自定义UIGestureRecognizer失败后，UIPinchGestureRecognizer不会触发

Question

我有一个自定义的UIGestureRecognizer子类，可以检测特定类型的单指拖动。在同一个场景中，我还有一个UIPinchGestureRecognizer，可以检测到双指捏。

问题发生在用户进行捏合手势但是在另一个手指之前瞬间放下一根手指时：自定义手势识别器看到一次触摸并且接合（将其状态设置为.began）而捏合识别器不会。添加第二次触摸后，自定义识别器会注意到并将其状态切换为.failed。但是为时已晚，捏手势识别器无法捡起它。

这是自定义UIGestureRecognizer子类的代码：

override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent) {
    super.touchesBegan(touches, with: event)
    guard touches.count == 1 else {
        state = .failed
        return
    }
    state = .began
}
override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent) {
    super.touchesMoved(touches, with: event)
    guard touches.count == 1 else {
        state = .failed
        return
    }
    // do gesture recognizer stuff here
}

override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent) {
    super.touchesEnded(touches, with: event)
    state = .ended
}

我已经尝试将cancelsTouchesInView设置为false并将delaysTouchesBegan设置为true用于自定义手势识别器。这两种行为都没有区别。

当我使用带有UIPinchGestureRecognizer的UIPanGestureRecognizer时，我没有这个问题，这让我觉得这不是预期的行为。

我的UIGestureRecognizer失败代码有什么问题，我该如何修复它，以便UIPinchGestureRecognizer仍能识别触摸非同时启动的位置？

Answer 1

尝试使用UIGestureRecognizerDelegate协议来实现gestureRecognizer(_:shouldRecognizeSimultaneouslyWith:)。这可以让您同时识别两个手势。

class MyVC: UITableViewController, UIGestureRecognizerDelegate {

    override func viewDidLoad() {
        let pinchGestureRecognizer = UIPinchGestureRecognizer(target: self, action: #selector(handlePinchFrom))
        pinchGestureRecognizer.delegate = self
        view.addGestureRecognizer(pinchGestureRecognizer)
    }

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