Display a red border around the textfield and shake it to indicate an error to user.

errorHighlight.swift

// Just call this funtion by passing to it the **required** view to which you wish to draw a user's attention.
func shake(viewToShake: UIView){
        

        
        let colorAnimation = CABasicAnimation(keyPath: "borderColor")
        colorAnimation.fromValue = UIColor.red.cgColor
        colorAnimation.toValue = UIColor.lightGray.cgColor
        viewToShake.layer.borderColor = UIColor.lightGray.cgColor
        viewToShake.layer.borderWidth = 1
        viewToShake.layer.cornerRadius = 5
        
        
        let shakeAnimation = CABasicAnimation(keyPath: "position")
        shakeAnimation.duration = 0.07
        shakeAnimation.repeatCount = 4
        shakeAnimation.autoreverses = false
        shakeAnimation.fromValue = NSValue(cgPoint: CGPoint(x: viewToShake.center.x - 10, y: viewToShake.center.y))
        shakeAnimation.toValue = NSValue(cgPoint: CGPoint(x: viewToShake.center.x + 10, y: viewToShake.center.y))
        
        let errorAnimations = CAAnimationGroup()
        errorAnimations.duration = 0.5
        errorAnimations.animations = [colorAnimation,shakeAnimation]
        errorAnimations.timingFunction = CAMediaTimingFunction(name: kCAMediaTimingFunctionEaseInEaseOut)
        
        viewToShake.layer.add(errorAnimations, forKey: "color and shake")
        
        
    }