How to show waiting dialog while navigating in storyboard?

Hi all,

I want to use UIActivityIndicatorView to show as a dialog in order to give a note to the users that the progress is going on, while the second screen is too slow to rendering.

But when I try to put code into PrepareForSegue event handler, it don't shows the dialog until the next screen is shown.

How to do it? Thank you very much.