摘要：
参考资料https://developer.apple.com/library/mac/documentation/UserExperience/Conceptual/AutolayoutPG/VisualFormatLanguage/VisualFormatLanguage.html#//apple_ref/doc/uid/TP40010853-CH3https://developer.apple.com/library/ios/technotes/tn2154/_index.htmlhttps://developer.apple.com/library/mac/documentation/ 阅读全文