NSLayoutConstraint 开源框架

https://github.com/cloudkite/Masonry

Masonry is a light-weight layout framework which wraps AutoLayout with a nicer syntax. Masonry has its own layout DSL which provides a chainable way of describing your NSLayoutConstraints which results in layout code that is more concise and readable. Masonry supports iOS and Mac OSX.

For examples take a look at the Masonry iOS Examples project in the Masonry workspace.

https://github.com/smileyborg/UIView-AutoLayout

The ultimate API for creating Auto Layout constraints -- impressively simple, immensely powerful. Comprised of categories on UIView, NSArray, and NSLayoutConstraint.

UIView+AutoLayout was designed to provide a developer-friendly interface for the vast majority of Auto Layout use cases. It's optimized for clarity and simplicity while simultaneously minimizing the amount of third party code. The API takes inspiration from the Auto Layout UI options available in Interface Builder, but delivers far more flexibility and capability.

https://github.com/iMartinKiss/KeepLayout

Keep Layout is project under active development whose purpose is to make Auto Layout much easier to usefrom code! No more Interface Builder or Visual Format. Keep Layout provides simple, more readable and powerful API for creating and accessing existing constraints.

Before you start, you should be familiar with Auto Layout topic. How it works and what's the point?