How to convert a CGPoint in one UIView to another view using convert()

Written by Paul Hudson    @twostraws

Each view has its own co-ordinate system, meaning that if I tap a button and ask iOS where I tapped, it will tell me where I tapped relative to the top-left of the button. This is usually what you want, but if you want to translate a position in one view into a position it's easy enough to do.

As an example, this code creates two views, creates a virtual "tap", then converts it from the first view's co-ordinate space to the second's:

let view1 = UIView(frame: CGRect(x: 50, y: 50, width: 128, height: 128))
let view2 = UIView(frame: CGRect(x: 200, y: 200, width: 128, height: 128))

let tap = CGPoint(x: 10, y: 10)
let convertedTap = view1.convert(tap, to: view2)

That will set convertedTap to X -140.0, Y -140.0.

Available from iOS 2.0

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