iOS空心圆下载进度指示器控件

self.layer = [CAShapeLayer layer];

    self.layer.frame = CGRectMake(, , , );

    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(, , , )];

    self.layer.path = path.CGPath;

    [self.view.layer addSublayer:self.layer];

    self.layer.strokeEnd = 0.0;

    _progress = ;

    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 >= ) {

        self.timer.fireDate = [NSDate distantFuture];

    }

    else

    {

        self.layer.strokeEnd = _progress;

    }