转场（transition）动画
1.转场种类
分为4种：present,dismiss; push, pop.
前两者是presentViewController时的方式.
后两者是在navigationController中的方式.
2.针对不同种类的转场动画
（1）对于前两者, 需要实现UIViewControllerTransitioningDelegate,
并在viewController中设置该delegate.
设置transitioningDelegate：
override func viewDidLoad() {
super.viewDidLoad()
self.transitioningDelegate = self
}
实现UIViewControllerTransitioningDelegate：
extension GreenViewController: UIViewControllerTransitioningDelegate {
func animationController(forDismissed dismissed: UIViewController) -> UIViewControllerAnimatedTransitioning? {
return ShapeAnimator(duration: TimeInterval(animationDurationSlider.value), viewCenter: self.view.center, viewSize: self.view.bounds.size, startPoint: self.transitionButton.center, transitionMode: .push)
}
func animationController(forPresented presented: UIViewController, presenting: UIViewController, source: UIViewController) -> UIViewControllerAnimatedTransitioning? {
return ShapeAnimator(duration: TimeInterval(animationDurationSlider.value), viewCenter: self.view.center, viewSize: self.view.bounds.size, startPoint: self.transitionButton.center, transitionMode: .push)
}
}
forPresented 和 forDismissed 方法 分别对应present 和 dismiss.
注意到方法有返回值，且返回值类型为UIViewControllerAnimatedTransitioning
这实际上就是转场动画需要实现的协议,转场动画的关键也在于此.
下文会着重讲解这个部分.
(2)对于后两者，需要实现UINavigationControllerDelegate,并在ViewController中设置navigationController的delegate.
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
self.navigationController?.delegate = self
}
实现UINavigationControllerDelegate
extension GreenViewController: UINavigationControllerDelegate {
func navigationController(_ navigationController: UINavigationController, animationControllerFor operation: UINavigationControllerOperation, from fromVC: UIViewController, to toVC: UIViewController) -> UIViewControllerAnimatedTransitioning? {
if operation == .push {
if isAnimationSpring {
return SpringAnimator(duration: TimeInterval(animationDurationSlider.value), velocity: CGFloat(initialVelocitySlider.value), damping: CGFloat(springSlider.value))
} else {
return ShapeAnimator(duration: TimeInterval(animationDurationSlider.value), viewCenter: fromVC.view.center, viewSize: fromVC.view.bounds.size, startPoint: self.transitionButton.center, transitionMode: .push)
}
} else {
return nil
}
}
}
push以及pop的类型可以通过operation获取.
同样针对不同的类型，也需要返回实现了UIViewControllerAnimatedTransitioning的对象.
所以，核心就是封装一个实现了UIViewControllerAnimatedTransitioning的对象.
而这个对象是可以在present／navigate动画中复用的.
3.封装一个实现UIViewControllerAnimatedTransitioning的对象.
直接上代码：
关键就是实现UIViewControllerAnimatedTransitioning的协议,
transitionContext是转场的上下文,
可以通过它获取到动画容器视图，转场前的视图，转场后的视图.
并在动画容器视图中实现动画效果即可.
在transitionDuration()可以设置转场动画的时长.
import UIKit
class SpringAnimator: NSObject {
var animationDuration: TimeInterval = 2
var initialVelocity: CGFloat = 0
var springDamping: CGFloat = 0.4
convenience init(duration: TimeInterval, velocity: CGFloat, damping: CGFloat) {
self.init()
animationDuration = duration
initialVelocity = velocity
springDamping = damping
}
}
extension SpringAnimator: UIViewControllerAnimatedTransitioning {
func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
return animationDuration
}
func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
let toViewController = transitionContext.viewController(forKey: UITransitionContextViewControllerKey.to)
let containerView = transitionContext.containerView
let fromView = transitionContext.view(forKey: UITransitionContextViewKey.from)
let toView = transitionContext.view(forKey: UITransitionContextViewKey.to)
toView?.frame = fromView?.frame.offsetBy(dx: 0, dy: -(fromView?.frame.size.height ?? 0)) ?? .zero
toView?.alpha = 0
containerView.addSubview(toView!)
let duration = self.transitionDuration(using: transitionContext)
UIView.animate(withDuration: duration, delay: 0, usingSpringWithDamping: springDamping, initialSpringVelocity: initialVelocity, options: .curveLinear, animations: {
toView!.alpha = 1.0
toView?.frame = transitionContext.finalFrame(for: toViewController!)
}) { (isFinished) in
let wasCancelled = transitionContext.transitionWasCancelled
transitionContext.completeTransition(!wasCancelled)
}
}
}
至此，一个转场动画效果就封装好啦，demo可以去我的github下载：https://github.com/LoKiLyn/TransitionAnimation
