显示CGRect边框的简单方法？

let borderLayer = CAShapeLayer()
borderLayer.frame = CGRect(x: 0, y: 0, width: 100, height: 100)
view.layer.addSublayer(borderLayer)

let borderPath = UIBezierPath(roundedRect: CGRect(x: 0, y: 0, width: 100, height: 100), cornerRadius: 0)
borderLayer.path = borderPath.cgPath
borderLayer.fillColor = UIColor.clear.cgColor
borderLayer.strokeColor = UIColor.red.cgColor
borderLayer.lineWidth = 1

class CustomView: UIView {

    override func draw(_ rect: CGRect) {
        let borderLayer = CALayer()
        borderLayer.frame = rect
        borderLayer.backgroundColor = UIColor.red.cgColor
        borderLayer.borderColor = UIColor.red.cgColor
        borderLayer.borderWidth = 1
        addSubview(borderLayer)

        let borderPath = UIBezierPath(roundedRect: rect, cornerRadius: 0)
        borderLayer.path = borderPath.cgPath
        borderLayer.fill()
    }
}

let context = CGContext(data: nil, width: 100, height: 100, bitsPerComponent: 8, bytesPerRow: 0, space: CGColorSpaceCreateDeviceGray(), attributes: nil, context: nil)

let rect = CGRect(x: 0, y: 0, width: 100, height: 100)

context.setStrokeColor(UIColor.red.cgColor)
context.setLineWidth(1)
context.move(to: CGPoint(x: 0, y: 0))
context.addLine(to: CGPoint(x: 100, y: 100))
context.strokePath()