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假設我有一個UINavigationController，我想在其上執行自定義轉換。爲了方便起見，我定義了一個過渡類：帶兩個代表的UINavigationController？
class WTPTransition: NSObject
{
// This is our Interaction Controller, which conforms to UIViewControllerInteractiveTransitioning. Apple's concrete class suits our needs.
var interactionController : UIPercentDrivenInteractiveTransition?
}
extension WTPTransition : UIViewControllerAnimatedTransitioning
{
func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
return 1
}
func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
let toView = transitionContext.viewController(forKey: .to)!.view!
let fromView = transitionContext.viewController(forKey: .from)!.view!
transitionContext.containerView.insertSubview(toView, belowSubview: fromView)
UIView.animate(withDuration: transitionDuration(using: transitionContext), animations: {
fromView.alpha = 0.0
}, completion: { finished in
transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
})
}
}
然後我擴展它，這樣我可以簡單地設置一個UINavigationController的delegate財產，讓我轉換：
extension WTPTransition : UINavigationControllerDelegate
{
func navigationController(_ navigationController: UINavigationController, animationControllerFor operation: UINavigationControllerOperation, from fromVC: UIViewController, to toVC: UIViewController) -> UIViewControllerAnimatedTransitioning? {
return self
}
func navigationController(_ navigationController: UINavigationController, interactionControllerFor animationController: UIViewControllerAnimatedTransitioning) -> UIViewControllerInteractiveTransitioning? {
return interactionController
}
}
這工作得很好，但會發生什麼如果我想要另一個班級觀察相同的導航控制器的事件？我不能有兩個對象作爲它的委託，那麼使用什麼正確的模式？將觀察控制器的轉換邏輯與顯示或解散的東西分開似乎很自然。