检测到 PDFView 确实滚动答案

【问题标题】：Detect that a PDFView did scroll检测到 PDFView 确实滚动
【发布时间】：2018-06-19 11:21:26
【问题描述】：

iOS 上的 PDFKit 是否公开了 PDFView 的底层 UIScrollView，或者有没有其他方法可以直接检测到用户滚动了 PDFView？

我的用例是在文档滚动时隐藏导航栏，作为一种解决方法，我将自己的平移手势识别器添加到 PDFView 的父级，我在gestureRecognizerShouldBegin 中进行隐藏并始终返回false，但我希望有一些东西更像是我在文档中缺少的 UIScrollViewDelegate。

【问题讨论】：

一个 hacky 解决方案：PDFView 有一个继承自 UIScrollView 的 PDFScrollView 子视图（私有类），因此您可以强制转换它并将 UIScrollViewDelegate 设置为它。我做了一个快速设置，它没有设置委托，但你应该检查以防它可能会破坏事情。但是，这些解决方案当然是不安全的，因为 Apple 可能会改变未来的工作方式。

标签： ios cocoa-touch ios-pdfkit

【解决方案1】：

决定了其他人尚未完成的解决方案。对底层UIScrollView 的contentOffset 属性进行键值观察。

您可以使用此扩展程序在每次滚动偏移量更改时运行回调。

var observation = pdfView.onScrollOffsetChanged { scroll in
    print("PDFView scrolled to \(scroll.contentOffset).")
}

扩展

extension PDFView {
    func onScrollOffsetChange(handler: @escaping (UIScrollView) -> Void) -> NSKeyValueObservation? {
        detectScrollView()?.observe(\.contentOffset) { scroll, _ in
            handler(scroll)
        }
    }
    
    private func detectScrollView() -> UIScrollView? {
        for view in subviews {
            if let scroll = view as? UIScrollView {
                return scroll
            } else {
                for subview in view.subviews {
                    if let scroll = subview as? UIScrollView {
                        return scroll
                    }
                }
            }
        }
        
        print("Unable to find a scrollView subview on a PDFView.")
        return nil
    }
}

【讨论】：

【解决方案2】：

iOS 上的 PDFKit 是否公开了 PDFView 的底层 UIScrollView

不，但希望 Apple 将来会添加此功能。记得UIWebView原来没有，后来加的。

或者有没有其他方法可以直接检测到用户滚动了 PDFView

不，PDFViewDelegate 提供的通知似乎都没有解决这个问题。

我正在从 UIWebView 迁移到 PDFView 并且正在使用 scrollViewDidScroll 来处理一堆东西，所以我不想仅仅依靠添加一个平移手势识别器。从@Matthijs 的答案构建，我在 PDFView 中找到 UIScrollView，使我的类成为它的委托，然后将任何事件传递回滚动视图（在我的类成为委托之前它是它自己的委托），以便它可以响应它们，也。使用 UIWebView，这最后一步不是必需的，但使用 PDFView，缩放和可能的其他功能将无法正常工作。

我将覆盖所有记录在案的委托方法，以减少如果 Apple 更改 PDFView 的内部功能而中断的可能性。但是，我必须在每个方法中检查respondsToSelector，因为原始滚动视图委托目前并未实现所有这些。

- (void)viewDidLoad {
    // create the PDFView and find its inner scrollView
    self.pdfView = [[PDFView alloc] init];
    for (UIView *subview in self.pdfView.subviews) {
        if ([subview isKindOfClass:[UIScrollView class]]) {
            self.scrollView = (UIScrollView *)subview;
        } else {
            for (UIView *subsubview in subview.subviews) {
                if ([subsubview isKindOfClass:[UIScrollView class]]) {
                    self.scrollView = (UIScrollView *)subsubview;
                }
            }
        }
    }
}

- (void)loadPDFDocument:(NSString *)URL {
    // load a document, then become the delegate for the scrollView (we have to do that after loading the document)
    PDFDocument *document = [[PDFDocument alloc] initWithURL:URL];
    self.pdfView.document = document;
    self.scrollView.delegate = self;
}

- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
    // *** respond to scroll events here ***

    UIScrollView <UIScrollViewDelegate> *scrollViewDelegate = (UIScrollView <UIScrollViewDelegate> *)self.scrollView;
    if ([scrollViewDelegate respondsToSelector:@selector(scrollViewDidScroll:)]) {
        [scrollViewDelegate scrollViewDidScroll:scrollView];
    }
}

- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView {
    UIScrollView <UIScrollViewDelegate> *scrollViewDelegate = (UIScrollView <UIScrollViewDelegate> *)self.scrollView;
    if ([scrollViewDelegate respondsToSelector:@selector(scrollViewWillBeginDragging:)]) {
        [scrollViewDelegate scrollViewWillBeginDragging:scrollView];
    }
}

- (void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset {
    UIScrollView <UIScrollViewDelegate> *scrollViewDelegate = (UIScrollView <UIScrollViewDelegate> *)self.scrollView;
    if ([scrollViewDelegate respondsToSelector:@selector(scrollViewWillEndDragging:withVelocity:targetContentOffset:)]) {
        [scrollViewDelegate scrollViewWillEndDragging:scrollView withVelocity:velocity targetContentOffset:targetContentOffset];
    }
}

- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate {
    UIScrollView <UIScrollViewDelegate> *scrollViewDelegate = (UIScrollView <UIScrollViewDelegate> *)self.scrollView;
    if ([scrollViewDelegate respondsToSelector:@selector(scrollViewDidEndDragging:willDecelerate:)]) {
        [scrollViewDelegate scrollViewDidEndDragging:scrollView willDecelerate:decelerate];
    }
}

- (BOOL)scrollViewShouldScrollToTop:(UIScrollView *)scrollView {
    UIScrollView <UIScrollViewDelegate> *scrollViewDelegate = (UIScrollView <UIScrollViewDelegate> *)self.scrollView;
    if ([scrollViewDelegate respondsToSelector:@selector(scrollViewShouldScrollToTop:)]) {
        return [scrollViewDelegate scrollViewShouldScrollToTop:scrollView];
    }
    return TRUE;
}

- (void)scrollViewDidScrollToTop:(UIScrollView *)scrollView {
    UIScrollView <UIScrollViewDelegate> *scrollViewDelegate = (UIScrollView <UIScrollViewDelegate> *)self.scrollView;
    if ([scrollViewDelegate respondsToSelector:@selector(scrollViewDidScrollToTop:)]) {
        [scrollViewDelegate scrollViewDidScrollToTop:scrollView];
    }
}

- (void)scrollViewWillBeginDecelerating:(UIScrollView *)scrollView {
    UIScrollView <UIScrollViewDelegate> *scrollViewDelegate = (UIScrollView <UIScrollViewDelegate> *)self.scrollView;
    if ([scrollViewDelegate respondsToSelector:@selector(scrollViewWillBeginDecelerating:)]) {
        [scrollViewDelegate scrollViewWillBeginDecelerating:scrollView];
    }
}

- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView {
    UIScrollView <UIScrollViewDelegate> *scrollViewDelegate = (UIScrollView <UIScrollViewDelegate> *)self.scrollView;
    if ([scrollViewDelegate respondsToSelector:@selector(scrollViewDidEndDecelerating:)]) {
        [scrollViewDelegate scrollViewDidEndDecelerating:scrollView];
    }
}

- (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView {
    UIScrollView <UIScrollViewDelegate> *scrollViewDelegate = (UIScrollView <UIScrollViewDelegate> *)self.scrollView;
    if ([scrollViewDelegate respondsToSelector:@selector(viewForZoomingInScrollView:)]) {
        return [scrollViewDelegate viewForZoomingInScrollView:scrollView];
    }
    return nil;
}

- (void)scrollViewWillBeginZooming:(UIScrollView *)scrollView withView:(UIView *)view {
    UIScrollView <UIScrollViewDelegate> *scrollViewDelegate = (UIScrollView <UIScrollViewDelegate> *)self.scrollView;
    if ([scrollViewDelegate respondsToSelector:@selector(scrollViewWillBeginZooming:withView:)]) {
        [scrollViewDelegate scrollViewWillBeginZooming:scrollView withView:view];
    }
}

- (void)scrollViewDidEndZooming:(UIScrollView *)scrollView withView:(UIView *)view atScale:(CGFloat)scale {
    UIScrollView <UIScrollViewDelegate> *scrollViewDelegate = (UIScrollView <UIScrollViewDelegate> *)self.scrollView;
    if ([scrollViewDelegate respondsToSelector:@selector(scrollViewDidEndZooming:withView:atScale:)]) {
        [scrollViewDelegate scrollViewDidEndZooming:scrollView withView:view atScale:scale];
    }
}

- (void)scrollViewDidZoom:(UIScrollView *)scrollView {
    UIScrollView <UIScrollViewDelegate> *scrollViewDelegate = (UIScrollView <UIScrollViewDelegate> *)self.scrollView;
    if ([scrollViewDelegate respondsToSelector:@selector(scrollViewDidZoom:)]) {
        [scrollViewDelegate scrollViewDidZoom:scrollView];
    }
}

- (void)scrollViewDidEndScrollingAnimation:(UIScrollView *)scrollView {
    UIScrollView <UIScrollViewDelegate> *scrollViewDelegate = (UIScrollView <UIScrollViewDelegate> *)self.scrollView;
    if ([scrollViewDelegate respondsToSelector:@selector(scrollViewDidEndScrollingAnimation:)]) {
        [scrollViewDelegate scrollViewDidEndScrollingAnimation:scrollView];
    }
}

- (void)scrollViewDidChangeAdjustedContentInset:(UIScrollView *)scrollView {
    UIScrollView <UIScrollViewDelegate> *scrollViewDelegate = (UIScrollView <UIScrollViewDelegate> *)self.scrollView;
    if ([scrollViewDelegate respondsToSelector:@selector(scrollViewDidChangeAdjustedContentInset:)]) {
        [scrollViewDelegate scrollViewDidChangeAdjustedContentInset:scrollView];
    }
}

【讨论】：

你能告诉我如何捕捉到何时选择注释。我使用了 PDFViewAnnotationWillHit 通知，但没有运气。
抱歉，我根本没有使用过注释功能。

【解决方案3】：

我这样做是为了检测 pdfView 上的缩放和平移，以将这些手势复制到第二个 pdfView，它在这里工作得非常好。通过我在这里找到的 PanDirectionGestureRecognizer 获得了一些帮助来检测垂直和水平平移：stackoverflow.com/a/55635482/558112

class Document: UIViewController, UIScrollViewDelegate {

    override func viewDidLoad() {
        super.viewDidLoad()

        // Subscribe to notifications.
        NotificationCenter.default.addObserver(self, selector: #selector(onPageZoomAndPan), name: .PDFViewScaleChanged, object: pdfView

        // get the scrollView in pdfView and attach gesture recognizers

        outerLoop: for subView in pdfView.subviews {
            for view in subView.subviews {
                if let scrollView = view as? UIScrollView {
                    let xScrollViewPanGesture = PanDirectionGestureRecognizer(direction: .horizontal, target: self, action: #selector(onPageZoomAndPan))
                    xScrollViewPanGesture.delegate = self
                    scrollView.addGestureRecognizer(xScrollViewPanGesture)

                    let yScrollViewPanGesture = PanDirectionGestureRecognizer(direction: .vertical, target: self, action: #selector(onPageZoomAndPan))
                    yScrollViewPanGesture.delegate = self
                    scrollView.addGestureRecognizer(yScrollViewPanGesture)

                    break outerLoop
                }
            }
        }
    }

    // MARK: - UIScrollViewDelegate

    @objc private func onPageZoomAndPan() {
        let rect = pdfView.convert(pdfView.bounds, to: pdfView.currentPage!)
        pdfViewSecondScreen.scaleFactor = pdfView.scaleFactor
        pdfViewSecondScreen.go(to: rect, on: pdfView.currentPage!)
    }
}



enum PanDirection {
    case vertical
    case horizontal
}


// UIKit.UIGestureRecognizerSubclass

import UIKit.UIGestureRecognizerSubclass

class PanDirectionGestureRecognizer: UIPanGestureRecognizer {

    let direction : PanDirection

    init(direction: PanDirection, target: AnyObject, action: Selector) {
        self.direction = direction
        super.init(target: target, action: action)
    }

    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent) {
        super.touchesMoved(touches, with: event)

        if state == .began {
            let vel = velocity(in: self.view!)

            switch direction {
            case .horizontal where abs(vel.y) > abs(vel.x):
                state = .cancelled
            case .vertical where abs(vel.x) > abs(vel.y):
                state = .cancelled
            default:
                break
            }
        }
    }
}

【讨论】：

当我尝试这个时，UIScrollView 处于子视图的第一级，所以我修改了这段代码来检查每个子视图，然后在需要时检查每个子视图的子视图。

【解决方案4】：

试试这个，

NotificationCenter.default.addObserver(self, selector: #selector(handlePageChange(notification:)), name: Notification.Name.PDFViewPageChanged, object: nil)

@objc private func handlePageChange(notification: Notification)
{
    print("Page changed")
}

【讨论】：

无论情况如何，最好提供一个更通用的解决方案，检查哪个滚动视图发送了通知；我们不知道屏幕上同时有多少滚动视图可能还会发布通知。
我试图获取滚动视图委托以进行 pdfview 滚动，但无法获取。以上解决方案对我有帮助。如果您能够获得 PDFView 的委托，请在此处分享该解决方案。
您不需要代理...通知包含有关发件人的信息。
这个解决方案没有回答这个问题，即确定滚动视图何时发生变化，而不是新页面何时在视图中占主导地位。
@Matthijs，问题 - 他需要在滚动 PDFView 时隐藏导航栏，所以我建议了这个解决方案。如果您在 PDFView 中寻找页码更改，那么您可以在通知功能中使用它 ==> YourPDFView。当前页面。感谢您的评论。