ios - 透明的 UIButton 标题

Question

如何从按钮背景中减去标题文本的形状？

我创建了一个自定义的 UIButton 类。目前添加边框和文本颜色的代码看起来很简单

layer.borderWidth = 2.0
layer.borderColor = buttonColor.CGColor
layer.cornerRadius = (CGFloat(bounds.height) + paddingVertical * 2.0) / 2.0
setTitleColor(buttonColor, forState: UIControlState.Normal)

关于如何从背景中减去按钮标题形状的任何建议。我需要将所有这些渲染为图像还是有更好的选择？

Answer 1

swift 4 的扩展

extension UIButton{
func clearColorForTitle() {

    let buttonSize = bounds.size

    if let font = titleLabel?.font{
        let attribs = [NSAttributedStringKey.font: font]

        if let textSize = titleLabel?.text?.size(withAttributes: attribs){
            UIGraphicsBeginImageContextWithOptions(buttonSize, false, UIScreen.main.scale)

            if let ctx = UIGraphicsGetCurrentContext(){
                ctx.setFillColor(UIColor.white.cgColor)

                let center = CGPoint(x: buttonSize.width / 2 - textSize.width / 2, y: buttonSize.height / 2 - textSize.height / 2)
                let path = UIBezierPath(rect: CGRect(x: 0, y: 0, width: buttonSize.width, height: buttonSize.height))
                ctx.addPath(path.cgPath)
                ctx.fillPath()
                ctx.setBlendMode(.destinationOut)

                titleLabel?.text?.draw(at: center, withAttributes: [NSAttributedStringKey.font: font])

                if let viewImage = UIGraphicsGetImageFromCurrentImageContext(){
                    UIGraphicsEndImageContext()

                    let maskLayer = CALayer()
                    maskLayer.contents = ((viewImage.cgImage) as AnyObject)
                    maskLayer.frame = bounds

                    layer.mask = maskLayer
                }
            }
        }
    }
}

用法:

button.clearColorForTitle()