viewDidLoad.swift

override func viewDidLoad() {
                
    previewView = UIView(frame: CGRect(x:0, y:0, width: UIScreen.main.bounds.size.width, height: UIScreen.main.bounds.size.height))
    previewView.contentMode = UIView.ContentMode.scaleAspectFit
    view.addSubview(previewView)
    
    cameraController.prepare {(error) in
        if let error = error {
            print(error)
        }
        
        try? self.cameraController.displayPreview(on: self.previewView)
    }
    
}