<!--
{
  "availability" : [
    "macOS: 10.11.0 -"
  ],
  "documentType" : "symbol",
  "framework" : "AppKit",
  "identifier" : "/documentation/AppKit/NSCollectionViewTransitionLayout/transitionProgress",
  "metadataVersion" : "0.1.0",
  "role" : "Instance Property",
  "symbol" : {
    "kind" : "Instance Property",
    "modules" : [
      "AppKit"
    ],
    "preciseIdentifier" : "c:objc(cs)NSCollectionViewTransitionLayout(py)transitionProgress"
  },
  "title" : "transitionProgress"
}
-->

# transitionProgress

The completion percentage of the transition.

```
var transitionProgress: CGFloat { get set }
```

## Discussion

During the transition, set the value of this property periodically and call the [`invalidateLayout()`](/documentation/AppKit/NSCollectionViewLayout/invalidateLayout()) method to force the collection view to update item positions. For example, when driving a transition using a gesture recognizer, you can set this property from the handler method of your gesture recognizer.

---

Copyright &copy; 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)