SWIFT中切換UIContainerView內的Controller

如下，一个UIContainerView内切换两个Controller，当点击登录的时候UIContainerView的视图为LoginController，当点击登记的时候UIContainerView中的视图为RegisterController

在主视图内先做两个按钮的事件。这个不用说啦。当触发按钮事件的时候调用以下代码就可以。

var newController = self.storyboard?.instantiateViewControllerWithIdentifier("RegisterController") as! RegisterController
            let oldController = childViewControllers.last as! UIViewController
            
            oldController.willMoveToParentViewController(nil)
            addChildViewController(newController)
            newController.view.frame = oldController.view.frame

            //isAnimating = true
            transitionFromViewController(oldController, toViewController: newController, duration: 0.1, options: UIViewAnimationOptions.TransitionNone, animations: nil, completion: { (finished) -> Void in
                    oldController.removeFromParentViewController()
                    newController.didMoveToParentViewController(self)
                    //self.isAnimating = false
            })