如何解决PDFView和SCrollView [Swift5，iOS 14]之间的手势冲突

Question

我正在为iPads创建一个PDF查看器，用户可以通过滚动水平来读取PDF。

我创建了下面的代码来实现带有手势的页面更改(同时咨询How to create a single page vertical scrolling PDFView in Swift和其他地方)的单一页面视图。

虽然这种方法在大多数情况下都能很好地工作，但我意识到当PDF文件被放大时，没有检测到(或调用)手势。因此，我不能通过滑动屏幕进入下一页。使用我创建的extension PDFView {}函数，我发现禁用subview中的用户交互使我能够检测到滑动手势。但是，现在我不能在PDFView中滚动页面。如果你能帮我解决这个问题，我会很感激的。

我想要实现的是类似于‎PDF Expert (https://apps.apple.com/us/app/pdf-expert-pdf-reader-editor/id743974925)的东西，在这里我可以水平滚动到下一页。

非常感谢您的帮助，提前！

import UIKit
import PDFKit

//PDF Zoom scale
var scaleOfPdf: CGFloat = 4

extension PDFView {
    func disableBouncing(){
        for subview in subviews{
            if let scrollView = subview as? UIScrollView{
                scrollView.bounces = false
                return
            }
}

class ViewController: UIViewController, UIGestureRecognizerDelegate,  UIDocumentPickerDelegate {

    @IBOutlet weak var pdfView: PDFView!
    
    override func viewDidLoad(){
        super.viewDidLoad()


            pdfView.autoresizesSubviews = true
            pdfView.autoresizingMask = [.flexibleWidth, .flexibleHeight, .flexibleTopMargin, .flexibleLeftMargin]
            
            pdfView.displayDirection = .horizontal
            pdfView.displayMode = .singlePage
            pdfView.autoScales = true
            // setting a color for background
            pdfView.backgroundColor = .black
            pdfView.document = pdfDocument
            //            pdfView.usePageViewController(true, withViewOptions: [UIPageViewController.OptionsKey.interPageSpacing: 20])
            pdfView.maxScaleFactor = 4.0
            pdfView.minScaleFactor = pdfView.scaleFactorForSizeToFit
            
            pdfView.disableBouncing()  


       //setting swipe gesture
        let leftSwipeGesture = UISwipeGestureRecognizer(target: self, action: #selector(respondLeftSwipeGesture(_:)))
        leftSwipeGesture.direction = [UISwipeGestureRecognizer.Direction.left]
        pdfView.addGestureRecognizer(leftSwipeGesture)
        
        let rightSwipeGesture = UISwipeGestureRecognizer(target: self, action: #selector(respondRightSwipeGesture(_:)))
        rightSwipeGesture.direction = [UISwipeGestureRecognizer.Direction.right]
        pdfView.addGestureRecognizer(rightSwipeGesture)

    }
    
        
    //setting swipe-gesture
    @objc func respondLeftSwipeGesture(_ sender: UISwipeGestureRecognizer) {
        print("left swipe was detected")
        if pdfView.document == nil { return }
        scaleOfPdf = pdfView.scaleFactor
        pdfView.goToNextPage(self)
        pdfView.scaleFactor = scaleOfPdf
    }
    
    @objc func respondRightSwipeGesture(_ sender: UISwipeGestureRecognizer) {
        print("right swipe was detected")
        if pdfView.document == nil { return }
        scaleOfPdf = pdfView.scaleFactor
        pdfView.goToPreviousPage(self)
        pdfView.scaleFactor = scaleOfPdf
    }
}

Answer 1

手势识别器是一个链式或流水线，处理触摸-在一个(G1)失败后，第二个(G2)试图识别它的手势。这里至少有4个识别器--你的2个(left和right)和2个滚动视图(pan和pinch)。我将给出一个简单的解决方案，它只涵盖滚动视图的pan识别器，如果您也会看到pinch的问题--您将需要遵循相同的方法。

假设G1是您的left识别器，G2是滚动视图的pan识别器。为了使G2过程与G1过程相同，应该要求它们同时识别。

此外，用户在垂直滚动时可能会水平移动手指，因此在这种情况下，您还希望只有在G1放弃滑动而无法识别时才开始滚动。

为了实现这一点，您应该将此代码添加到您的VC中。

override func viewDidLoad(){
    super.viewDidLoad()
    
    ...
    
    leftSwipeGesture.delegate = self
    leftSwipeGesture.cancelsTouchesInView = false
    rightSwipeGesture.delegate = self
    rightSwipeGesture.cancelsTouchesInView = false
}

optional func gestureRecognizer(_ gestureRecognizer: UIGestureRecognizer, 
                                shouldRecognizeSimultaneouslyWith otherGestureRecognizer: UIGestureRecognizer) -> Bool {
    return gestureRecognizer == leftSwipeGesture
        || gestureRecognizer == rightSwipeGesture
        || otherGestureRecognizer == leftSwipeGesture
        || otherGestureRecognizer == rightSwipeGesture
}

optional func gestureRecognizer(_ gestureRecognizer: UIGestureRecognizer, 
                                shouldRequireFailureOf otherGestureRecognizer: UIGestureRecognizer) -> Bool {
    guard let _ = gestureRecognizer as? UIPanGestureRecognizer else { return false }
    return otherGestureRecognizer == leftSwipeGesture
        || otherGestureRecognizer == rightSwipeGesture
}

optional func gestureRecognizer(_ gestureRecognizer: UIGestureRecognizer, 
                                shouldBeRequiredToFailBy otherGestureRecognizer: UIGestureRecognizer) -> Bool {
    guard let _ = otherGestureRecognizer as? UIPanGestureRecognizer else { return false }
    return gestureRecognizer == leftSwipeGesture
        || gestureRecognizer == rightSwipeGesture
}

如果我添加的UIGestureRecognizerDelegate方法没有被调用，您将需要创建一个子类PDFView，使left/rightSwipeGesture.delegate = pdfView并在您的PDFView子类中使用这个逻辑覆盖它的UIGestureRecognizerDelegate方法。