How to get device width and height?

I haven't tried but it should be..

var bounds = UIScreen.main.bounds
var width = bounds.size.width
var height = bounds.size.height

Swift 4.2

let screenBounds = UIScreen.main.bounds
let width = screenBounds.width
let height = screenBounds.height

@Houssni 's answer is correct, but since we're talking Swift and this use case will come up often, one could consider extending CGRect similar to this:

extension CGRect {
    var wh: (w: CGFloat, h: CGFloat) {
        return (size.width, size.height)
    }
}

Then you can use it like:

let (width, height) = UIScreen.mainScreen().applicationFrame.wh

Hooray! :)