Hello Stewart,

Please make sure that your project references the respective assembly files.

I had the imports statement present in my code prior to your suggesting I add it.

So why the errors?

Please add

Imports Infragistics.Web.UI.ListControls

so that you resolve the errors.

And you dont have to build the list each time. Actually, the SelectionChanged will fire only once by default, when a postback is triggered by any action (form submission for example). I think this works for your scenario. If, however, you have the SelectionChanged postback flag set to ON:

<ig:WebDropDown ID="WebDropDown1 ...>
<AutoPostBackFlags SelectionChanged="On"/>

then the event will fire for every selection. In this case you may build the collection of values at another point, by iterating the this.WebDropDown1.SelectedItems collection.

In Visual Studio 2017, as soon as I add a handler for the WebDropDown1.SelectionChanged, my project blows up with 26 errors even with no code in the handler.

Any idea why I would get so many errors?

I am guessing that because your example uses SelectionChanged, I have to build the list each time the selection changes rather than being able to access the entire list at some point during form submission without the use of this handler.  I was hoping the control would maintain this on it's own.

Great!  I'll check that out.  Thank-you.