Swift 4 Xcode 9 UISlider 3 颜色从一开始就可见

Question

如何在 swift 4 Xcode 9 中制作黄色、绿色、红色 3 种颜色的滑块？它们应该按这个顺序排列，如果您启动应用程序，您会看到它是一个 3 色滑块。没有 tintcolored 滑块在拇指所在位置后会改变颜色。即使没有与之交互，它也应该是三色的。滑块拇指应在滑块颜色之后改变颜色。

Answer 1

我使用 CAGradientLayer 来设计滑块的最大和最小轨道图像，并为滑块拇指图像设计一个矩形。随意根据您的需要定制它

 func setSlider(slider:UISlider) {
    let tgl = CAGradientLayer()
    let frame = CGRect(x: 0.0, y: 0.0, width: slider.bounds.width, height: 20.0 )
    tgl.frame = frame

    tgl.colors = [UIColor.red.cgColor, UIColor.yellow.cgColor, UIColor.green.cgColor]

    tgl.borderWidth = 1.0
    tgl.borderColor = UIColor.gray.cgColor
    tgl.cornerRadius = 5.0

    tgl.endPoint = CGPoint(x: 1.0, y:  1.0)
    tgl.startPoint = CGPoint(x: 0.0, y:  1.0)

    UIGraphicsBeginImageContextWithOptions(tgl.frame.size, false, 0.0)
    tgl.render(in: UIGraphicsGetCurrentContext()!)
    let backgroundImage = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()

    slider.setMaximumTrackImage(backgroundImage?.resizableImage(withCapInsets:.zero),  for: .normal)
    slider.setMinimumTrackImage(backgroundImage?.resizableImage(withCapInsets:.zero),  for: .normal)

    let layerFrame = CGRect(x: 0, y: 0, width: 10.0, height: 30.0)

    let shapeLayer = CAShapeLayer()
    shapeLayer.path = CGPath(rect: layerFrame, transform: nil)
    shapeLayer.fillColor = UIColor.black.cgColor

    let thumb = CALayer.init()
    thumb.frame = layerFrame
    thumb.addSublayer(shapeLayer)

    UIGraphicsBeginImageContextWithOptions(thumb.frame.size, false, 0.0)

    thumb.render(in: UIGraphicsGetCurrentContext()!)
    let thumbImage = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()

    slider.setThumbImage(thumbImage, for: .normal)
    slider.setThumbImage(thumbImage, for: .highlighted)
}