Is it possible to programmatically invoke the popup?
I have some operations where I'd like to use the popup to give user feedback. I was wondering if this is currently possible.
If not, it would be a great addition to be able to programmatically open and close the popup
Currently there isn't a way to do that - the excel addin calls your server synchronously. Allowing asynchronous interaction between the addin and server would add quite a bit of complication to its design.
I was thinking of adding the ability to set a message for each function that is registered (ie. what is returned in the GetFunctions call), which would be displayed to the user instead of the default one.
Another option you have is to simply return a message from your function to excel - this would then be displayed in the cell that invokes the function (saying something like "Calculating…"). The user would then refresh the cell or page at a later time to pick up the calculated values.