self.layer = [CAShapeLayer layer];    self.layer.frame = CGRectMake(0, 0, 100, 100);    self.layer.position = self.view.center;    self.layer.lineWidth = 10.0;    self.layer.fillColor = [UIColor clearColor].CGColor;    self.layer.strokeColor = [UIColor lightGrayColor].CGColor;    self.layer.lineCap = kCALineCapSquare;    /*     CA_EXTERN NSString *const kCALineCapButt     __OSX_AVAILABLE_STARTING (__MAC_10_6, __IPHONE_3_0);     CA_EXTERN NSString *const kCALineCapRound     __OSX_AVAILABLE_STARTING (__MAC_10_6, __IPHONE_3_0);     CA_EXTERN NSString *const kCALineCapSquare     */    UIBezierPath *path = [UIBezierPath bezierPathWithOvalInRect:CGRectMake(0, 0, 100, 100)];    self.layer.path = path.CGPath;    [self.view.layer addSublayer:self.layer];    self.layer.strokeEnd = 0.0;    _progress = 0;    self.timer = [NSTimer scheduledTimerWithTimeInterval:0.1 target:self selector:@selector(updateProgress) userInfo:nil repeats:YES];//更新下载进度_progress += 0.01;    if (self.layer.strokeEnd >= 1) {        self.timer.fireDate = [NSDate distantFuture];    }    else    {        self.layer.strokeEnd = _progress;    }