I don't want my app to run on an iPhone or iPod with any OS prior to 3.0. I was under the impression that the App store would take care of it for me, but I don't think that is the case.
What is the best way to alert the user and then quit? Preferably, I'd like this to happen before the user purchases my app, but if the fact is that a user has my app, and an old iPod or iPhone, I need to keep the app from crashing.
You can check for
float version = [[[UIDevice currentDevice] systemVersion] floatValue];
and then display a UIAlertView. But the App won't even start, because OS requirement you set in your project settings.
But remember: The User will be still able to download it.
来源：https://stackoverflow.com/questions/2054963/can-i-prevent-an-iphone-os-3-x-app-from-running-on-2-x-os