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# transitionProgress

The completion percentage of the transition.

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

## Discussion

During the transition, you should set the value of this property periodically and call [`invalidateLayout()`](/documentation/UIKit/UICollectionViewLayout/invalidateLayout()) to force the collection view to update item positions. If you are driving the transition with a gesture recognizer, you would likely set this property from the handler method of your gesture recognizer.

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