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Interaction Transition

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Interaction Transition

为了自定义交互式的过渡动画，UIViewControllerTransitioningDelegate对象必须实现对应的协议方法，interactionControllerForPresentation(_:)和interactionControllerForDismissal(_:)。交互控制根据用户的手势输入来更新自定义的过渡动画，
而自定的过度动画是实现了UIViewControllerAnimatedTransitioning协议的对象，关于该协议这里就不再说明了。

Apple提供了一个交互式控制器的具体实现UIPercentDrivenInteractiveTransition，在大多数情况下，我们的交互式控制器只要继承它，然后加入自己的手势交互就好了。

在我们的手势交互逻辑中，根据用户的输入，我们利用以下几个方法来实时更新动画：

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func updateInteractiveTransition(_ percentComplete: CGFloat)

func cancelInteractiveTransition()

func finishInteractiveTransition()

一个简单的例子如下：

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import UIKit

class SwipeInteractionController: UIPercentDrivenInteractiveTransition {
    var interactionInProgress : Bool = false
    private var shouldCompleteTransition : Bool = false
    private weak var viewController : UIViewController!
    
    func wireToViewController(viewController : UIViewController!) {
        self.viewController = viewController
        prepareGestureRecognizerInView(viewController.view)
    }
    
    
    func handleGesture(gestureRecognizer : UIScreenEdgePanGestureRecognizer) {
        let translation = gestureRecognizer.translationInView(gestureRecognizer.view!.superview)
        var progress = translation.x / 200.0
        progress = CGFloat(fminf(fmaxf(Float(progress), 0.0), 1.0))
        
        switch gestureRecognizer.state {
        case .Began:
            interactionInProgress = true
            viewController.dismissViewControllerAnimated(true, completion: nil)
        case .Changed:
            shouldCompleteTransition = progress > 0.5
            updateInteractiveTransition(progress)
        case .Cancelled:
            shouldCompleteTransition = false
            interactionInProgress = false
            cancelInteractiveTransition()
        case .Ended:
            interactionInProgress = false
            
            if shouldCompleteTransition {
                finishInteractiveTransition()
            } else {
                cancelInteractiveTransition()
            }
            
        default:
            print("Unsupported")
        }
        
    }
    // MARK: private 
    private func prepareGestureRecognizerInView(view : UIView) {
        let edgeRecognizer = UIScreenEdgePanGestureRecognizer(target: self, action: #selector(handleGesture))
        edgeRecognizer.edges = UIRectEdge.Left
        view.addGestureRecognizer(edgeRecognizer)
    }
}

在定义了这个Animator之后，只要在另外一个对象（实现了UIViewControllerTransitioningDelegate协议）的interactionControllerForDismissal(_:)返回这个类的实例即可。

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func interactionControllerForDismissal(animator: UIViewControllerAnimatedTransitioning) -> UIViewControllerInteractiveTransitioning? {
        return swipeAnimator.interactionInProgress ? swipeAnimator : nil
    }