I have a UIView as a XIB in Portrait mode.
This view is added programmatically to the viewcontroller like this:
NSArray *nibObjects = [[NSBundle main
See this related question:
When do autoresizing masks take effect in iOS?
So after loading your new view from the nib, and adding as a subview to self.view, try calling setNeedsLayout.
self.view
setNeedsLayout