If you compile using Xcode 4.2, and default-ed iOS 5.0, you will find that when you come to the scenario which you need to run on earlier devices, e.g. iPhone 3GS, iPod 2/3, i.e. at most iOS 4.2.1. The code will be compiled and run, but nothing happen, the app didn’t run, but the status shown on Xcode is “Finished Running [app] on [device]".
To solve this, you need to change two field.
1. Build Settings -> Search “Architectures". Default is “armv7″. You should add a field and type in “armv6″ (which is for earlier devices.)
2. Open your Info.plist file. Change the “Required device capabilities" to armv6, or just remove it.
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