UIKit customized transition API – a theoretical lesson
There are a lot of lessons and delegates concerned in the course of the course of of creating a customized transition, let’s stroll by this stuff actual fast, and do some coding afterwards.
UIViewControllerTransitioningDelegate
Each view controller can have a transition delegate, in that delegate implementation you’ll be able to present the customized animation and interplay controllers. These objects will probably be accountable for the precise animation course of, and this delegate is the place the place you’ll be able to “inject your code” to the UIKit framework. 💉
UINavigationControllerDelegate
The navigation controller delegate additionally has two strategies which are accountable for customized push and pop animations. It is virtually the identical because the transitioning delegate for the view controllers, however you may see this in motion in a while. 💥
UINavigationController.Operation
The navigation controller operation is simply an enum which incorporates the “course” of the navigation animation. Normally push or pop.
Presenting and dismissing one thing modally isn’t precisely the identical factor as pushing & popping view controllers inside a navigation stack. Extra on this later.
UIViewControllerAnimatedTransitioning
These objects are returned by the transition delegate, so principally that is the place the place you implement the flamboyant customized view animations. 😉
UIViewControllerContextTransitioning
This context encapsulates all the data concerning the transitioning, you may get the taking part views, controllers and lots of extra from this object. The transitioning context is on the market so that you can use it in the course of the animation.
UIPercentDrivenInteractiveTransition
An object that drives an interactive animation between one view controller and one other.
In a nutshell, that is the factor that offers you the magical means to swipe a navigation controller interactively again (and forth in the event you modified your thoughts) along with your fingers from the sting of the display screen. 📱
Customized transition animations programmatically
Let’s do some actual coding! I am going to present you the best way to make a fundamental fade animation between view controllers inside a navigation stack. First we’ll begin with the push animation.
open class FadePushAnimator: NSObject, UIViewControllerAnimatedTransitioning {
open func transitionDuration(
utilizing transitionContext: UIViewControllerContextTransitioning?
) -> TimeInterval {
0.5
}
open override func animateTransition(
utilizing transitionContext: UIViewControllerContextTransitioning
) {
guard
let toViewController = transitionContext.viewController(forKey: .to)
else {
return
}
transitionContext.containerView.addSubview(toViewController.view)
toViewController.view.alpha = 0
let period = self.transitionDuration(utilizing: transitionContext)
UIView.animate(withDuration: period, animations: {
toViewController.view.alpha = 1
}, completion: { _ in
transitionContext.completeTransition(
!transitionContext.transitionWasCancelled
)
})
}
}As you’ll be able to see making a customized transition animation is admittedly easy. You simply must implement two delegate strategies. One in every of them will return the period of the animation, and the opposite will comprise the precise transition.
The transition context supplies a customized containterView object that you should use within the animation, additionally you’ll be able to seize the taking part views and controllers from this object as I discussed it earlier than. Now let’s reverse this animation. 👈
open class FadePopAnimator: CustomAnimator {
open func transitionDuration(
utilizing transitionContext: UIViewControllerContextTransitioning?
) -> TimeInterval {
0.5
}
open override func animateTransition(
utilizing transitionContext: UIViewControllerContextTransitioning
) {
guard
let fromViewController = transitionContext.viewController(forKey: .from),
let toViewController = transitionContext.viewController(forKey: .to)
else {
return
}
transitionContext.containerView.insertSubview(toViewController.view, belowSubview: fromViewController.view)
let period = self.transitionDuration(utilizing: transitionContext)
UIView.animate(withDuration: period, animations: {
fromViewController.view.alpha = 0
}, completion: { _ in
transitionContext.completeTransition(
!transitionContext.transitionWasCancelled
)
})
}
}Lastly you simply must implement the navigation controller’s delegate technique as a way to substitute the built-in UIKit system animations. 🛠
extension MainViewController: UINavigationControllerDelegate {
func navigationController(
_ navigationController: UINavigationController,
animationControllerFor operation: UINavigationController.Operation,
from fromVC: UIViewController,
to toVC: UIViewController
) -> UIViewControllerAnimatedTransitioning? {
change operation {
case .push:
return FadePushAnimator()
case .pop:
return FadePopAnimator()
default:
return nil
}
}
}Word that you do not have to make two separate lessons (pop & push), you can too move the operation and implement the animations in a single animated transitioning class.
P.c pushed interactive transitions So, now you know the way to implement a customized transition, however it is time to make it interactive! The method is fairly easy, you may solely want a gesture recognizer and a correct delegate technique to make issues work. ⌨️
class DetailViewController: UIViewController {
var interactionController: UIPercentDrivenInteractiveTransition?
override func viewDidLoad() {
tremendous.viewDidLoad()
self.view.backgroundColor = .lightGray
let edge = UIScreenEdgePanGestureRecognizer(
goal: self,
motion: #selector(self.handleEdgePan(_:))
)
edge.edges = .left
self.view.addGestureRecognizer(edge)
}
override func viewDidAppear(_ animated: Bool) {
tremendous.viewDidAppear(animated)
self.navigationController?.delegate = self
}
@objc func handleEdgePan(_ gesture: UIScreenEdgePanGestureRecognizer) {
let translate = gesture.translation(in: gesture.view)
let p.c = translate.x / gesture.view!.bounds.dimension.width
change gesture.state {
case .started:
self.interactionController = UIPercentDrivenInteractiveTransition()
self.navigationController?.popViewController(animated: true)
case .modified:
self.interactionController?.replace(p.c)
case .ended:
let velocity = gesture.velocity(in: gesture.view)
if p.c > 0.5 || velocity.x > 0 {
self.interactionController?.end()
}
else {
self.interactionController?.cancel()
}
self.interactionController = nil
default:
break
}
}
}
extension DetailViewController: UINavigationControllerDelegate {
func navigationController(
_ navigationController: UINavigationController,
interactionControllerFor animationController: UIViewControllerAnimatedTransitioning
) -> UIViewControllerInteractiveTransitioning? {
interactionController
}
}Contained in the controller that will probably be popped you’ll be able to take possession of the navigation controller’s delegate and implement the interactive transition controller utilizing a left display screen edge pan gesture recognizer. This entire code normally goes into a brand new subclass of UIPercentDrivenInteractiveTransition however for the sake of simplicity this time we’ll skip that, and go along with this very easy resolution. Within the closing instance code you may discover the “subclassed model” of the interactive transition. 😅
Navigation vs modal presentation
Okay, let’s cowl another factor actual fast: customizing modal presentation animations for view controllers. There’s a minor distinction between customizing the navigation stack animations and modal presentation kinds. If you wish to customise a view controller transition you’d normally do one thing like this. 👍
class DetailViewController: UIViewController {
override func put together(for segue: UIStoryboardSegue, sender: Any?) {
tremendous.put together(for: segue, sender: sender)
guard let controller = segue.vacation spot as? ModalViewController else {
return
}
controller.transitioningDelegate = self
controller.modalPresentationStyle = .customized
controller.modalPresentationCapturesStatusBarAppearance = true
}
}
Right here comes the transitioning delegate, utilizing the identical objects that we have already got.
extension DetailViewController: UIViewControllerTransitioningDelegate {
func animationController(forPresented offered: UIViewController,
presenting: UIViewController,
supply: UIViewController) -> UIViewControllerAnimatedTransitioning? {
return FadePushAnimator()
}
func animationController(forDismissed dismissed: UIViewController) -> UIViewControllerAnimatedTransitioning? {
return FadePopAnimator()
}
}In case you run the code and current the modal view controller, that’ll work simply positive. The issue happens whenever you attempt to dismiss the offered view controller. The entire app will flip to a black display screen of loss of life (BSOD). 🖥
(pop != dismiss) && (push != current)
It’s important to modify the pop animation as a way to help modal dismissal animations. Briefly: the issue is with inserting views and reminiscence administration.
open class FadePopAnimator: NSObject, UIViewControllerAnimatedTransitioning {
public enum TransitionType {
case navigation
case modal
}
let kind: TransitionType
let period: TimeInterval
public init(kind: TransitionType, period: TimeInterval = 0.25) {
self.kind = kind
self.period = period
tremendous.init()
}
open func transitionDuration(utilizing transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
return self.period
}
open override func animateTransition(utilizing transitionContext: UIViewControllerContextTransitioning) {
guard
let fromViewController = transitionContext.viewController(forKey: .from)
else {
return
}
if self.kind == .navigation, let toViewController = transitionContext.viewController(forKey: .to) {
transitionContext.containerView.insertSubview(toViewController.view, belowSubview: fromViewController.view)
}
let period = self.transitionDuration(utilizing: transitionContext)
UIView.animate(withDuration: period, animations: {
fromViewController.view.alpha = 0
}, completion: { _ in
transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
})
}
}The most straightforward resolution is to introduce a brand new property so you can also make a call to pop or dismiss the view controller primarily based on that flag. Now you’ll be able to safely use the identical animators for modally offered view controllers as properly. 😬
The pattern code is inside The.Swift.Dev. tutorials repository, you may discover examples for changing the default push & pop navigation animations with customized ones.
Word that the navigation bar will all the time use a fade animation, sadly that may not be custom-made. Additionally I’ve made a customized modal presentation, and the whole lot is utilizing the interactive transitions too. Clearly there may be much more, however under are some hyperlinks that you would be able to comply with in the event you hit an impediment throughout your journey.
Additionally in the event you do not wish to manually implement customized animation results you should use Hero the elegant transition library.