In some ways, iOS 7 is the most radical change to iOS since the software development kit (SDK) was released in iPhone OS 2. The press and blogosphere have discussed every aspect of the new “flat” user interface and what it means for app developers and users. Suffice to say, no iOS upgrade has required so many developers to redesign their UI so much.
But in other ways, iOS 7 is a nearly seamless transition from iOS 6. Compared to the multitasking changes in iOS 4, iOS 7 may require very little change to your apps, particularly if you have either a very standard UI or a completely custom UI. For those on the extremes, the UI changes are either nearly free or irrelevant.
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iOS 7 Programming Pushing the Limits
原文：http://www.cnblogs.com/521tanshijia/p/4777286.html