在UITableViewCell中绘制阴影导致视觉错误

cell.layer.shadowPath = UIBezierPath(rect: cell.bounds).cgPath

let shadowView = UIView(frame: cell.contentView.bounds)
shadowView.backgroundColor = .white
shadowView.layer.shadowColor = UIColor.black.cgColor
shadowView.layer.shadowOpacity = 0.5
shadowView.layer.shadowOffset = CGSize(width: 0, height: 2)
shadowView.layer.shadowRadius = 4
cell.contentView.addSubview(shadowView)
cell.contentView.sendSubviewToBack(shadowView)

class CustomTableViewCell: UITableViewCell {
    override func drawRect(rect: CGRect) {
        super.drawRect(rect)
        
        let context = UIGraphicsGetCurrentContext()
        context?.setShadow(offset: CGSize(width: 0, height: 2), blur: 4, color: UIColor.black.cgColor)
        context?.setFillColor(UIColor.white.cgColor)
        context?.addRect(bounds)
        context?.fillPath()
    }
}