swift 绘制下载进度

class ProgressView: UIView {
    // MARK:- 定义属性
    var progress : CGFloat = 0 {
        didSet {
            setNeedsdisplay()
        }
    }
    
    // MARK:- 重写drawRect方法
    override func drawRect(rect: CGRect) {
        super.drawRect(rect)
        // 获取参数
        let center = CGPoint(x: rect.width * 0.5,y: rect.height * 0.5)
        let radius = rect.width * 0.5 - 3
        let startAngle = CGFloat(-M_PI_2)
        let endAngle = CGFloat(2 * M_PI) * progress + startAngle
        
        // 创建贝塞尔曲线
        let path = UIBezierPath(arcCenter: center,radius: radius,startAngle: startAngle,endAngle: endAngle,clockwise: true)
        
        // 绘制一条中心点的线
        path.addLinetoPoint(center)
        path.closePath()
        
        // 设置绘制的颜色
        UIColor(white: 1.0,alpha: 0.4).setFill()
        
        // 开始绘制
        path.fill()
    }

}

progressView.bounds = CGRect(x: 0,y: 0,width: 50,height: 50)
        progressView.center = CGPoint(x: UIScreen.mainScreen().bounds.width * 0.5,y: UIScreen.mainScreen().bounds.height * 0.5)
        
        // 3.设置控件的属性
        progressView.hidden = true
        progressView.backgroundColor = UIColor.clearColor()

// 4.设置imagView的图片
        progressView.hidden = false
        imageView.sd_setimageWithURL(getBigURL(picURL),placeholderImage: image,options: [],progress: { (current,total) -> Void in
            self.progressView.progress = CGFloat(current) / CGFloat(total)
            }) { (_,_,_) -> Void in
                self.progressView.hidden = true
        }