具有延迟TouchesBegan 的手势识别器停止所有对touchesMoved 的调用？

Question

下面的视图控制器代码演示了我的问题。它会打印一些调试语句以响应触摸事件和捏合手势。

如果手势识别器被禁用，并且我在屏幕上拖动手指，一切都会按预期进行：控制器会得到一个touchesBegan、一堆touchesMoved 和一个touchesEnded。但是，如果我启用手势识别器并将其delaysTouchesBegan 属性设置为true，并拖动一个手指，控制器将只接收touchesBegan 和touchesEnded 调用——没有touchesMoved。

delaysTouchesBegan 的文档建议触摸事件会在手势识别器失败后堆积并传递。这是预期的行为 - 丢失所有 touchesMoved 事件吗？

class ViewController: UIViewController {

    var gr: UIPinchGestureRecognizer!

    override func viewDidLoad() {
        super.viewDidLoad()
        gr = UIPinchGestureRecognizer(target: self, action: #selector(pinched(_:)))
        gr.delaysTouchesBegan = true
        view.addGestureRecognizer(gr)
    }

    @IBAction func buttonTapped(_ sender: Any) {
        gr.isEnabled = !gr.isEnabled
        print("pinch recognizer enabled: \(gr.isEnabled)")
    }

    @objc func pinched(_ gr: Any?) {
        print("pinched")
    }

    var i = 0

    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        i = 0
        print("touchesBegan")
    }

    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
        print("touchesMoved \(i)")
        i += 1
    }

    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
        print("touchesEnded")
    }

    override func touchesCancelled(_ touches: Set<UITouch>, with event: UIEvent?) {
        print("touchesCancelled")
    }
}

Answer 1

每次手指之间的距离发生变化时，捏合手势识别器都会报告变化。手指之间的距离被报告为比例因子。因此，您需要查看比例因子，而不是 touchesMoved。这有帮助吗？

@objc func pinched(_ gr: UIPinchGestureRecognizer) {

    if gr.state == .began  {
        print("began")
    }

    if gr.state == .changed {
        print("scale: \(gr.scale)")
    }

    if gr.state == .ended {
        print("ended")
    }
}

Handling Pinch Gestures

Handling Pinch Gestures ( Swift 4 - 2018 )