_demoView = [[UIView alloc] initWithFrame:CGRectMake(100, 100, 100, 100)];

    [self.view addSubview:_demoView];

    CAShapeLayer *shapeLayer = [CAShapeLayer layer];

    shapeLayer.frame = _demoView.bounds;

    UIBezierPath *path = [UIBezierPath bezierPathWithOvalInRect:_demoView.bounds];

    shapeLayer.path = path.CGPath;

//    shapeLayer.strokeEnd = 1.0f;

//    shapeLayer.strokeStart = 0.75f;

    shapeLayer.fillColor = [UIColor clearColor].CGColor;

    shapeLayer.lineWidth = 2.0f;

    shapeLayer.strokeColor = [UIColor redColor].CGColor;

    [_demoView.layer addSublayer:shapeLayer];

    CABasicAnimation *pathAnima = [CABasicAnimation animationWithKeyPath:@"strokeEnd"];

    pathAnima.duration = 3.0f;

    pathAnima.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseOut];

    pathAnima.fromValue = [NSNumber numberWithFloat:0.0f];

    pathAnima.toValue = [NSNumber numberWithFloat:1.0f];

    pathAnima.fillMode = kCAFillModeForwards;

    pathAnima.removedOnCompletion = NO;

    [shapeLayer addAnimation:pathAnima forKey:@"strokeEndAnimation"];