ios10: viewDidLoad frame width/height not initialized correctly

The most common issues you describe are appearing in iOS 10 only and can be solved by adding this line (if necessary):

self.view.layoutIfNeeded()

just above the code, that is responsible for changing constraint, layer.cornerRadius etc.

OR

place your code related to frames / layers into viewDidLayoutSubviews() method:

override func viewDidLayoutSubviews() {

    super.viewDidLayoutSubviews()
    view.layer.cornerRadius = self.myView.frame.size.width/2
    view.clipsToBounds = true

    ... etc
}