在UIScrollView中添加垂直双指滑动手势

Question

根据如何为所有屏幕添加垂直滑动手势到iPhone应用程序的说法，我给window添加了一个双指向下滑动的手势，这在整个应用程序的普通页面上运行得很好。但是它在有UIScrollView的页面上失败了(比如UITableViewController)。当我用两根手指在上滑动时，它只是像往常一样滚动。如果我从UINavigationBar上滑过UIScrollView，它又能正常工作了。

理想的结果是，我可以正常滚动一个手指的表视图，并调用一些方法，用两个手指滑动页面，而不滚动表视图。这是用于TweetBot切换暗模式，工作完美。

根据苹果公司的文件：使用Responders和Responder链处理事件，我想我理解应答器链是如何工作的，所以我想让UIScrollView忽略这两个手指的滑动手势，这样它就可以把这个事件传递给UIWindow。但我想不出如何：

我试着从苹果的UIGestureRecognizerDelegate的文档中实现func gestureRecognizer(_:, shouldRequireFailureOf otherGestureRecognizer:)，或者通过继承UITableView来覆盖gestureRecognizerShouldBegin(_)，但都没有成功。

欢迎任何解决方案或建议。

更新-最终解决方案

我简化了joern的解决方案，下面是。

在AppDelegate中

// It's not necessary to keep a reference to gesture unless you want to do something further.
lazy var gesture: UIPanGestureRecognizer = {
    let gesture = UIPanGestureRecognizer(target: self, action: #selector(twoFingerDidSwipe(recognizer:)))
    gesture.minimumNumberOfTouches = 2
    gesture.maximumNumberOfTouches = 2
    return gesture
}()

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
    gesture.delegate = AppDelegate
    window.addGestureRecognizer(gesture)
    return true
}

@objc func twoFingerDidSwipe(recognizer: UIPanGestureRecognizer) {
    let swipeThreshold: CGFloat = 50

    if recognizer.state == .changed { // 1
      switch recognizer.translation(in: window).y { // 2
      case ...(-swipeThreshold):
        print("Swipe Up")
        recognizer.state = .cancelled // 3
      case swipeThreshold...:
        print("Swipe Down")
        recognizer.state = .cancelled
      default:
        break
      }
    }
}

和

extension AppDelegate: UIGestureRecognizerDelegate {
  func gestureRecognizer(_ gestureRecognizer: UIGestureRecognizer, shouldRecognizeSimultaneouslyWith otherGestureRecognizer: UIGestureRecognizer) -> Bool {
    return true
  }
}

关于与joern解决方案不同之处的一些解释：

1. 唯一关心的是recognizer.state == .change。
2. recognizer.translation(in:)的参数应该是window，这样我就不能对特定的VC做任何事情。
3. 在此识别器触发某些方法后，应取消该方法，以防止其继续触发。

没有必要对任何特定的VC做任何事情。

这样，双指滑动手势在普通VC和滚动VC上都能很好地工作.

Answer 1

将UISwipeGestureRecognizer添加到窗口时，保留对它的引用，以便以后可以通过AppDelegate访问它。

class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?
    var twoFingerSwipeDownRecognizer: UISwipeGestureRecognizer?

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {

        let twoFingerSwipeDownRecognizer = UISwipeGestureRecognizer(target: self, action: #selector(didRecognizeTwoFingerSwipeDown))
        twoFingerSwipeDownRecognizer.numberOfTouchesRequired = 2
        twoFingerSwipeDownRecognizer.direction = .down
        window?.addGestureRecognizer(twoFingerSwipeDownRecognizer)
        self.twoFingerSwipeDownRecognizer = twoFingerSwipeDownRecognizer

        return true
    }

    @objc func didRecognizeTwoFingerSwipeDown(recognizer: UISwipeGestureRecognizer) {
        print("SWIPE DOWN")
    }
}

然后，在包含UITableView (或UIScrollView)的UITableView中，您必须在UITableView的pan手势识别器上调用require(toFail:)：

func enableTwoFingerSlideDown() {
    guard
        let appDelegate = UIApplication.shared.delegate as? AppDelegate,
        let twoFingerGestureRecognizer = appDelegate.twoFingerSwipeDownRecognizer
        else {
            return
        }
    tableView.panGestureRecognizer.require(toFail: twoFingerGestureRecognizer)
}

现在，两根手指向下的手势在UITableView上起作用。

更新

因为滑动是一个离散的手势，上面的解决方案可能不是完美的解决方案。当您用一个手指慢慢向下滚动时，您会注意到UITableView不会立即向下滚动。由于UITableView's UIPanGestureDelagate必须等待(两个手指) SwipeDelegate失败，所以延迟时间很短。这需要一些时间。

更好的解决方案可能是使用UIPanGestureRecognizer识别两个手指盘，然后在用户使用两个手指进行摇摄时禁用UITableView上的滚动。

这是可以做到的：

In your AppDelegate:

class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?
    var twoFingerPanRecognizer: UIPanGestureRecognizer?

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {

        let twoFingerSwipeDownRecognizer = UIPanGestureRecognizer(target: self, action: #selector(didRecognizeTwoFingerPan))
        twoFingerSwipeDownRecognizer.minimumNumberOfTouches = 2
        twoFingerSwipeDownRecognizer.maximumNumberOfTouches = 2
        twoFingerPanRecognizer?.delegate = self
        window?.addGestureRecognizer(twoFingerSwipeDownRecognizer)
        self.twoFingerPanRecognizer = twoFingerSwipeDownRecognizer

        return true
    }

    @objc func didRecognizeTwoFingerPan(recognizer: UIPanGestureRecognizer) {
        let tableView = recognizer.view as? UITableView
        switch recognizer.state {
        case .began:
            tableView?.isScrollEnabled = false
        case .changed:
            let swipeThreshold: CGFloat = 50
            switch recognizer.translation(in: nil).y {
            case ...(-swipeThreshold):
                print("Swipe UP")
                recognizer.isEnabled = false
            case swipeThreshold...:
                print("Swipe DOWN")
                recognizer.isEnabled = false
            default:
                break
            }
        case .cancelled, .ended, .failed, .possible:
            tableView?.isScrollEnabled = true
            recognizer.isEnabled = true
        }
    }
}

extension AppDelegate: UIGestureRecognizerDelegate {
    func gestureRecognizer(_ gestureRecognizer: UIGestureRecognizer, shouldRecognizeSimultaneouslyWith otherGestureRecognizer: UIGestureRecognizer) -> Bool {
        return true
    }
}

In your ViewController:

func enableTwoFingerSlideDown() {
        guard
            let appDelegate = UIApplication.shared.delegate as? AppDelegate,
            let twoFingerGestureRecognizer = appDelegate.twoFingerPanRecognizer
            else {
                return
            }
        tableView.addGestureRecognizer(twoFingerGestureRecognizer)
    }

您必须从UIPanGestureRecognizer中获取AppDelegate并将其添加到UITableView中。否则这就行不通了。请记住，在此UIWindow被取消之前，请将其添加回UIViewController。

使用此解决方案，UITableView的正常滚动行为保持不变。