> 
<asp:Panel id="ConfirmationPanel" runat="server" Wrap="False">

...

Why is this null? It should be referencing the Panel with the ID "ConfirmationPanel", no?

Thanks

Panel pnl_Confirmation = (Panel)form1.FindControl("ConfirmationPanel") as Panel; Why are you casting twice? — Gabe
– Gabe, Commented Nov 19, 2010 at 21:18
This may not be the sort of comment you want, but is there any way you can work with MVC instead? ASP.NET webforms is concentrated evil. — Juliet
– Juliet, Commented Nov 19, 2010 at 21:19
You don't need both types of type casts: "as Panel" is sufficient. — TreDubZedd
– TreDubZedd, Commented Nov 19, 2010 at 21:20
is the panel visible for the first time when you execute the statement Panel pnl_Confirmation = (Panel)form1.FindControl("ConfirmationPanel") as Panel; ? — genericuser
– genericuser, Commented Nov 19, 2010 at 21:20

Gabe · Accepted Answer · 2010-11-19 21:20:23Z

4

Try this:

Panel pnl_Confirmation = LoginView1.FindControl("ConfirmationPanel") as Panel;
if(pnl_Confirmation != null)
   pnl_Confirmation.Visible = false;

answered Nov 19, 2010 at 21:20

Gabe

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1 Comment

Kolten Over a year ago

This worked. Thanks! It seems I was casting twice, as well as referencing from "form1" instead of "LoginView1".

Otávio Décio · Accepted Answer · 2010-11-19 21:19:51Z

2

It all depends where you have that code. If you have it before Page_Load(), the control tree is probably not built yet, hence the null reference.

answered Nov 19, 2010 at 21:19

Otávio Décio

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Comments

Marko · Accepted Answer · 2010-11-19 21:20:59Z

1

Use the FindControl of LoginView instead

Panel pnl_Confirmation = LoginView1.FindControl("ConfirmationPanel") as Panel;

Because it's part of the LoginView template.

answered Nov 19, 2010 at 21:20

Marko

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Comments

Mister Cook · Accepted Answer · 2010-11-19 21:24:36Z

1

"FindControl will find a control only if the control is directly contained by the specified container; that is, the method does not search throughout a hierarchy of controls within controls. " (from the MSDN documentation)

i.e. call FindControl on LoginView or create a recursive FindControl

answered Nov 19, 2010 at 21:24

Mister Cook

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Comments

Will Marcouiller · Accepted Answer · 2010-11-19 21:20:23Z

0

It seems you try to typecast twice.

Try to only typecast once with either works best:

Panel pnl_Confirmation = (Panel)form1.FindControl("ConfirmationPanel");

or

Panel pnl_Confirmation = form1.FindControl("ConfirmationPanel") as Panel;

It is also important to verify whether your reference is not null before trying to access it

if (pnl_Confirmation != null)
    pnl_Confirmation.Visible = false;

answered Nov 19, 2010 at 21:20

Will Marcouiller

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