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

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

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

Answer 2

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 3

to be sure, you can use Xcode 4 for targeting iOS 3.x as a deployment target, but you will not be able to simulate your program on a iOS 3.x SDK simulator. So you are pretty on your own (i.e., if you use any iOS 4.x-only feature, you will not find out it until you test on a physical device).

You need an older version of Xcode to debug against an older simulated SDK.

Answer 4

The version of Xcode that you use isn't related to the version of iOS that your app can support. To choose the version of iOS that your app supports, simply change the iOS deployment target in your project settings. Then just be sure not to use any APIs from versions later than that.