ios - UIViewControllerAnimatedTransitioning 每隔一段时间才有效？

Question

我已经在这里工作了几个小时，无法理解我做错了什么。我已经按照我之前的 Swift: Problems with custom UIView.transition? 中描述的 UITabBarControllerDelegate 设置了自定义选项卡栏 Controller 转换。

我不使用普通的 Storyboard 标签栏按钮，我以编程方式切换 selectedIndex。我的问题是只有这个实现了:

func tabBarController(_ tabBarController: UITabBarController, animationControllerForTransitionFrom fromVC: UIViewController, to toVC: UIViewController) -> UIViewControllerAnimatedTransitioning? {
        let animator = ModalTransition()
        animator.fromView = fromVC.view
        animator.toView = toVC.view
        return  animator

    }

索引的动画和切换仅每隔一次发生。我有自定义按钮来切换索引，每隔一段时间，单击切换按钮时没有任何反应。这是我的动画:

//
//  ModalTransition.swift
//  Adventures In Design
//
//  Created by Skylar Thomas on 8/28/17.
//

import UIKit

class ModalTransition: NSObject, UIViewControllerAnimatedTransitioning {

    weak var transitionContext: UIViewControllerContextTransitioning?
    var fromView = UIView()
    var toView = UIView()
    var duration = 1.1


    func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
        return 1
    }

    func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {

        let containerView = transitionContext.containerView
        containerView.addSubview(toView)
        containerView.sendSubview(toBack: toView)

        print("ANIMATING")

        UIView.animate(withDuration: duration, delay: 0.0, usingSpringWithDamping: 0.5, initialSpringVelocity: 0.0, options: .curveLinear, animations: {
            self.fromView.center.y += 900

        }, completion: {
            finished in

            //only works every OTHER click
            transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
            self.fromView.center.y -= 900
        })


    }
}

这是什么原因造成的？是不是什么东西

Answer 1

我认为您没有分配 toView 和 FromView。尝试这样的事情

func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {

    let fromViewController = transitionContext.viewController(forKey: UITransitionContextViewControllerKey.from)!
    let toViewController = transitionContext.viewController(forKey: UITransitionContextViewControllerKey.to)!

    let fromView = fromViewController.view
    let toView = toViewController.view
    let container = transitionContext.containerView
    container.addSubview(toView!)

    // Replace your animations here
    toView?.frame = transitionContext.finalFrame(for: toViewController)
    toView?.alpha = 0

    let duration = self.transitionDuration(using: transitionContext)

    UIView.animate(withDuration: duration, delay: 0, options: .curveEaseInOut, animations: {
      toView?.alpha = 1
      fromView?.alpha = 0

    }, completion: { finished in

      toView?.alpha = 1.0
      fromView?.alpha = 1
      fromView?.removeFromSuperview()
      transitionContext.completeTransition(true)
    })
  }