# transition(from:to:options:completionHandler:) Performs a transition between two sibling child view controllers of the view controller. ``` func transition(from fromViewController: NSViewController, to toViewController: NSViewController, options: NSViewController.TransitionOptions = [], completionHandler completion: (@Sendable () -> Void)? = nil) ``` ## Parameters `fromViewController` A child view controller whose view is visible in the view controller’s view hierarchy. > Note: > The view of this view controller must have a superview, or else this method raises an exception. `toViewController` A child view controller whose view is not in the view controller’s view hierarchy. `options` A bitmask of options that specify how you want to perform the transition animation. For the options, see the [`NSViewController.TransitionOptions`](/documentation/AppKit/NSViewController/TransitionOptions) enumeration. `completion` A block called immediately after the transition animation completes. ## Discussion Use this method to transition between sibling child view controllers owned by a parent view controller (which is the receiver of this method). This method adds the view in the `toViewController` view controller to the superview of the view in the `fromViewController` view controller. Likewise, this method removes the `fromViewController` view from the parent view controller’s view hierarchy at the appropriate time. It is important to allow this method to add and remove these views. > Note: > The receiver of this method must be the parent view controller of the `fromViewController` and `toViewController` view controllers, or else this method raises an exception. To create a parent/child relationship between view controllers, use the [`addChild(_:)`](/documentation/AppKit/NSViewController/addChild(_:)) method or the [`insertChild(_:at:)`](/documentation/AppKit/NSViewController/insertChild(_:at:)) method. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)