ios - 如何使用 CrossDissolve 幻灯片过渡动画标签栏选项卡切换？

Question

我正在尝试在 UITabBarController 上创建一个过渡效果，有点类似于 Facebook 应用程序。我设法在选项卡开关上获得了“滚动效果”，但我似乎无法弄清楚如何交叉溶解(或者它至少不起作用)。

这是我当前的代码:

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
        })
    }
}

如果有人知道如何让这个工作，那就太好了，现在已经尝试了好几天没有进展......:/

编辑:我通过将 UIView.animate block 替换为:

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

})

但是，动画真的很慢而且不可用:(

编辑 2:对于尝试使用这些片段的人，不要忘记连接 UITabBarController 的委托(delegate)，否则什么也不会发生。

编辑 3: 我找到了一个 Swift 库，它完全符合我的要求: https://github.com/Interactive-Studio/TransitionableTab

Answer 1

有一种更简单的方法可以做到这一点。在标签栏委托(delegate)中添加以下代码:

使用 Swift 2、3 和 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
    }
}

编辑(2018 年 4 月 23 日)由于这个答案越来越受欢迎，我更新了代码以删除强制展开，这是一种不好的做法，并添加了 guard 语句。

编辑(2018 年 7 月 11 日)@AlbertoGarcía 是对的。如果你点击标签栏图标两次，你会得到一个空白屏幕。所以我加了一张额外的支票