iOS 绘图

自定义 UIView 类，重写 draw() 方法并调用 UIBezierPath 类相关方法
自定义 UIView 类，重写 draw() 方法并调用 UIGraphicsGetCurrentContext 类相关方法
UIBezierPath 类与 CAShaperLayer 类搭配

draw + UIBezierPath

    override func draw(_ rect: CGRect) {
        super.draw(rect)
        
        print("=========== \(#function)")
        
//        //设定颜色，并绘制它们
        UIColor.systemRed.setFill()
        UIColor.systemBlue.setStroke()
        
        //创建一个矩形，它的所有边都内缩5%
        let drawingRect = self.bounds.insetBy(dx: self.bounds.size.width * 0.05, dy: self.bounds.size.height * 0.05)
        
        //确定组成绘画的点 
        let rightMid = CGPoint(x: drawingRect.maxX, y: drawingRect.midY) 
        let leftMid = CGPoint(x: drawingRect.minX, y: drawingRect.midY)

        // 绘制水平线
        let lineBezierPath = UIBezierPath()
        lineBezierPath.move(to: leftMid)
        lineBezierPath.addLine(to: rightMid)
        lineBezierPath.lineWidth = 10
        lineBezierPath.stroke()
    }

draw + UIGraphicsGetCurrentContext (CGContext)

    override func draw(_ rect: CGRect) {
        super.draw(rect)
        
        //获取绘图上下文
        guard let context = UIGraphicsGetCurrentContext() else {
            return
        }
        
        //创建一个矩形，它的所有边都内缩3
        let drawingRect = self.bounds.insetBy(dx: 3, dy: 3)
        
        //创建并设置路径
        let path = CGMutablePath()
        
        //圆弧半径
        let radius = min(drawingRect.width, drawingRect.height)/2
        //圆弧中点
        let center = CGPoint(x:drawingRect.midX, y:drawingRect.midY)
        //绘制圆弧
        path.addArc(center: center, radius: radius, startAngle: 0,
                    endAngle: CGFloat.pi * 1.5, clockwise: false)
        
        //添加路径到图形上下文
        context.addPath(path)
        
        //设置笔触颜色
        context.setStrokeColor(UIColor.orange.cgColor)
        //设置笔触宽度
        context.setLineWidth(6)
        
        //绘制路径
        context.strokePath()
    }

UIBezierPath + CAShaperLayer

    /// 画圆角
    func roundCorners(_ corners: UIRectCorner, radius: CGFloat) {
        let maskPath = UIBezierPath(
            roundedRect: self.bounds,
            byRoundingCorners: corners,
            cornerRadii: CGSize(width: radius, height: radius)
        )

        let shape = CAShapeLayer()
        shape.path = maskPath.cgPath
        layer.mask = shape
    }