iOS 带有渐变层的 UISLider

Question

我正在构建一个 iOS 应用程序，我必须在其中实现自定义 UISlider。问题是内置的 UISlider 不支持渐变轨道。另一个问题是我的 UI 样式指南显示当前跟踪值矩形应该是两种颜色的渐变，如图所示

如何构建自定义版本的 UISlider？我考虑过将现有的子类化或构建一个 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道图像的图像解决了问题，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()
    }


}

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