缩放 UIPageControl 的当前点并保持其居中

我对 UIPageControl 进行了子类化，以便使其当前的点更大。

class CustomPageControl: UIPageControl {
    override var currentPage: Int {
        didSet {
            updateDots()
        }
    }

    func updateDots() {
        let currentDot = subviews[currentPage]
        let largeScaling = CGAffineTransform(scaleX: 3, y: 3)

        subviews.forEach {
            // apply the large scale of newly selected dot
            // restore the normal scale of previously selected dot
            $0.transform = $0 == currentDot ? largeScaling : .identity
        }
    }
}

But the result of the transform isn't centered (the red dot should be aligned with the others):

我尝试过（在 iOS 12 上）：

• 改变frame or center of currentDot没有影响。
• 更改转换以包括translatedBy(x: CGFloat, y: CGFloat)没有影响。

• 改变约束条件像这儿正在进行第一个点跳跃：

  currentDot.translatesAutoresizingMaskIntoConstraints = false
  currentDot.centerYAnchor.constraint(equalTo: self.centerYAnchor, constant: 0)
  currentDot.centerXAnchor.constraint(equalTo: self.centerXAnchor, constant: 0)
  

  

我终于通过重写让它工作了all子视图由我自己限制。

// https://stackoverflow.com/a/55063316/1033581
class DefaultPageControl: UIPageControl {

    override var currentPage: Int {
        didSet {
            updateDots()
        }
    }

    override func sendAction(_ action: Selector, to target: Any?, for event: UIEvent?) {
        super.sendAction(action, to: target, for: event)
        updateDots()
    }

    private func updateDots() {
        let currentDot = subviews[currentPage]
        let largeScaling = CGAffineTransform(scaleX: 3.0, y: 3.0)
        let smallScaling = CGAffineTransform(scaleX: 1.0, y: 1.0)

        subviews.forEach {
            // Apply the large scale of newly selected dot.
            // Restore the small scale of previously selected dot.
            $0.transform = $0 == currentDot ? largeScaling : smallScaling
        }
    }

    override func updateConstraints() {
        super.updateConstraints()
        // We rewrite all the constraints
        rewriteConstraints()
    }

    private func rewriteConstraints() {
        let systemDotSize: CGFloat = 7.0
        let systemDotDistance: CGFloat = 16.0

        let halfCount = CGFloat(subviews.count) / 2
        subviews.enumerated().forEach {
            let dot = $0.element
            dot.translatesAutoresizingMaskIntoConstraints = false
            NSLayoutConstraint.deactivate(dot.constraints)
            NSLayoutConstraint.activate([
                dot.widthAnchor.constraint(equalToConstant: systemDotSize),
                dot.heightAnchor.constraint(equalToConstant: systemDotSize),
                dot.centerYAnchor.constraint(equalTo: centerYAnchor, constant: 0),
                dot.centerXAnchor.constraint(equalTo: centerXAnchor, constant: systemDotDistance * (CGFloat($0.offset) - halfCount))
            ])
        }
    }
}

代码中的系统常量（7.0 和 16.0）分别是 iOS 12 上默认 UIPageControl 点的大小和距离。