Shake Fields

gistfile1.txt

    private func shakeFieldsAsError() {
        errorFeedback()

        [emailTextField, passwordTextField]
            .enumerated()
            .forEach { (index: Int, element: UITextField?) in

                let c = element!.center
                let ti = TimeInterval(index) * 0.05 // every next field is delayed from previous on 0.05 secs
                let dur: Double = 0.25
                let times = 5
                let xOffset: CGFloat = 15

                UIView.animateKeyframes(
                    withDuration: dur / 2 * Double(times),
                    delay: ti,
                    options: [.allowUserInteraction, .calculationModePaced],
                    animations: {
                        for i in 0 ..< times {
                            UIView.addKeyframe(withRelativeStartTime: dur * Double(i), relativeDuration: dur, animations: {
                                if i == times - 1 {
                                    element?.center = c
                                } else {
                                    let direction: CGFloat = i % 2 == 0 ? 1 : -1
                                    element?.center.x = c.x + xOffset * direction
                                }
                            })
                        }
                    },
                    completion: nil)
            }
    }