https://github.com/robertmryan/autolayout-category

https://github.com/danramteke/DRAutolayout

https://github.com/robotmedia/Lyt

https://github.com/mobitar/AutolayoutHelpers

https://github.com/HomeSchoolDev/MAConstraint

https://github.com/codesourse/autolayout

https://github.com/yaole/AutoLayout

https://github.com/yaoqi-github/AutoLayout

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http://stackoverflow.com/questions/142282/how-do-i-tell-if-a-uiview-is-visible-and-on-screen