// define a variable to store initial touch position
var initialTouchPoint: CGPoint = CGPoint(x: 0,y: 0)

@IBAction func panGestureRecognizerHandler(_ sender: UIPanGestureRecognizer) {
    let touchPoint = sender.location(in: self.view?.window)

    if sender.state == UIGestureRecognizerState.began {
        initialTouchPoint = touchPoint
    } else if sender.state == UIGestureRecognizerState.changed {
        if touchPoint.y - initialTouchPoint.y > 0 {
            self.view.frame = CGRect(x: 0, y: touchPoint.y - initialTouchPoint.y, width: self.view.frame.size.width, height: self.view.frame.size.height)
        }
    } else if sender.state == UIGestureRecognizerState.ended || sender.state == UIGestureRecognizerState.cancelled {
        if touchPoint.y - initialTouchPoint.y > 100 {
            self.dismiss(animated: true, completion: nil)
        } else {
            UIView.animate(withDuration: 0.3, animations: {
                self.view.frame = CGRect(x: 0, y: 0, width: self.view.frame.size.width, height: self.view.frame.size.height)
            })
        }
    }
}