ViewController Transition in swift

VCTransition.swift

func transitionToChildViewController(toViewController:UIViewController){
        
        var fromViewController:UIViewController?
        if(self.childViewControllers.count > 0){
            fromViewController = self.childViewControllers[0]
        } else {
            fromViewController = nil;
        }
        
        if(toViewController ==  fromViewController || !self.isViewLoaded()){
            return
        }
        
        let toView:UIView = toViewController.view;
        toView.translatesAutoresizingMaskIntoConstraints = true;
        toView.autoresizingMask = [UIViewAutoresizing.FlexibleWidth,UIViewAutoresizing.FlexibleHeight]
        toView.frame = self.view.bounds
        
        fromViewController?.willMoveToParentViewController(nil);
        self.addChildViewController(toViewController);
        
        // If this is the initial presentation, add the new child with no animation.
        if(fromViewController == nil){
            self.view.addSubview(toViewController.view)
            toViewController.didMoveToParentViewController(self)
            return;
        }
        
        // default animation
        //        self.transitionFromViewController(fromViewController!, toViewController: toViewController, duration: 1.0, options: UIViewAnimationOptions.TransitionFlipFromBottom,animations: nil) { (finished:Bool) -> Void in
        //            //
        //            fromViewController!.removeFromParentViewController()
        //            toViewController.didMoveToParentViewController(self)
        //
        //        }
        
        let width:CGFloat! = self.view.frame.width
        let height:CGFloat! = fromViewController?.view.frame.height
        toViewController.view.frame = CGRectMake(width, 0, width, height)
        self.transitionFromViewController(fromViewController!, toViewController: toViewController, duration: 0.5, options: UIViewAnimationOptions.TransitionNone, animations: { () -> Void in
            //animation
            fromViewController!.view.frame = CGRectMake(0-width, 0, width, height)
            toViewController.view.frame = CGRectMake(0,0,width,height)
            
            }) { (finished:Bool) -> Void in
                //completion
                fromViewController?.removeFromParentViewController()
                toViewController.didMoveToParentViewController(self)
        }
        
    }