如何让UIResponder用ios-chart手指跟踪？

Question

我想在移动设备上使用图表时跟踪手指，因此我使用UIResponder并覆盖touchBegan，touchMoved和touchEnded，如下所示。

var startLocation: CGPoint?
var totalDistance: CGFloat = 0


override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
    super.touchesBegan(touches, with: event)
    if let touch = touches.first {
        totalDistance = 0
        startLocation = touch.location(in: self.chart1)
    }
}

override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
    super.touchesMoved(touches, with: event)
    if let startLocation = startLocation, let touch = touches.first {
        let currentLocation = touch.location(in: self.chart1)
        let dX = currentLocation.x - startLocation.x
        let dY = currentLocation.y - startLocation.y
        self.totalDistance += sqrt(pow(dX, 2) + pow(dY, 2))
        self.startLocation = currentLocation

    }
}

override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
    super.touchesEnded(touches, with: event)
    print("Total distance: \(totalDistance)")
}

我构建了一个名为chart1的视图来呈现图表视图。我可以计算图表1外的空间距离。但是当我在图表上滑动时，我无法计算距离。 有人能给我一些建议吗？ 任何帮助表示赞赏。