问题
Before iOS 7, iPhone apps that opened on iPads used to launch in 2x mode. iOS 7 seems to force all apps, even if they weren't designed for the iPad, to launch in 1x mode. How can we force our app to launch in 2x mode on iPads using iOS 7?
回答1:
iPhone apps on iPads running iOS 7 now always open as a Retina iPhone app, while on iOS 6 they opened as a non-retina apps on non-retina iPads.
On Retina iPads (iPad 3 and 4) the apps may display in 1x (iPhone sized) or 2x (taking as much of the iPad screen as possible) and may be toggled.
On non-Retina iPads (iPad 2 and iPad mini) the apps only display in 2x mode and cannot be toggled. This is because the non-retina iPads do not have enough pixel density to display the retina iPhone apps at the "normal" size.
This behavior is determined by the OS and cannot be changed by your app.
来源：https://stackoverflow.com/questions/18969686/launch-app-on-ipad-in-2x-mode-with-ios-7