iOS 3.x support in Xcode 4

Question

Is it possible to write apps that support iOS 3.x versions using Xcode 4? If so, how? And does Apple have any official recommendations on app backwards-compatibility?

Answer 1

To get your app successfully run in iOS 3.x device, follow these steps (Xcode 4.2):

1. Click on your project name, select your Target and under "Build Settings"

   a) Set "iOS development target" (under "Deployment") to 3.0

   b). Add "armv6" to list of "Architectures" (under "Architectures").

   c) Set "Other Linker Flags" (under "Linking") to "-weak-lSystem".

2. In your Info.plist file remove value of "armv7" from "Required device capabilities" (UIRequiredDeviceCapabilities).

3. In your code:

   a). Do not use userInterfaceIdiom. If you need to know, what device is it (iPhone or iPad), see How does one get UI_USER_INTERFACE_IDIOM() to work with iPhone OS SDK < 3.2.

   b) Do not use window.rootViewController. Instead use [window addSubview: self.mainViewController.view]; to add your main controller's view to window.

4. Click on your project name, select your Target and under "Build Phases" / "Link Binary With Libraries" set "UIKit.framework" to "Optional". Also set to optional any extra framework, which is not available in iOS 3. For example, if you're using iAd or Twitter frameworks they should be set to optional. Check availability of extra framework in your code before use.

5. When run on real device, compile app against last version of SDK. To do so, select second item from "Scheme" drop down (otherwise you'll get compile error related to your optional SDKs):

Answer 2

Yes, you can develop apps that support previous iOS versions with the current iOS SDK.

For official recommendations, see Apple's SDK Compatibility Guide.