iPhone upside down

ViewController.swift

// MARK: Allow iPhone to work upside-down
extension ViewController {
    // allow the iPhone to work upside down; by default on the iPhone this method returns UIInterfaceOrientationMaskAllButUpsideDown
    // http://stackoverflow.com/questions/12542472/why-iphone-5-doesnt-rotate-to-upsidedown/12758715#12758715
    override func supportedInterfaceOrientations() -> UIInterfaceOrientationMask {
        return UIInterfaceOrientationMask.All
    }
}

For Swift 3 it becomes:

override public var supportedInterfaceOrientations: UIInterfaceOrientationMask {
    return [.landscape]
}

also I found I need to add the above to UINavigationController if the app uses one
and also check "Requires full screen" on the iPad
see: http://stackoverflow.com/questions/35274428/supportedinterfaceorientations-not-called-in-ipad