FindControl not working in content page

Question

User1900948409 posted
i have the following:
<asp:Content ContentPlaceHolderID="plcMainContent" ID="cntMain" runat="server">
    ...
    <asp:Panel id="pnlThumb1" runat="server" Visible="true"/>
    ...
</asp:Content>

if i call this:
    this.pnlThumb1.Visible = false;
no problems.

but if i call this:
    this.FindControl("pnlThumb1").Visible = false;

i get a NullReferenceException telling me it can't find it.

i thought maybe it was because it's in a content place holder (FindControl only works on the top level control), but there's not way to reference the "cntMain." so i can't do cntMain.FindControl.

any ideas?

Answer 1

User1900948409 posted
ok, i figured this out. it's really a cr**py implementation in my opion by the ASP.NET team, but this is what you have to do.

1) in your content page, add the following:
<%@ MasterType TypeName="MasterDefault" %>

where "MasterDefault" is the class name of your master file.

you don't actually have to do this, but if you don't, when you reference this.Master on the page you're working on, it'll actually give you the MasterPage class, rather than your own masterpage type. ok, weird. by adding this you save yourself a few lines of code in the page.

2) get a reference to your content place holder:
ContentPlaceHolder mainContent = (ContentPlaceHolder)this.Master.FindControl("plcMainContent");

NOTE: when you do find control, you need to put in the ContentPlaceHolderID NOT the ID of the ContentPlace holder. backwards enough for you? as an example, this is my <asp:Content> tag:
<asp:Content ContentPlaceHolderID="plcMainContent" ID="cntMain" runat="server">

3) once you have the refernce to that content holder, run FindControl as you normally would:
mainContent.FindControl("pnlThumb1").Visible = false;

so in conclusion, you:

add:
    <%@ MasterType TypeName="MasterDefault" %>
to your .aspx content page
and do this in your code:ContentPlaceHolder mainContent =         (ContentPlaceHolder)this.Master.FindControl("plcMainContent");
    mainContent.FindControl("pnlThumb1").Visible = false;

Answer 2

User686179636 posted

Thanks for sharing !!! 

Answer 3

User-1107059751 posted

This was very helpful review.  Thanks for sharing it with us. 

 

Nirmala

Answer 4

User43235592 posted

Thanks..dear it poped me out from a stuck.

 its really helpful

 Balpreet Patil ([e-mail])
 

Answer 5

User2013597856 posted

Good reply, it's probably a good idea to note that this is due to the late binding approach that you are using; however, you could also early bind this object/control as well:

pnlThumb1.Visible = false;

k

Answer 6

User-919465860 posted

Thanks a lot dear friend. 

Answer 7

User315369078 posted

Thank you! 

Answer 8

User-212733016 posted

You could create a more elegant solution by using a bit of reflection combined with extension classes:

public static class PageExtensions
{
        public static T GetControl<T>(this Page page, string name) where T : Control
        {
            FieldInfo field = page.GetType().GetField(name, System.Reflection.BindingFlags.IgnoreCase | System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.NonPublic);
            if (field != null)
                return (T)field.GetValue(page);
 
            return null;
        }
}

 

The call would then be

this.GetControl<Panel>("pnlThumb1").Visible = false;

Please find the complete sample with description on my blog

http://www.iucon.biz/blog/index.php/2008/10/10/solution-for-findcontrol-with-masterpages/

Answer 9

User-1527108608 posted

thanks so much

Answer 10

User1014984822 posted

Thank you so much for this answer.  It got my FindControl working !!! 

Answer 11

User-2118676656 posted

Another very succint, simple solution may be foud here:

http://forums.asp.net/p/1564614/3953981.aspx#3953981 

Answer 12

User-532303751 posted

Wow.  Thanks so much.

I'm dynamically creating controls in the Page Init event of a content page and was very surprised to find that I could not reference the controls I created.  This will save me a LOT of time.