Listbox only posts data for selected items

[Guest]

Hi,
I have a listbox (in a user control) which has items add/removed via
javascript (i.e. an "add item" link which uses a popup selection screen to
add items and a "remove item" link which deletes any selected row(s)).

There is a strange problem that when I inspect the list of items during a
postback the list appears to be empty (even though I added items). I noticed
that when I multiselect one or more items, only those selected items are
posted back!

What the heck is going on?! I'm not doing any other processing that may be
related to this problem.

Thanks

 

[Walter Wang [MSFT]]

Hi,

It's because using client-side code, the ViewState cannot be modified, so
when the ListBox is rebuilt on postback, it won't have the information in
the ViewState about the new items.

A workaround is: when adding the items client-side, also save the info to a
hidden input field. In Page_Load, get the information from the hidden input
field and add the items. This will put it into the ViewState.

For a complete working sample, you can refer to following URL:

http://metabuilders.com/Tools/DynamicListBox.aspx

It contains a ASP.NET 1.1 custom control DynamicListBox which can add items
at client-side using javascript and still retain them on postback.

I hope this helps. Please feel free to post here if anything is unclear.

Sincerely,
Walter Wang ([email protected], remove 'online.')
Microsoft Online Community Support

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