Animating only the image in UIBarButtonItem

Question

Ive seen this effect in 2 apps and I REALLY want to find how to do it.

The animation is in a UIBarButtonItem, and is only to the image. The image is a + symbol, and

Answer 1

Recently had to do the same thing in Swift. I created a tutorial that includes starter and final projects, and goes step-by-step with some tips sprinkled in. The code looks like this:

@IBOutlet weak var rightBarButton: UIBarButtonItem! {
    didSet {
        let icon = UIImage(named: "star")
        let iconSize = CGRect(origin: CGPointZero, size: icon!.size)
        let iconButton = UIButton(frame: iconSize)
        iconButton.setBackgroundImage(icon, forState: .Normal)
        rightBarButton.customView = iconButton
        rightBarButton.customView!.transform = CGAffineTransformMakeScale(0, 0)

        UIView.animateWithDuration(1.0,
            delay: 0.5,
            usingSpringWithDamping: 0.5,
            initialSpringVelocity: 10,
            options: .CurveLinear,
            animations: {
                self.rightBarButton.customView!.transform = CGAffineTransformIdentity
            },
            completion: nil
        )    

        iconButton.addTarget(self, action: "tappedRightButton", forControlEvents: .TouchUpInside)        
    }
}

func tappedRightButton(){
    rightBarButton.customView!.transform = CGAffineTransformMakeRotation(CGFloat(M_PI * 6/5))
    UIView.animateWithDuration(1.0) {
        self.rightBarButton.customView!.transform = CGAffineTransformIdentity
    }
}