---
title: "prepareForTransition(from:)"
framework: uikit
role: symbol
role_heading: Instance Method
path: "uikit/uicollectionviewlayout/preparefortransition(from:)"
---

# prepareForTransition(from:)

Tells the layout object to prepare to be installed as the layout for the collection view.

## Declaration

```swift
func prepareForTransition(from oldLayout: UICollectionViewLayout)
```

## Parameters

- `oldLayout`: The layout object installed in the collection view at the beginning of the transition. You might use this object to provide different ending attributes based on the starting layout object.

## Discussion

Discussion Prior to performing a layout transition, the collection view calls this method so that your layout object can perform any initial calculations needed to generate layout attributes.

## See Also

### Transitioning between layouts

- [prepareForTransition(to:)](uikit/uicollectionviewlayout/preparefortransition(to:).md)
- [finalizeLayoutTransition()](uikit/uicollectionviewlayout/finalizelayouttransition().md)