向 UIScrollView 添加垂直两指滑动手势

根据如何为所有屏幕的 iPhone 应用程序添加垂直滑动手势 https://stackoverflow.com/questions/4640000/how-to-add-a-vertical-swipe-gesture-to-iphone-app-for-all-screens，我添加了两个手指向下滑动的手势window，它在整个应用程序的普通页面上运行良好。但它在页面上失败了UIScrollView（如 UITableViewController）。当我向下滑动时用两个手指 on UIScrollView，它只是像平常一样滚动它。如果我从UINavigationBar上面那个UIScrollView，它又工作正常了。

理想的结果是我可以正常用一根手指滚动tableview，并通过用两根手指滑动页面来调用某些方法而不滚动tableview。这在 TweetBot 中用于切换暗模式，效果完美。

根据苹果公司的文件：使用响应者和响应者链来处理事件 https://developer.apple.com/documentation/uikit/touches_presses_and_gestures/using_responders_and_the_responder_chain_to_handle_events，我想我了解响应者链是如何工作的，所以我想问一下UIScrollView忽略两个手指的滑动手势，以便可以将此事件传递给UIWindow。但我不知道如何：

我尝试实施UIGestureRecognizerDelegate's func gestureRecognizer(_:, shouldRequireFailureOf otherGestureRecognizer:)来自苹果的document https://developer.apple.com/documentation/uikit/touches_presses_and_gestures/coordinating_multiple_gesture_recognizers/preferring_one_gesture_over_another，或覆盖gestureRecognizerShouldBegin(_)通过继承UITableView。但一切都不起作用。

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，如下。

In AppDelegate

// 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
      }
    }
}

And

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

关于与 joern 解决方案的差异的一些解释：

1. Only recognizer.state == .change被关注到。
2. recognizer.translation(in:)的参数应该是window这样我就对特定的风险投资无能为力。
3. 该识别器触发某些方法后，应将其取消，以防止继续触发它们。

没有必要对任何特定的风险投资做任何事情。

这样，两指滑动手势在普通 VC 和滚动 VC 上都可以正常工作。

当您添加UISwipeGestureRecognizer到您的窗口，保留对它的引用，以便您稍后可以通过AppDelegate:

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UIViewController其中包含UITableView (or UIScrollView）你必须打电话require(toFail:)在 UITableView 的平移手势识别器上：

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可以在UITableView.

UPDATE

由于滑动是一种离散手势，因此上述解决方案可能不是完美的解决方案。当您缓慢向下滚动时one用手指你会注意到UITableView不会立即向下滚动。有一个短暂的延迟，因为UITableView's UIPanGestureDelagate必须等到（两根手指）SwipeDelegate 失败。这需要一些时间。

更好的解决方案可能是使用UIPanGestureRecognizer识别两指平移，然后禁用滚动UITableView当用户使用两根手指平移时。

可以这样实现：

在你的 AppDelegate 中：

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
    }
}

在你的视图控制器中：

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

你必须采取UIPanGestureRecognizer来自AppDelegate并将其添加到UITableView。否则这行不通。只需记住将其添加回UIWindow在这之前UIViewController被解雇。

使用此解决方案，正常的滚动行为UITableView保持不变。