snapping/stepping 如何防止 UISlider 跳到位

Question

我有一个可以卡入 5 个不同位置的 UISlider。

slider.minimumValue = 1
slider.maximumValue = 5

卡扣工作正常，但它很突然，无法顺利卡入到位。它有点 "jumps" 到位

我试过设置滚动动画（没用）：

@objc func onSliderValChanged(_ sender: UISlider) {
    UIView.animate(withDuration: 0.5) {
        self.slider.value = round(sender.value)
        self.slider.setValue(round(sender.value), animated: true)
    }
}

我也试过添加 panGesture（没用）：

panGesture = UIPanGestureRecognizer(target: self, action: #selector(panGestureHandler(_:)))
slider.addGestureRecognizer(panGesture)

@objc func panGestureHandler(_ recognizer: UIPanGestureRecognizer){

    let currentPoint = recognizer.location(in: slider)
    let percentage = currentPoint.x/slider.bounds.size.width

    let delta = Float(percentage) * (slider.maximumValue - slider.minimumValue)
    let value = slider.minimumValue + delta
    slider.setValue(round(value), animated: true)
}

如何实现滑块平滑滚动但仍卡入到位？

这是没有进行上述尝试的原始代码：

let slider: UISlider = {
    let slider = UISlider()
    slider.translatesAutoresizingMaskIntoConstraints = false
    slider.minimumValue = 1
    slider.maximumValue = 5
    slider.value = 3
    slider.isContinuous = true
    slider.addTarget(self, action: #selector(onSliderValChanged(_:)), for: .valueChanged)
    return slider
}()

@objc func onSliderValChanged(_ sender: UISlider) {

    slider.value = round(sender.value)
}

func setAnchors() {
    slider.centerYAnchor.constraint(equalTo: view.centerYAnchor, constant: 0).isActive = true
    slider.leftAnchor.constraint(equalTo: view.leftAnchor, constant: 10).isActive = true
    slider.rightAnchor.constraint(equalTo: view.rightAnchor, constant: -10).isActive = true
}

Answer 1

A UISlider 使用几个 UIImageView 子视图绘制自己。当您更改滑块的 value 时，滑块会发送自身 setNeedsLayout，但它实际上不会更改其子视图的框架，直到它在 [=20] 的布局阶段接收到 layoutSubviews =]循环。

要为值的变化设置动画，您需要使滑块在动画块内布置其子视图。因此：

@IBAction func sliderValueChanged(_ slider: UISlider) {
    slider.value = round(slider.value)
    UIView.animate(withDuration: 0.2, animations: {
        slider.layoutIfNeeded()
    })
}

snapping/stepping 如何防止 UISlider 跳到位

How to prevent UISlider from jumping into place while snapping/stepping

ios

swift

scroll

uislider