I am trying to create a custom form control that will allow the selection of multiple documents to store in a field for Web parts. This form control type exists in the Umbraco CMS, but not in Kentico, which I find quite annoying and unbelievable.

I want something that works similar to the ClassNames selector but I want it to select documents like the Document selector does and I want it to display the selected documents in a UniGrid.

After reading the documentation here, I understand that the uniselector control can be configured to display selected items in a unigrid if I set the selectionmode to "multiple"

To test out the settings, I temporarily changed the SelectionMode of the ClassNames form control to "Multiple" and set the GridName property to the location of an xml file

I don't have a complete understanding of how to configure the UniGrid with the xml file, so I didn't put anything in the columns, hoping that it would autogenerate them.

When I loaded a wep part configuration window, I immediately got the error "The control collection cannot be modified during DataBind, Init, Load, PreRender or Unload phases." I also get this error when I omit the GridName property.

I don't have the time to learn everything about the UniGrid and the UniSelector by messing around with them, so I am hoping that someone can help me.

Does anyone have an example or know where I can find an example where a UniSelector is used with SelectionMode = Multiple?

Also, If any of you Kentico devs out there who know the UniGrid and UniSelector really well and want to quickly whip together a custom form control that allows selection of multiple documents and stores their document ids in a delimited list like the classnames form control, please do so and send it my way.

Thanks!