Rotate image inside UIButton

class IndicatorButton: UIButton {
    
    func setExpanded(expanded: Bool) {
        UIView.beginAnimations(nil, context: nil)
        UIView.setAnimationDelegate(self)
        UIView.setAnimationDuration(0.3)
        UIView.setAnimationCurve(UIViewAnimationCurve.EaseIn)
        imageView?.transform = CGAffineTransformMakeRotation(CGFloat(expanded ? -M_PI : 2 * M_PI))
        UIView.commitAnimations()
    }

}