在 UIPageViewController 中获取用户滑动方向

Question

UIPageViewControllerDataSource 的 viewControllerBeforeViewController 和 viewControllerAfterViewController 这两个方法不知道滑动的方向。

UIPageViewController 委托的方法transitionCompleted 也对我们没有多大帮助。它只是告诉页面是否被完全刷过。

那么我应该使用什么方法来准确检测用户方向（左或右）？

这两个属性可能会有所帮助：

let directionForward = UIPageViewControllerNavigationDirection.Forward
let directionReverse = UIPageViewControllerNavigationDirection.Reverse

我的代码如下所示：

import UIKit

class ProView: UIViewController, UIPageViewControllerDataSource, UIPageViewControllerDelegate {

var pageViewController: UIPageViewController?

let characterImages = ["character1", "character2", "character1", "character2", "character1", "character2", "character1", "character2"]

override func viewDidLoad() {
    super.viewDidLoad()
    createPageViewController()
    setupPageControl()

    character = 1
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
}

// Forward, check if this IS NOT the last controller
func pageViewController(pageViewController: UIPageViewController,
    viewControllerAfterViewController ProView: UIViewController) -> UIViewController? {

        let itemController = ProView as PageItemController

        // Check if there is another view
        if itemController.itemIndex+1 < characterImages.count {

            return getItemController(itemController.itemIndex+1)
        }

        return nil
}


// Check if this IS NOT the first controller
func pageViewController(pageViewController: UIPageViewController,
    viewControllerBeforeViewController ProView: UIViewController) -> UIViewController? {

    let itemController = ProView as PageItemController

        if itemController.itemIndex < 0 {

            return getItemController(itemController.itemIndex-1)
        }

        return nil
}

private func getItemController(itemIndex: Int) -> PageItemController? {

    if itemIndex < characterImages.count {
        let pageItemController = self.storyboard!.instantiateViewControllerWithIdentifier("ItemController") as PageItemController
        pageItemController.itemIndex = itemIndex
        pageItemController.imageName = characterImages[itemIndex]
        return pageItemController
}

    return nil
}

func createPageViewController() {

    let pageController = self.storyboard!.instantiateViewControllerWithIdentifier("PageController") as UIPageViewController
    pageController.dataSource = self
    pageController.delegate = self

    if characterImages.count > 0 {
        let firstController = getItemController(0)!
        let startingViewControllers: NSArray = [firstController]
        pageController.setViewControllers(startingViewControllers, direction: UIPageViewControllerNavigationDirection.Forward, animated: false, completion: nil)
    }

    pageViewController = pageController
    addChildViewController(pageViewController!)
    self.view.addSubview(pageViewController!.view)
    pageViewController?.didMoveToParentViewController(self)
}

func setupPageControl() {
    let appearance = UIPageControl.appearance()
    appearance.pageIndicatorTintColor = UIColor.grayColor()
    appearance.currentPageIndicatorTintColor = UIColor.whiteColor()
}

func presentationCountForPageViewController(pageViewController: UIPageViewController) -> Int {
    return characterImages.count
}

func presentationIndexForPageViewController(pageViewController: UIPageViewController) -> Int {


}

// BETA

func pageViewController(PageItemController: UIPageViewController,
    didFinishAnimating finished: Bool,
    previousViewControllers pageViewController: [AnyObject],
    transitionCompleted completed: Bool)
{

    if (!completed)
    {
        // You do nothing because whatever page you thought
        // the book was on before the gesture started is still the correct page
        return;
    }

    // This is where you would know the page number changed and handle it appropriately

    character = workaround

    }


}

class PageItemController: UIViewController {

@IBOutlet weak var imageCharacterChoose: UIImageView!

var itemIndex: Int = 0
var imageName: String = "" {
    didSet {

        if let imageView = imageCharacterChoose {imageCharacterChoose.image = UIImage(named: imageName)
        }

    }
}
}

根据pbasdf所说，

var currentIndex: Int = 0
var nextIndex: Int = 0

func pageViewController(PageItemController: UIPageViewController,
    willTransitionToViewControllers pageViewController: [AnyObject]) {

        //                          pageViewController is the pending View Controller
        nextIndex = currentIndex

        // pageViewController...... how do I get its index?
}

Answer 1

您应该同时使用willTransitionToViewControllers: 和didFinishAnimating: 委托方法来确定过渡是向前还是向后。在你的课程开始时声明几个索引变量，比如currentIndex 和nextIndex（都是Int）。

在willTransitionToViewControllers方法中，设置nextIndex等于待处理视图控制器的itemIndex：

编辑

func pageViewController(pageViewController: UIPageViewController, willTransitionToViewControllers pendingViewControllers: [AnyObject]) {
    // the page view controller is about to transition to a new page, so take note
    // of the index of the page it will display.  (We can't update our currentIndex
    // yet, because the transition might not be completed - we will check in didFinishAnimating:)
    if let itemController = pendingViewControllers[0] as? PageItemController {
        nextIndex = itemController.itemIndex
    }
}

结束编辑

此时您可以计算出是向前还是向后过渡：如果nextIndex > currentIndex，则向前；如果 nextIndex currentIndex 则向后。然后在didFinishAnimating 中，如果completed 为真（所以它完成了到下一个视图控制器的转换），将currentIndex 设置为等于nextIndex，这样您就可以在需要指示当前哪个页面的任何地方使用currentIndex在屏幕上：

编辑

func pageViewController(pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [AnyObject], transitionCompleted completed: Bool) {
    if (completed) {
        // the page view controller has successfully transitioned to the next view
        // controller, so we can update our currentIndex to the value we obtained 
        // in the willTransitionToViewControllers method:
        currentIndex = nextIndex

    }
}

请注意，这些方法的第一个参数是 pageViewController（UIPageViewController 的实例），而不是您当前代码中的 pageItemController。

最后，请注意：您引用的枚举 (UIPageViewControllerNavigationDirection) 仅在 setViewControllers(_, direction:) 方法中使用。

结束编辑

Answer 2

就我而言，我只能使用func pageViewController(pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [AnyObject], transitionCompleted completed: Bool) 来确定滑动方向。

这里是如何。假设您已经有一种方法可以引用名为currentIndex 的当前索引。在上面的方法中，你已经有了previousViewControllers的信息，这样你就可以得到之前名为previousIndex的索引。

基本上，这是委托方法内部的实现：

func pageViewController(pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [AnyObject], transitionCompleted completed: Bool) {
  if completed {
    if previousIndex < currentIndex {   // forward

    }
    else if previousIndex > currentIndex {  // reverse

    }
  }
}

Answer 3

假设你有一个 ViewControllers 的本地数组，你可以使用这个delegate 方法：

func pageViewController(_ pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [UIViewController], transitionCompleted completed: Bool) {
    guard let current = self.viewControllers?.first else {
        // TODO handle error
        return
    }

    guard let index = self.pages.firstIndex(of: current) else {
        // TODO handle error
        return
    }

    self.currentIndex = index
}

guard 语句不应失败，但以防万一......

Answer 4

首先在您的 viewControllerForIndex 方法中分配 viewcontroller.view.tag = index 以便每个 viewcontroller.view 都有一个分配的值

有一个 currentIndex 属性，该属性最初分配给您在 pageviewcontroller 中实例化的 viewcontroller 的索引

现在在 didFinishAnimating 中执行以下操作

func pageViewController(_ pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [UIViewController], transitionCompleted completed: Bool) {
        if !completed {
            return     // return if animation is not completed
        }
       let pCont = bottomDataContainer?.viewControllers?[0] as? CustomVC   //take 
       out current VC

        if currentIndex < pCont?.view.tag ?? 0 {
            topNavView.goToNextDate()
        }else{
            topNavView.goToPrevDate()
        }
        selectedIndex = pCont?.view.tag ?? 0
    }

Answer 5

你可以通过实现UIScrollViewDelegate：

var lastScrollDirection: UIPageViewController.NavigationDirection?

func scrollViewWillBeginDragging(_ scrollView: UIScrollView) {
  let translation = scrollView.panGestureRecognizer.translation(in: scrollView.superview)
    
  self.lastScrollDirection = translation.x < 0 ? .forward : .reverse
}

分配委托可能比较棘手。这是我在一个项目中使用的：

func assignScrollDelegate(rootView: UIView) {
  for view in rootView.subviews {
    if let scrollView = view as? UIScrollView {
      scrollView.delegate = self
    }
    else {
      assignScrollDelegate(rootView: view)
    }
  }
}

当您有对UIPageViewController 的引用时调用它。例如，当您的控制器加载时：

override func viewDidLoad() {
  self.assignScrollDelegate(rootView: self.pageController.view)
}

Answer 6

无法确定用户是向前还是向后滑动。

你需要使用这两种方法来提供前后的视图：

pageViewController:viewControllerBeforeViewController:

pageViewController:viewControllerAfterViewController:

您可以通过向 viewControllers 添加属性来跟踪索引，然后您可以比较 pageIndexes。