iOSAutoLayoutDebug

po [[UIWindow keyWindow] _autolayoutTrace] // prints layouts ambiguity
po [view constraintsAffectingLayoutForAxis:0] // horizontal
po [view constraintsAffectingLayoutForAxis:1] // vertical

[view hasAmbiguousLayout] // BOOL
[view exerciseAmbiguityInLayout] // visualizing ambiguity

viewController.extendedLayoutIncludesOpaqueBars = NO;
viewController.automaticallyAdjustsScrollViewInsets = NO;
viewController.edgesForExtendedLayout = UIRectEdgeNone;

navigationBar.translucent = NO;