如何使用CrossDissolve幻灯片切换为Tab栏选项卡切换设置动画？

Question

我正在尝试在类似于Facebook应用程序的UITabBarController上创建过渡效果。我设法得到一个“滚动效果”工作Tab键切换，但我似乎无法弄清楚如何交叉溶解（或它至少不起作用）。

这是我目前的代码：

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，那将是很好的，现在已经尝试了几天没有进展......：/

编辑：我通过用以下代码替换UIView.animate块来解决交叉问题：

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，动画真的很滞后，不可用:(

编辑2：对于试图使用这些片段的人，不要忘记为UITabBarController挂钩代表，否则什么都不会发生。

编辑3：我找到了一个完全符合我要求的Swift库：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tabbar委托中添加以下代码：

在Swift 2,3和4上工作

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（4/23/18）由于这个答案越来越受欢迎，我更新了代码以删除强制解包，这是一种不好的做法，并添加了保护声明。

编辑（7/11/18）@AlbertoGarcía是对的。如果您点击两次标签栏图标，则会出现空白屏幕。所以我加了一个额外的支票

Answer 2

如果你想使用UIViewControllerAnimatedTransitioning做一些比UIView.transition更自定义的东西，请看看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
    }
}

Answer 3

要扩展@gmogames的答案：https://stackoverflow.com/a/45362914/1993937

通过代码选择标签栏索引时，我无法将其设置为动画，如调用：

tabBarController.setSeletedIndex(0)

似乎没有通过相同的调用层次结构，它跳过该方法：

tabBarController(_ tabBarController: UITabBarController, shouldSelect viewController: UIViewController)

完全没有动画。

在我的代码中，除了在某些情况下手动设置标签栏项目in-code之外，我还希望为用户点击标签栏项目进行动画转换。

以下是我对上述解决方案的补充，它添加了一种不同的方法来通过代码设置所选索引，该代码将为转换设置动画：

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
    }
}

现在就打电话

tabBarController.setSelectedWithIndex(1)   

用于代码内动画过渡！

我仍然认为不幸的是，要完成这项工作，我们必须覆盖一个不是设置器并操纵其中数据的方法。如果这是我们需要覆盖以完成此操作的方法，它不会使标签栏控制器具有可扩展性。