BHMenuInteractionGesture.swift

fileprivate let threshold : CGFloat = 300
@objc func handlePanGesture(sender: UIPanGestureRecognizer) {
    let view = sender.view!
    let viewTranslation = sender.translation(in: view)
    switch sender.state {
    case .began:
        transitionInProgress = true
        presentedViewController.dismiss(animated: true, completion: nil)
        break
    case .changed:
        guard viewTranslation.x < 0 else {
            cancel()
            return
        }
        let absX = abs(viewTranslation.x)
        const = CGFloat(fminf(fmaxf(Float(absX / threshold), 0), 1.0))
        shouldCompleteTransition = const > 0.5
        update(const)
        break
    case .cancelled, .ended , .failed:
        if !shouldCompleteTransition || sender.state == .cancelled {
            cancel()
        } else {
            finish()
        }
        transitionInProgress = false
        break
    default:
        transitionInProgress = false
        break
    }
}