Attribute Unavailable: Automatic Preferred Max Layout Width is not available on iOS versions prior t

测试环境：Xcode6.1.1

警告：Attribute Unavailable: Automatic Preferred Max Layout Width is not available on iOS versions prior to 8.0

解决方案：打开Main.storyboard，选择File inspector，找到Interface Builder Document下的Builds for，选择iOS8 .0 and Later。

注：该答案来自于：http://www.cocoachina.com/bbs/read.php?tid=226246，5L正解

示意图：