UIKit customized transition API – a theoretical lesson
There are various lessons and delegates concerned in the course of the course of of creating a customized transition, let’s stroll by means of this stuff actual fast, and do some coding afterwards.
UIViewControllerTransitioningDelegate
Each view controller can have a transition delegate, in that delegate implementation you may present the customized animation and interplay controllers. These objects shall be liable for the precise animation course of, and this delegate is the place the place you may “inject your code” to the UIKit framework. 💉
UINavigationControllerDelegate
The navigation controller delegate additionally has two strategies which can be liable for customized push and pop animations. It is nearly the identical because the transitioning delegate for the view controllers, however you will see this in motion afterward. 💥
UINavigationController.Operation
The navigation controller operation is simply an enum which incorporates the “path” of the navigation animation. Normally push or pop.
Presenting and dismissing one thing modally is just not 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 mainly that is the place the place you implement the flamboyant customized view animations. 😉
UIViewControllerContextTransitioning
This context encapsulates all the data concerning the transitioning, you will get the collaborating views, controllers and lots of extra from this object. The transitioning context is accessible 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 capacity to swipe a navigation controller interactively again (and forth in case 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 how you can make a primary 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 length = self.transitionDuration(utilizing: transitionContext)
UIView.animate(withDuration: length, animations: {
toViewController.view.alpha = 1
}, completion: { _ in
transitionContext.completeTransition(
!transitionContext.transitionWasCancelled
)
})
}
}As you may see making a customized transition animation is actually easy. You simply should implement two delegate strategies. One among them will return the length of the animation, and the opposite will include the precise transition.
The transition context supplies a customized containterView object that you need to use within the animation, additionally you may seize the collaborating 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 length = self.transitionDuration(utilizing: transitionContext)
UIView.animate(withDuration: length, animations: {
fromViewController.view.alpha = 0
}, completion: { _ in
transitionContext.completeTransition(
!transitionContext.transitionWasCancelled
)
})
}
}Lastly you simply should implement the navigation controller’s delegate methodology in an effort to change 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
}
}
}Notice that you do not have to make two separate lessons (pop & push), it’s also possible to go the operation and implement the animations in a single animated transitioning class.
% 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 will solely want a gesture recognizer and a correct delegate methodology 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.measurement.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 shall be popped you may take possession of the navigation controller’s delegate and implement the interactive transition controller utilizing a left display screen edge pan gesture recognizer. This complete 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 ultimate instance code you will discover the “subclassed model” of the interactive transition. 😅
Navigation vs modal presentation
Okay, let’s cowl yet one more 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 the event you run the code and current the modal view controller, that’ll work simply effective. The issue happens if you attempt to dismiss the offered view controller. The entire app will flip to a black display screen of demise (BSOD). 🖥
(pop != dismiss) && (push != current)
You must modify the pop animation in an effort to assist modal dismissal animations. In brief: the issue is with putting views and reminiscence administration.
open class FadePopAnimator: NSObject, UIViewControllerAnimatedTransitioning {
public enum TransitionType {
case navigation
case modal
}
let sort: TransitionType
let length: TimeInterval
public init(sort: TransitionType, length: TimeInterval = 0.25) {
self.sort = sort
self.length = length
tremendous.init()
}
open func transitionDuration(utilizing transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
return self.length
}
open override func animateTransition(utilizing transitionContext: UIViewControllerContextTransitioning) {
guard
let fromViewController = transitionContext.viewController(forKey: .from)
else {
return
}
if self.sort == .navigation, let toViewController = transitionContext.viewController(forKey: .to) {
transitionContext.containerView.insertSubview(toViewController.view, belowSubview: fromViewController.view)
}
let length = self.transitionDuration(utilizing: transitionContext)
UIView.animate(withDuration: length, animations: {
fromViewController.view.alpha = 0
}, completion: { _ in
transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
})
}
}The simplest resolution is to introduce a brand new property so you can also make a call to pop or dismiss the view controller based mostly on that flag. Now you may safely use the identical animators for modally offered view controllers as nicely. 😬
The pattern code is inside The.Swift.Dev. tutorials repository, you will discover examples for changing the default push & pop navigation animations with customized ones.
Notice that the navigation bar will all the time use a fade animation, sadly that may not be personalized. Additionally I’ve made a customized modal presentation, and the whole lot is utilizing the interactive transitions too. Clearly there’s much more, however under are some hyperlinks that you could comply with in case you hit an impediment throughout your journey.
Additionally in case you do not wish to manually implement customized animation results you need to use Hero the elegant transition library.
