ios - 在 UIPageViewController 中获取用户滑动方向

Question

UIPageViewControllerDataSource 的这两个方法 viewControllerBeforeViewController 和 viewControllerAfterViewController 不会告诉滑动的方向。

UIPageViewController 委托(delegate)的方法transitionCompleted 也帮不了我们太多。它只是告诉页面是否被完全滑动。

那么我应该使用什么方法来准确检测用户方向(左或右)？

可能这两个属性可能会有所帮助:

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

我的代码是这样的:

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所说的，

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(delegate)方法来确定过渡是向前还是向后。在类的开头声明几个索引变量，例如 currentIndex 和 nextIndex(均为 Int)。

在 willTransitionToViewControllers 方法中，将 nextIndex 设置为挂起 View Controller 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

此时您可以确定转换是向前还是向后: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 View Controller 的转换)，设置 currentIndex 等于 nextIndex 这样您就可以在任何需要指示屏幕上当前显示哪个页面的地方使用 currentIndex:

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