程序不输出转换后的整数

Question

我目前有一个程序，我的目标是创建一个可以将整数转换为字符串的函数，这里是：

import UIKit
class Transitioning: NSObject, UIViewControllerAnimatedTransitioning {

    func transitionDuration(transitionContext: UIViewControllerContextTransitioning?) -> NSTimeInterval {
        return 0.5
    }

    func animateTransition(transitionContext: UIViewControllerContextTransitioning) {
        let fromView = transitionContext.viewForKey(UITransitionContextFromViewKey)
        let toView = transitionContext.viewForKey(UITransitionContextToViewKey)
        let containerView = transitionContext.containerView()
        if let fromView = fromView, toView = toView {
            containerView?.addSubview(fromView)
            containerView?.addSubview(toView)

            toView.alpha = 0
            UIView.animateWithDuration(0.5, animations: {
                toView.alpha = 1
            }, completion: {
                finished in
                transitionContext.completeTransition(true)
            })
        }
    }
}

然而，这不会向控制台输出任何结果。我希望它输出字符串“10”。我对c ++比较陌生，所以任何帮助都会受到赞赏。