Is there a way to install older iOS SDKs in Xcode?

I'd like to ensure some backward compatibility for my apps by compiling them using the older SDKs to test for newer classes and methods. However, Xcode is only available with SDKs for the latest iOS versions.

I've downloaded and installed the iOS 3.1.3 SDK (using the method described here) and that works fine. My code is full (not so full :-) ) of __IPHONE_OS_VERSION_MAX_ALLOWED, __IPHONE_OS_VERSION_MIN_REQUIRED开发者_如何学C and such respondsToSelector.

This works right now for the iOS 3.1.3 SDK, but what if in the future I wanted to repeat this process with the 4.0 SDK? Is there a general process for installing older SDK versions in the latest Xcode?

You can't install old 3.1 SDKs on Xcode 4. You can set the Deployment target lower to allow testing on devices running older OS versions than your current SDK installation. The only current way to completely ensure backward compatibility, while running more recent versions of Xcode, is to keep a device that runs iOS 3.x, and test on that device. (...because it is claimed that the old Simulators/tools sometimes actually allows APIs that won't run on an actual device with an OS of the same version).

Other methods include installing the different versions of iOS developer tools in a separate Developer_XYZ directories, and or keeping around a bootable HD with the older iOS developer tool installation (say Snow Leopard with Xcode 3.x, since Lion might only support running Xcode 4.x).

For whatever reason (I had to do it to debug an Apple bug), if you still need to install an older SDK to your existing Xcode, follow these steps :

• Install the older Xcode package
• Copy the older Xcode SDK to the new Xcode Example (/old/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS5.1.sdk to /new/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs)
• Restart your 'new' Xcode
• You will see the old SDK in the build setting option (base sdk)