You definitely need to watch a WWDC 2012 video about Auto Layout on developer.apple.com. Videos:
- Session 202 - Introduction to Auto-Layout for iOS and OS X
- Session 228 - Best Practices for Mastering Car Dealerships
- Session 232 - Example Auto-Layout
The videos show how to set limits in the code using the visual description language and in IB. They also cover some of the "gotchas" when switching to Auto-Layout.
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