带渐变层的iOS UISLider

Question

我正在构建一个iOS应用程序，其中必须实现自定义UISlider。 问题是内置的UISlider不支持渐变跟踪。 另一个问题是我的UI样式指南显示，当前跟踪值矩形应为两种颜色的渐变，如图中所示

如何构建UISlider的自定义版本？ 我想过要么将现有的子类作为子类，要么通过构建UIControl子类。

我正在使用xcode 9.4和swift 4.2

提前致谢！

Answer 1

我最终通过将渐变层设置为滑块最小轨迹图像的图像来解决了这个问题，如下所示：

@IBDesignable
class GradientSlider: UISlider {

    @IBInspectable var thickness: CGFloat = 20 {
        didSet {
            setup()
        }
    }

    @IBInspectable var sliderThumbImage: UIImage? {
        didSet {
            setup()
        }
    }

    func setup() {
        let minTrackStartColor = Palette.SelectiveYellow
        let minTrackEndColor = Palette.BitterLemon
        let maxTrackColor = Palette.Firefly
        do {
            self.setMinimumTrackImage(try self.gradientImage(
            size: self.trackRect(forBounds: self.bounds).size,
            colorSet: [minTrackStartColor.cgColor, minTrackEndColor.cgColor]),
                                  for: .normal)
            self.setMaximumTrackImage(try self.gradientImage(
            size: self.trackRect(forBounds: self.bounds).size,
            colorSet: [maxTrackColor.cgColor, maxTrackColor.cgColor]),
                                  for: .normal)
            self.setThumbImage(sliderThumbImage, for: .normal)
        } catch {
            self.minimumTrackTintColor = minTrackStartColor
            self.maximumTrackTintColor = maxTrackColor
        }
    }

    func gradientImage(size: CGSize, colorSet: [CGColor]) throws -> UIImage? {
        let tgl = CAGradientLayer()
        tgl.frame = CGRect.init(x:0, y:0, width:size.width, height: size.height)
        tgl.cornerRadius = tgl.frame.height / 2
        tgl.masksToBounds = false
        tgl.colors = colorSet
        tgl.startPoint = CGPoint.init(x:0.0, y:0.5)
        tgl.endPoint = CGPoint.init(x:1.0, y:0.5)

        UIGraphicsBeginImageContextWithOptions(size, tgl.isOpaque, 0.0);
        guard let context = UIGraphicsGetCurrentContext() else { return nil }
        tgl.render(in: context)
        let image = 

    UIGraphicsGetImageFromCurrentImageContext()?.resizableImage(withCapInsets: 
        UIEdgeInsets.init(top: 0, left: size.height, bottom: 0, right: size.height))
        UIGraphicsEndImageContext()
        return image!
    }

    override func trackRect(forBounds bounds: CGRect) -> CGRect {
        return CGRect(
            x: bounds.origin.x,
            y: bounds.origin.y,
            width: bounds.width,
            height: thickness
        )
    }

    override init(frame: CGRect) {
        super.init(frame: frame)
        setup()
    }

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        setup()
    }


}