Semi-transparent overlay for UIButton subclass

A little snippet for subclassed UIButton that adds an UIImageView overlay.
You can then animate the alpha property.

- (void)awakeFromNib
{
 UIImage *img = [self imageForState:UIControlStateSelected];
 overlayImage = [[UIImageView alloc] initWithImage:img];
 overlayImage.alpha = 0.0f;
 [self addSubview:overlayImage];
 // [self addTarget:self action:@selector(buttonClicked:) forControlEvents:UIControlEventTouchDown];
 // you could call custom highlight handler
}

- (void)setHighlightedByAlpha:(BOOL)highlighted
{
 [UIView beginAnimations:nil context:@"hmm"];
 [UIView setAnimationCurve: UIViewAnimationCurveLinear];
 [UIView setAnimationDuration:0.2f];
 overlayImage.alpha = highlighted ? 1.0f : 0.0f;
 [UIView commitAnimations];
}