Is it okay to change UI in the OnActivated event on iPhone in CocoaTouch?

Is one allowe开发者_StackOverflow社区d to change/setup the UI in the applications OnActivated event? It seems like I get sometimes incorrect screen setups and wonder if it is actually allowed what I'm doing.

The Apple documentation states, "If your application was previously in the background, you could also use it [applicationDidBecomeActive] to refresh your application’s user interface."