Home How do I add constraints to a subview loaded from a nib file?
 I'm trying to load a sub view on to every single page of my app from a nib file. Right now I'm using a somewhat unusual approach to loading this sub view in that I am doing it through an extension of UIStoryboard (probably not relevant to my problem, but I'm not sure). So this is how the code looks when I load the nib file: extension UIStoryboard { public func appendCustomView(to viewController: UIViewController) { if let myCustomSubview = Bundle.main.loadNibNamed("MyCustomSubview", owner: nil, options: nil)![0] as? MyCustomSubview { viewController.view.addSubview(myCustomSubview) } } }  This code does what it's supposed to do and adds "MyCustomSubview" to the view controller (I won't go in to detail on exactly how this method gets called because it works so it doesn't seem important). The problem is I can't for the life of me figure out how to add constraints that effect the size of myCustomSubview. I have tried putting code in the function I showed above as well as in the MyCustomSubview swift file to add constraints but no matter what I do the subview never changes. Ideally the constraints would pin "MyCustomSubview" to the bottom of the ViewController, with width set to the size of the screen and a hard coded height constraint. Here are the two main methods I tried (with about 100 minor variations for each) that did NOT work: Method 1 - Add constraint directly from "appendCustomView" public func appendCustomView(to viewController: UIViewController) { if let myCustomSubview = Bundle.main.loadNibNamed("MyCustomSubview", owner: nil, options: nil)![0] as? MyCustomSubview { let top = NSLayoutConstraint(item: myCustomSubview, attribute: .top, relatedBy: .equal , toItem: viewController.view, attribute: .top, multiplier: 1, constant: 50.0) viewController.view.addSubview(myCustomSubview) viewController.view.addConstraint(top) } }  Method 2 - Add constraint outlets and setter method in MyCustomSubview class MyCustomSubview: UIView { @IBOutlet weak var widthConstraint: NSLayoutConstraint! @IBOutlet weak var heightConstraint: NSLayoutConstraint! func setConstraints(){ self.widthConstraint.constant = UIScreen.main.bounds.size.width self.heightConstraint.constant = 20 } }  And call setter method in "appendCustomView" public func appendCustomView(to viewController: UIViewController) { if let myCustomSubview = Bundle.main.loadNibNamed("MyCustomSubview", owner: nil, options: nil)![0] as? MyCustomSubview { myCustomSubview.setConstraints() viewController.view.addSubview(myCustomSubview) } }  (*note: the actual constraints of these examples are irrelevant and I wasn't trying to meet the specs I mentioned above, I was just trying to make any sort of change to the view to know that the constraints were updating. They weren't.) Edit : Changed "MyCustomNib" to "MyCustomSubview" for clarity.