In our new ASP.Net app, we are using one list box that allows multiple-select. Recently, choosing one of the items in the list produced no results. But items would not be in the list if there were no results, so there must be a problem in the SQL statement related to the multiple-select list or the data. In classic ASP, you would access the multiple items like this:
where i is the form item and j is the result of the multiple-select. Unfortunately, that does not work in ASP.Net. If you access the form item directly in ASP.Net, like this:
it provides a comma-delimited list of the multiple form items. It’s pretty easy to then split the list on the commas, and that was what we were doing. Ahh, the bad item in the list had a comma embedded in its text. So it was splitting inappropriately and creating a bad SQL statement for fetching results. This was the source of the problem here. There must be a way to access the items individually, but it was not obvious to me. I must have stared at the MSDN docs forever trying to find the answer. I had to try three or four different keyword searches on Google before I found an excellent explanation here.
The results of a mulitple-select list are also a NameValueCollection, just like the Request.Form. Once I found that, it was easy to get at the individual items. The entire collection is accessed like this:
and the individual items are accessed like this:
I was really surprised at how difficult it was to find this information. Both of my favorite ASP.Net books, Essential ASP.Net by Fritz Onion and Programming ASP.Net by Dino Esposito both had no mention of the embedded NameValueCollection. This seems like it would be a common problem for developers using forms, but I did not find the answer to be as obvious.