问题
I'm trying to create a transition effect on a UITabBarController somewhat similar to the Facebook app. I managed to get a "scrolling effect" working on tab switch, but I can't seem to figure out how to cross dissolve (or it doesn't work at least).
Here's my current code:
import UIKit
class ScrollingTabBarControllerDelegate: NSObject, UITabBarControllerDelegate {
func tabBarController(_ tabBarController: UITabBarController, animationControllerForTransitionFrom fromVC: UIViewController, to toVC: UIViewController) -> UIViewControllerAnimatedTransitioning? {
return ScrollingTransitionAnimator(tabBarController: tabBarController, lastIndex: tabBarController.selectedIndex)
}
}
class ScrollingTransitionAnimator: NSObject, UIViewControllerAnimatedTransitioning {
weak var transitionContext: UIViewControllerContextTransitioning?
var tabBarController: UITabBarController!
var lastIndex = 0
func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
return 0.2
}
init(tabBarController: UITabBarController, lastIndex: Int) {
self.tabBarController = tabBarController
self.lastIndex = lastIndex
}
func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
self.transitionContext = transitionContext
let containerView = transitionContext.containerView
let fromViewController = transitionContext.viewController(forKey: UITransitionContextViewControllerKey.from)
let toViewController = transitionContext.viewController(forKey: UITransitionContextViewControllerKey.to)
containerView.addSubview(toViewController!.view)
var viewWidth = toViewController!.view.bounds.width
if tabBarController.selectedIndex < lastIndex {
viewWidth = -viewWidth
}
toViewController!.view.transform = CGAffineTransform(translationX: viewWidth, y: 0)
UIView.animate(withDuration: self.transitionDuration(using: (self.transitionContext)), delay: 0.0, usingSpringWithDamping: 1.2, initialSpringVelocity: 2.5, options: .transitionCrossDissolve, animations: {
toViewController!.view.transform = CGAffineTransform.identity
fromViewController!.view.transform = CGAffineTransform(translationX: -viewWidth, y: 0)
}, completion: { _ in
self.transitionContext?.completeTransition(!self.transitionContext!.transitionWasCancelled)
fromViewController!.view.transform = CGAffineTransform.identity
})
}
}
Would be great if anyone know how to get this to work, been trying for days now without progress... :/
edit: I got a cross dissolve working by replacing the UIView.animate block with:
UIView.transition(with: containerView, duration: 0.2, options: .transitionCrossDissolve, animations: {
toViewController!.view.transform = CGAffineTransform.identity
fromViewController!.view.transform = CGAffineTransform(translationX: -viewWidth, y: 0)
}, completion: { _ in
self.transitionContext?.completeTransition(!self.transitionContext!.transitionWasCancelled)
fromViewController!.view.transform = CGAffineTransform.identity
})
However, the animation is really laggy and not usable :(
edit 2: For people trying to use these snippets, don't forget to hook up the delegate for the UITabBarController, otherwise nothing will happen.
edit 3: I've found a Swift library that does exactly what I was looking for: https://github.com/Interactive-Studio/TransitionableTab
回答1:
There is a simpler way to doing this. Add the following code in the tabbar delegate:
Working on Swift 2, 3 and 4
class MySubclassedTabBarController: UITabBarController {
override func viewDidLoad() {
super.viewDidLoad()
delegate = self
}
}
extension MySubclassedTabBarController: UITabBarControllerDelegate {
func tabBarController(_ tabBarController: UITabBarController, shouldSelect viewController: UIViewController) -> Bool {
guard let fromView = selectedViewController?.view, let toView = viewController.view else {
return false // Make sure you want this as false
}
if fromView != toView {
UIView.transition(from: fromView, to: toView, duration: 0.3, options: [.transitionCrossDissolve], completion: nil)
}
return true
}
}
EDIT (4/23/18) Since this answer is getting popular, I updated the code to remove the force unwraps, which is a bad practice, and added the guard statement.
EDIT (7/11/18) @AlbertoGarcía is right. If you tap the tabbar icon twice you get a blank screen. So I added an extra check
回答2:
If you want to use UIViewControllerAnimatedTransitioning to do something more custom than UIView.transition, take a look at this gist.
// MyTabController.swift
import UIKit
class MyTabBarController: UITabBarController {
override func viewDidLoad() {
super.viewDidLoad()
delegate = self
}
}
extension MyTabBarController: UITabBarControllerDelegate {
func tabBarController(_ tabBarController: UITabBarController, animationControllerForTransitionFrom fromVC: UIViewController, to toVC: UIViewController) -> UIViewControllerAnimatedTransitioning? {
return MyTransition(viewControllers: tabBarController.viewControllers)
}
}
class MyTransition: NSObject, UIViewControllerAnimatedTransitioning {
let viewControllers: [UIViewController]?
let transitionDuration: Double = 1
init(viewControllers: [UIViewController]?) {
self.viewControllers = viewControllers
}
func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
return TimeInterval(transitionDuration)
}
func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
guard
let fromVC = transitionContext.viewController(forKey: UITransitionContextViewControllerKey.from),
let fromView = fromVC.view,
let fromIndex = getIndex(forViewController: fromVC),
let toVC = transitionContext.viewController(forKey: UITransitionContextViewControllerKey.to),
let toView = toVC.view,
let toIndex = getIndex(forViewController: toVC)
else {
transitionContext.completeTransition(false)
return
}
let frame = transitionContext.initialFrame(for: fromVC)
var fromFrameEnd = frame
var toFrameStart = frame
fromFrameEnd.origin.x = toIndex > fromIndex ? frame.origin.x - frame.width : frame.origin.x + frame.width
toFrameStart.origin.x = toIndex > fromIndex ? frame.origin.x + frame.width : frame.origin.x - frame.width
toView.frame = toFrameStart
DispatchQueue.main.async {
transitionContext.containerView.addSubview(toView)
UIView.animate(withDuration: self.transitionDuration, animations: {
fromView.frame = fromFrameEnd
toView.frame = frame
}, completion: {success in
fromView.removeFromSuperview()
transitionContext.completeTransition(success)
})
}
}
func getIndex(forViewController vc: UIViewController) -> Int? {
guard let vcs = self.viewControllers else { return nil }
for (index, thisVC) in vcs.enumerated() {
if thisVC == vc { return index }
}
return nil
}
}
回答3:
To expand on @gmogames answer: https://stackoverflow.com/a/45362914/1993937
I couldn't get this to animate when selecting the tab bar index via code, as calling:
tabBarController.setSeletedIndex(0)
Doesn't seem to go through the same call heirarchy, and it skips the method:
tabBarController(_ tabBarController: UITabBarController, shouldSelect viewController: UIViewController)
entirely, resulting in no animation.
In my code I wanted to have an animation transition for a user tapping a tab bar item in addition to me setting the tab bar item in-code manually under certain circumstances.
Here is my addition to the solution above which adds a different method to set the selected index via code that will animate the transition:
import Foundation
import UIKit
@objc class CustomTabBarController: UITabBarController {
override func viewDidLoad() {
super.viewDidLoad()
delegate = self
}
@objc func set(selectedIndex index : Int) {
_ = self.tabBarController(self, shouldSelect: self.viewControllers![index])
}
}
@objc extension CustomTabBarController: UITabBarControllerDelegate {
@objc func tabBarController(_ tabBarController: UITabBarController, shouldSelect viewController: UIViewController) -> Bool {
guard let fromView = selectedViewController?.view, let toView = viewController.view else {
return false // Make sure you want this as false
}
if fromView != toView {
UIView.transition(from: fromView, to: toView, duration: 0.3, options: [.transitionCrossDissolve], completion: { (true) in
})
self.selectedViewController = viewController
}
return true
}
}
Now just call
tabBarController.setSelectedWithIndex(1)
for an in-code animated transition!
I still think it is unfortunate that to get this done we have to override a method that isn't a setter and manipulate data within it. It doesn't make the tab bar controller as extensible as it should be if this is the method that we need to override to get this done.
来源：https://stackoverflow.com/questions/44346280/how-to-animate-tab-bar-tab-switch-with-a-crossdissolve-slide-transition