Losing selectedIndex on Control inherted from ListBox during postback

22 Apr 2005 1:24 PM

chambersdon

I have created a Web Custom Control that inherits from
WebControls.ListBox but can't get it to retain the selectedIndex after
a postback. As a test I created a very simple version of the control
with no additional code. I just inherited from the exisiting ListBox
class and put the control on a page.

I put this control a blank page along with a button to perform a post
back. I select an item in the list box and then click the button and
after the postback I have lost the selected value. I added some
javascript to alert to the selectedIndex just to make sure the client
had one and it did.

EnableViewState is set to true for this control. If I make a custom
textbox in the same method it's value is retained after postback with
no additional code. If I put a standard ListBox on the page it's
selectedIndex is retained after postback with no additional code.

Thanks,
Don

22 Apr 2005 4:49 PM

Jorge L Matos

Make sure you're not populating the listbox in the page_load event for every
page request. You need to make sure you check the "IsPostBack" property
before populating the control. If you forget then the selected value will
not be shown in the listbox because you're initialized it again.

void Page_Load()
{
      if (!IsPostBack)
      {
           //Initialize/DataBind List Box
      }
}

If that doesn't work, try posting some of your code to the newsgroup.

HTH,
Jorge

Show quoteHide quote

"chambers***@hotmail.com" wrote:

> I have created a Web Custom Control that inherits from
> WebControls.ListBox but can't get it to retain the selectedIndex after
> a postback. As a test I created a very simple version of the control
> with no additional code. I just inherited from the exisiting ListBox
> class and put the control on a page.
>
>
> I put this control a blank page along with a button to perform a post
> back. I select an item in the list box and then click the button and
> after the postback I have lost the selected value. I added some
> javascript to alert to the selectedIndex just to make sure the client
> had one and it did.
>
>
> EnableViewState is set to true for this control. If I make a custom
> textbox in the same method it's value is retained after postback with
> no additional code. If I put a standard ListBox on the page it's
> selectedIndex is retained after postback with no additional code.
>
>
> Thanks,
> Don
>
>