我希望在我的应用程序中，能够滑动进入和退出视图控制器。因此，我正在使用自定义转换，但应用程序崩溃了。我无法确定确切的问题所在，请帮助我解决。
代码
class CustomTransition: NSObject, UIViewControllerAnimatedTransitioning,UIViewControllerTransitioningDelegate {
func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
// get reference to our fromView, toView and the container view that we should perform the transition in
let container = transitionContext.containerView
let fromView = transitionContext.view(forKey: UITransitionContextViewKey.from)! // the app crashes here saying nil founded
let toView = transitionContext.view(forKey: UITransitionContextViewKey.to)!
let animationDuration = self .transitionDuration(using: transitionContext)
let offScreenRight = CGAffineTransform(translationX: container.frame.width, y: 0)
let offScreenLeft = CGAffineTransform(translationX: -container.frame.width, y: 0)
toView.transform = offScreenRight
// add the both views to our view controller
container.addSubview(toView)
container.addSubview(fromView)
UIView.animate(withDuration: animationDuration, delay: 0.0, usingSpringWithDamping: 0.5, initialSpringVelocity: 0.8, options: [] , animations: {
fromView.transform = offScreenLeft
toView.transform = CGAffineTransform.identity
}, completion: { finished in
// tell our transitionContext object that we've finished animating
transitionContext.completeTransition(true)
})
}
func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
return 1
}
func animationController(forPresented presented: UIViewController, presenting: UIViewController, source: UIViewController) -> UIViewControllerAnimatedTransitioning? {
return self
}
func animationController(forDismissed dismissed: UIViewController) -> UIViewControllerAnimatedTransitioning? {
return self
}
}
我是如何使用的
let vc = self.getViewControllerFromStoryBoard(storyBoardName: FORGOT_PASSWORD_SB, identifier: FORGOT_PASSWORD_IDENTIFIER) as! ForgotPassword
let a = CustomTransition()
vc.transitioningDelegate = a
vc.modalPresentationStyle = .custom
self.present(vc, animated: true, completion: nil)
这个应用程序崩溃了，提示“找不到nil”，
let fromView = transitionContext.view(forKey: UITransitionContextViewKey.from)! 有什么问题吗？请问我漏掉了什么东西吗？