http://stackoverflow.com/questions/33994520/how-to-pause-and-resume-uiview-animatewithduration

gistfile1.txt

@IBAction func moveBlock(sender: AnyObject) {
		UIView.animateWithDuration(3, animations: { () -> Void in
			self.viewToAnimate.frame = .zero
		}) { (success) -> Void in
		}
	}
	
	@IBAction func stop(sender: AnyObject) {
		if viewToAnimate.layer.speed == 0 {
			resumeLayer(viewToAnimate.layer)
		} else {
			pauseLayer(viewToAnimate.layer)
		}
	}
	
	// http://stackoverflow.com/questions/33994520/how-to-pause-and-resume-uiview-animatewithduration
	func pauseLayer(layer: CALayer) {
		let pausedTime: CFTimeInterval = layer.convertTime(CACurrentMediaTime(), fromLayer: nil)
		layer.speed = 0.0
		layer.timeOffset = pausedTime
	}
	
	func resumeLayer(layer: CALayer) {
		let pausedTime: CFTimeInterval = layer.timeOffset
		layer.speed = 1.0
		layer.timeOffset = 0.0
		layer.beginTime = 0.0
		let timeSincePause: CFTimeInterval = layer.convertTime(CACurrentMediaTime(), fromLayer: nil) - pausedTime
		layer.beginTime = timeSincePause
	}