I have iPhone application in the App Store. Do I have to compile my app with iOS 4.2 SDK in order to allow it run on iOS 4.2 devices? Or compiling using iOS 4.2 is required only to allow using new features of new iOS?
I will appreciate if you can clarify this issue...
Thanks! Yoash
Do I have to compile my app with iOS 4.2 SDK in order to allow it run on iOS 4.2 devices?
No, it will run on the new firmare just fine. At least if the new firmare does not reveal some bugs in your code (which happens).
You don't need to recompile it to let it run on newer OS versions, but like you already guessed, you need to recompile it when you want to use the newer features (eg. AirPlay, "Multitasking" etc).
The old version should still run.
The app might not play well with new features like multitasking on iPad, so it is worthwhile trying to get some testing and feedback done as soon as you can in case there are issues.
If you download the XCode 4 pre-release from the developer portal, you can use the new static analyser to look for problems in the code: this is not just for SDK issues but also things like memory leaks.
Apple recommends that you always compile with the latest SDK, even if you are targeting older versions.
Unless you run into a specific issue that is causing incompatibilities, it is wise to take this advice. A lot of small bugs and performance issues are fixed with each new iteration of the SDK.
That being said - you can continue to use the older SDK's, and Apple will still accept the apps you build. For mature apps that are only going through minor tweaks, this is probably the safest course to avoid introducing new bugs.
