给带有圆角和方向向下三角形的 Label 设置阴影

概述

如题，实现上述需求

image.png

思路

1. 添加 contentView，contentView 首先添加一个 shapeLayer
2. 继续向 contentView 添加一个 Label，Label.backgroundColor = .clear
3. 在 contentView layoutSubviews() 中配置 shapeLayer，并且 shapeLayer 传入的是 Label.bounds

override func layoutSubviews() {
        super.layoutSubviews()
        configShadowLayer()
}

其中， configShadowLayer() 主要是通过 UIBezierPath 绘制 Label 的形状，并添加阴影

struct CornerRadii {
    let topLeft: CGFloat
    let topRight: CGFloat
    let bottomLeft: CGFloat
    let bottomRight: CGFloat

    init(topLeft: CGFloat, topRight: CGFloat, bottomLeft: CGFloat, bottomRight: CGFloat) {
        self.topLeft = topLeft
        self.topRight = topRight
        self.bottomLeft = bottomLeft
        self.bottomRight = bottomRight
    }
}
    private func CYPathCreateWIthRoundedRect(bounds: CGRect, cornerRadii: CornerRadii) -> UIBezierPath {
        let minX = bounds.minX
        let minY = bounds.minY
        let maxX = bounds.maxX
        let maxY = bounds.maxY

        let topLeftCenterX = minX + cornerRadii.topLeft
        let topLeftCenterY = minY + cornerRadii.topLeft

        let topRightCenterX = maxX - cornerRadii.topRight
        let topRightCenterY = minY + cornerRadii.topRight

        let bottomLeftCenterX = minX + cornerRadii.bottomLeft
        let bottomLeftCenterY = maxY - cornerRadii.bottomLeft

        let bottomRightCenterX = maxX - cornerRadii.bottomRight
        let bottomRightCenterY = maxY - cornerRadii.bottomRight

        let path = UIBezierPath.init()
        path.move(to: CGPoint(x: topLeftCenterX, y: minY))
        // 顶左
        path.addArc(withCenter: CGPoint(x: topLeftCenterX, y: topLeftCenterY), radius: cornerRadii.topLeft, startAngle: CGFloat.pi / 2 * 3, endAngle: CGFloat.pi, clockwise: false)
        path.addLine(to: CGPoint(x: minX, y: bottomLeftCenterY))
        // 底左
        path.addArc(withCenter: CGPoint(x: bottomLeftCenterX, y: bottomLeftCenterY), radius: cornerRadii.bottomLeft, startAngle: CGFloat.pi, endAngle: CGFloat.pi / 2, clockwise: false)
        // 画三角形
        path.addLine(to: CGPoint(x: bottomLeftCenterX + 21, y: maxY))
        path.addLine(to: CGPoint(x: bottomLeftCenterX + 21 + 7, y: maxY + 6.2))
        path.addLine(to: CGPoint(x: bottomLeftCenterX + 21 + 14, y: maxY))

        path.addLine(to: CGPoint(x: bottomRightCenterX, y: maxY))
        // 底右
        path.addArc(withCenter: CGPoint(x: bottomRightCenterX, y: bottomRightCenterY), radius: cornerRadii.bottomRight, startAngle: CGFloat.pi / 2, endAngle: 0, clockwise: false)
        path.addLine(to: CGPoint(x: maxX, y: topRightCenterY))
        // 顶右
        path.addArc(withCenter: CGPoint(x: topRightCenterX, y: topRightCenterY), radius: cornerRadii.topRight, startAngle: 0, endAngle: CGFloat.pi / 2 * 3, clockwise: false)
        path.close()
        return path
    }

    func configShadowLayer() {
        let cornerRadii = CornerRadii(topLeft: 20, topRight: 20, bottomLeft: 20, bottomRight: 20)
        let path = CYPathCreateWIthRoundedRect(bounds: tipsLabel.bounds, cornerRadii: cornerRadii)
        shadowLayer.fillColor = UIColor.white.cgColor
        shadowLayer.path = path.cgPath
        shadowLayer.shadowPath = path.cgPath
        shadowLayer.shadowOpacity = 1
        shadowLayer.shadowColor = UIColor.gray.cgColor
        shadowLayer.shadowRadius =  6
        shadowLayer.shadowOffset = CGSize(width: 0, height: 2)
    }

注意：path.addArc(withCenter: CGPoint(x: topLeftCenterX, y: topLeftCenterY), radius: cornerRadii.topLeft, startAngle: CGFloat.pi / 2 * 3, endAngle: CGFloat.pi, clockwise: false) 中 圆角的startAngle 与 endAngle 均为顺时针角度，具体如图

图一

拓展

1. 有圆角的UIView 添加阴影

思路：

1. view.backgroundColor = .clear
2. 按照上文思路，设置 CAShapeLayer，作为 shadowLayer，然后layer.addSublayer(shadowLayer)，如果所有的圆角半径都一样的话，可以使用如下方法更简单一些

   let berPath = UIBezierPath(roundedRect: bounds, byRoundingCorners: [.topRight , .topLeft, .bottomLeft, .bottomRight], cornerRadii: CGSize(width: 8, height: 8))
   

3. 添加一个 containerView, 其它所有的控件添加到这个 containerView 上，同时设置 containerView.layer.maskToBounds = true， 以及 borderColor、borderWidth 等
4. 如果使用 SnapKit, 需要override func layoutSubviews()，在 layoutSubviews() 方法中调用 生成 shadowLayer 的方法，或者在确定当前 view 尺寸以后再调用也可以。

2. 绘制分别有不同的圆角的 UIView

也可以通过上述方法绘制 UIView 四个角分别有不同的圆角，原理与设置圆角的几种方式类似