Showing a "loading" message for long operations

Forgive me if this is obvious or pointed out in docs but I cannot find any mention of it.

in my app when they select an option, there is a http fetch operation that takes at least a few seconds. I want to display a “loading” message while this happens so they dont’ click over and over…

how is this done?

the only thread I found that mentioned this said to use screen.ShowMessage(“Retrieving…”), but not sure how to use it. I tried m.screen.ShowMessage(“Retrieving…”) and received the error:

Interface not a member of BrightScript Component (runtime error &hf3)

which I assume means I’m using it incorrectly. can someone point me to the docs or more info on the correct way to do this?

many thanks