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# beginAppearanceTransition(_:animated:)

Tells a child controller its appearance is about to change.

```
func beginAppearanceTransition(_ isAppearing: Bool, animated: Bool)
```

## Parameters

`isAppearing`

<doc://com.apple.documentation/documentation/Swift/true> if the child view controller’s view is about to be added to the view hierarchy, <doc://com.apple.documentation/documentation/Swift/false> if it is being removed.

`animated`

If <doc://com.apple.documentation/documentation/Swift/true>, the transition is being animated.

## Discussion

If you are implementing a custom container controller, use this method to tell the child that its views are about to appear or disappear. Do not invoke [`viewWillAppear(_:)`](/documentation/UIKit/UIViewController/viewWillAppear(_:)), [`viewWillDisappear(_:)`](/documentation/UIKit/UIViewController/viewWillDisappear(_:)), [`viewDidAppear(_:)`](/documentation/UIKit/UIViewController/viewDidAppear(_:)), or [`viewDidDisappear(_:)`](/documentation/UIKit/UIViewController/viewDidDisappear(_:)) directly.

---

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