如何在 Swift 4 的 UIView 中创建带圆角的渐变边框

Question

我想在 UIView 中设置从左到右渐变的边框颜色 [Red, Green]。 比如：

我尝试了以下代码：-

class View: UIView {

    override func layoutSubviews() {
        super.layoutSubviews()

        let path = UIBezierPath(roundedRect: self.bounds, byRoundingCorners: [.topLeft, .bottomLeft, .topRight, .bottomRight], cornerRadii: CGSize(width: frame.size.height / 2, height: frame.size.height / 2))

        let gradient = CAGradientLayer()
        gradient.frame =  CGRect(origin: CGPoint.zero, size: frame.size)
        gradient.colors = [UIColor.green.cgColor, UIColor.red.cgColor]

        let shape = CAShapeLayer()
        shape.lineWidth = 10
        shape.path = path.cgPath
        shape.strokeColor = UIColor.black.cgColor
        shape.fillColor = UIColor.clear.cgColor
        gradient.mask = shape

        layer.insertSublayer(gradient, at: 0)
    }
}

我无法解决三个问题：-
1- 我已将 lineWidth 设置为 10，但它在角落处显示宽度 10，而在水平/垂直处仅显示 5。
2- 我想显示渐变从左到右不是从上到下。

我尝试下面的代码设置从左到右的渐变但不起作用：-

//        gradient.frame =  CGRect(origin: CGPoint.zero, size: frame.size)
        gradient.startPoint = CGPoint(x: 0.0, y: 0.5)
        gradient.endPoint = CGPoint(x: 1.0, y: 0.5)

请帮忙。提前致谢。

Answer 1

编辑

我想设置从左到右的边框

你需要改变 gradient.startPoint 和 gradient.endPoint

enum Direction {
    case horizontal
    case vertical
}

class View: UIView {

init(frame: CGRect, cornerRadius: CGFloat, colors: [UIColor], lineWidth: CGFloat = 5, direction: Direction = .horizontal) {
    super.init(frame: frame)

    self.layer.cornerRadius = cornerRadius
    self.layer.masksToBounds = true
    let gradient = CAGradientLayer()
    gradient.frame = CGRect(origin: CGPoint.zero, size: self.frame.size)
    gradient.colors = colors.map({ (color) -> CGColor in
        color.cgColor
    })

    switch direction {
    case .horizontal:
        gradient.startPoint = CGPoint(x: 0, y: 1)
        gradient.endPoint = CGPoint(x: 1, y: 1)
    case .vertical:
        gradient.startPoint = CGPoint(x: 0, y: 0)
        gradient.endPoint = CGPoint(x: 0, y: 1)
    }

    let shape = CAShapeLayer()
    shape.lineWidth = lineWidth
    shape.path = UIBezierPath(roundedRect: self.bounds.insetBy(dx: lineWidth, 
    dy: lineWidth), cornerRadius: cornerRadius).cgPath
    shape.strokeColor = UIColor.black.cgColor
    shape.fillColor = UIColor.clear.cgColor
    gradient.mask = shape

    self.layer.addSublayer(gradient)
}

required init?(coder aDecoder: NSCoder) {
    fatalError("init(coder:) has not been implemented")
}

如您所见，我添加了一些额外的参数。我通过向 roundedRect 添加插图解决了这个问题：

shape.path = UIBezierPath(roundedRect: self.bounds.insetBy(dx: lineWidth, 
dy: lineWidth), cornerRadius: cornerRadius).cgPath

如何使用：

let myView = View(frame: CGRect(x: 0, y: 0, width: 200, height: 50), cornerRadius: 25, colors: [UIColor.red, .orange, .yellow], lineWidth: 2, direction: .horizontal)
    myView.center = view.center
    view.addSubview(myView)

截图：

roundedViewWithGradient

Answer 2

问题在于贝塞尔路径未在其边界内绘制。它是围绕它的边界绘制的。所以一半的笔划宽度在里面，一半在外面。你需要调整边界来处理这个问题。

将传入贝塞尔路径的框架从 self.bounds 更改为 self.bounds.insetBy(dx: 5, dy: 5)，其中 5 是线宽的一半。

还有台词：

gradient.startPoint = CGPoint(x: 0.0, y: 0.5)
gradient.endPoint = CGPoint(x: 1.0, y: 0.5)

确实导致渐变从左到右。

这是您的完整代码：

class View: UIView {
    override func layoutSubviews() {
        super.layoutSubviews()

        let path = UIBezierPath(roundedRect: self.bounds.insetBy(dx: 5, dy: 5), byRoundingCorners: [.topLeft, .bottomLeft, .topRight, .bottomRight], cornerRadii: CGSize(width: frame.size.height / 2, height: frame.size.height / 2))

        let gradient = CAGradientLayer()
        gradient.frame =  CGRect(origin: CGPoint.zero, size: frame.size)
        gradient.startPoint = CGPoint(x: 0.0, y: 0.5)
        gradient.endPoint = CGPoint(x: 1.0, y: 0.5)
        gradient.colors = [UIColor.green.cgColor, UIColor.red.cgColor]

        let shape = CAShapeLayer()
        shape.lineWidth = 10
        shape.path = path.cgPath
        shape.strokeColor = UIColor.black.cgColor
        shape.fillColor = UIColor.clear.cgColor
        gradient.mask = shape

        layer.insertSublayer(gradient, at: 0)
    }
}