重绘时未清除UIBezierPath

我有自己的习惯 UIView 在其中我画了一个UIBezierPath。此视图用于UITableViewCell。所以当我滚动时,自定义视图的bezier路径会被重新绘制。问题是新路径会覆盖旧的路径图(上下文没有正确清除)。我打电话来 setNeedsDisplay() 在桌子上,我也把 clearsContextBeforeDrawing = true context.clear(rect) 但这一点都不理想,因为我失去了背景(它变成黑色)。

有没有办法解决这个问题?

class CustomView: UIView {

var percentage: CGFloat = 0 {
    didSet {
        setNeedsDisplay()
    }
}

override init(frame: CGRect) {
    super.init(frame: frame)
    clearsContextBeforeDrawing = true
    contentMode = .redraw
    clipsToBounds = false
}

required init?(coder aDecoder: NSCoder) {
    fatalError("init(coder:) has not been implemented")
}

override func draw(_ rect: CGRect) {
    super.draw(rect)

    // NOTE: don't really like doing this
    let context = UIGraphicsGetCurrentContext()!
    context.clear(rect)

    let center = CGPoint(x: self.bounds.size.width/2, y: self.bounds.size.height/2)

    let path = UIBezierPath(arcCenter: center,
                            radius: self.bounds.size.width/2-10,
                            startAngle: 0.5 * .pi,
                            endAngle: (-2.0 * self.percentage + 0.5) * .pi,
                            clockwise: false)

    path.lineWidth = 4
    UIColor.red.setStroke()
    path.stroke()
}
}

这是设置我的单元格和自定义uiview的地方。

override func tableView(_ tableView: UITableView, cellForItemAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withReuseIdentifier: "cell", for: indexPath)
        let num = list[indexPath.item]
        let percentage = CGFloat(num) / 10
        cell.customView.percentage = percentage // Custom view should get redrawn after this call
        return cell
    }