How to show loading message when making a ajax call in controller

How to show loading message when making a ajax call in controller

I have a Rhomobile Application, where i need some data to fetch from the
server in the controller.
I have been using the below code,
result = Rho::AsyncHttp.get(
:url => "http://www.example.com/API-vs-1"
)
@get_result = res["body"]
When i basically do a ajax call in javascript, i do have a
LoadingMessage() and HideMessage() function which makes the loading
screen.
So how and where can i do shomething to show a loading screen in here.