I am trying to animate a UIView on button click. It does appear on first click but only after that.
@IBAction func viewDetails(sender: AnyObject) {
     UIView.animateWithDuration(0.5 as NSTimeInterval, animations: {
                   println(self.viewDetailsView.center.x)
                    println(self.viewDetailsView.hidden)
                    self.viewDetailsView.hidden = false
                    self.viewDetailsView.center = CGPointMake(self.viewDetailsView.center.x - 4000, self.viewDetailsView.center.y)
                    self.view.layoutIfNeeded()
                    }, completion: {
                        finished in
                        self.detailsVisible = true
                }) }