Apps compatible with iPhone5 and reverse

Question

I know that an app developed for iPhones older than iPhone5 is working in a letter box. But how about the revers. An app updated to iPhone5 standard. How does it work on iPhone4 ?

If not, when all developers have updated their apps, the older iPhones will be without apps or updates ?

Answer 1

This is more geared toward MonoTouch, but the same techniques apply to Obj-C:

http://redth.info/get-your-monotouch-apps-ready-for-iphone-5-ios-6-today/

Basically the Default-568h@2x.png file will tell iOS that it's a 'Tall' app. For other image assets you need to detect if it's the tall device or not by checking the UIScreen's MainScreen's Bounds as well as if it's an iPhone idiom or not and then seeing if the height is 1136 (checking the scale value), and then selecting a different sized image in this case.

Here's the C# code, but again it's very close to Obj-C:

public static bool IsTall
{
  get 
  { 
    return UIDevice.CurrentDevice.UserInterfaceIdiom 
             == UIUserInterfaceIdiom.Phone 
           && UIScreen.MainScreen.Bounds.Height 
             * UIScreen.MainScreen.Scale >= 1136;
  }     
}