Use autolayout on view added to UIWindow

Question

I'm trying to add a subview to the keyWindow of the app, and position it using autolayout. However, autolayout doesn't seem to work at all, whereas setting a frame does. I want to align my view infoSc to the bottom of the keyWindow using the following code:

let infoSc = InfoScreenView()
infoSc.translatesAutoresizingMaskIntoConstraints = false

let keyWindow = UIApplication.sharedApplication().keyWindow!
keyWindow.addSubview(infoSc)
keyWindow.addConstraint(NSLayoutConstraint(item: infoSc, attribute: .Left, relatedBy: .Equal, toItem: keyWindow, attribute: .Left, multiplier: 1, constant: 0))
keyWindow.addConstraint(NSLayoutConstraint(item: infoSc, attribute: .Right, relatedBy: .Equal, toItem: keyWindow, attribute: .Right, multiplier: 1, constant: 0))
keyWindow.addConstraint(NSLayoutConstraint(item: infoSc, attribute: .Bottom, relatedBy: .Equal, toItem: keyWindow, attribute: .Bottom, multiplier: 1, constant: 0))
infoSc.addConstraint(NSLayoutConstraint(item: infoSc, attribute: .Height, relatedBy: .Equal, toItem: nil, attribute: .NotAnAttribute, multiplier: 1, constant: 100))

However, it appears to have a frame of CGRectZero using this method. Any ideas how to make this work? Ideally I'd also want to align it to something that's inside self.view too, but that throws an error that self.view is not in the view hierarchy of keyWindow.

Answer 1

If you need to draw on the entire window, here is code to do it (in this example I am in the AppDelegate, so window is the AppDelegate.window property).

func tryToDrawOnTheWindow()
{
    if let window = window, view = window.rootViewController?.view
    {
            print("I have a root view")

            let infoSc = InfoScreenView(frame: view.frame)
            let count = view.subviews.count
            view.insertSubview(infoSc, atIndex: count)
            infoSc.translatesAutoresizingMaskIntoConstraints = false
            let height = NSLayoutConstraint(item: infoSc, attribute: .Height, relatedBy: .Equal, toItem: view, attribute: .Height, multiplier: 1, constant: 0)
            let width = NSLayoutConstraint(item: infoSc, attribute: .Width, relatedBy: .Equal, toItem: view, attribute: .Width, multiplier: 1, constant: 0)
            let offset = NSLayoutConstraint(item: infoSc, attribute: .Top, relatedBy: .Equal, toItem: view, attribute: .Top, multiplier: 1, constant: 0)
            print([height, width, offset])
            view.addConstraints([height, width, offset])
    }
    else
    {
        print("No root view on which to draw")
    }
}

This will let you draw on top of whatever is in the view hierarchy. In my test app, I added a textfield and a blue rect, and the overlay was orange with 40% opacity. Bear in mind that by default the overlay view will consume all taps in this case.