As Infragistics webcombo (current latest is v7.3) doesn't directly support multiple selection yet as mentioned here I figured I'd post a work around I did while facing the same issue.
Attaching a sample ASP.NET Website Project to this post (see below) but basically it involves a checkbox column within the webcombo. [more]
However, encountered a few issues in firefox and thus more work-around:
1. clicking on the checkbox column closes up the dropdown – override aftercloseup and afterdropdown client side events to prevent the close up unless the mouse is clicked outside of the dropdown
2. even with the on postback/callback – before posting back (or callback) to the server, saved the selected values (IDs where checkbox was checked) in a hidden form (vertical tab delimited) and parse in the server side.
This was a little pain for something that seems to be a simple requirement so would appreciate any comments or if there is a much simpler solution.
Hope this helps anyone.
And just a little after I posted this I came across this which pretty much does the same thing as above only better 🙂 Turn WebCombo into multiselect Checkbox Combo
This means i'll have to revisit my solution above. Good find.