问题 The iOS 9 readableContentGuide is a UILayoutGuide (essentially, a thing you can pin constraints to) that all UIViews have. The idea is to keep subviews with text from being too wide on iPad in landscape. It's easy to configure this in code ( v1 is the subview, v is its superview): NSLayoutConstraint.activateConstraints([ v1.topAnchor.constraintEqualToAnchor(v.readableContentGuide.topAnchor), v1.bottomAnchor.constraintEqualToAnchor(v.readableContentGuide.bottomAnchor), v1.rightAnchor