ARAnnotatedSliderView.m

- (void)show:(BOOL)animated {
	self.alpha = 0.0f;
	self.hidden = NO;
	
	if (animated) {
		[UIView beginAnimations:nil context:nil];
	}
	
	self.alpha = 1.0f;
	
	if (animated) {
		[UIView commitAnimations];
	}
	
	if ([_slider.subviews count] < 3) {
		return;
	}
	
	UIImageView *thumbImageView = (UIImageView *)[_slider.subviews objectAtIndex:2];
	if (![thumbImageView isKindOfClass:[UIImageView class]]) {
		return;
	}
	
	[thumbImageView addObserver:self forKeyPath:kARPageScrubberViewKeypathFrame options:NSKeyValueChangeReplacement context:(void *)thumbImageView];
	[_slider addObserver:self forKeyPath:kARPageScrubberViewKeypathTracking options:NSKeyValueChangeReplacement context:(void *)thumbImageView];
}