Open Radar

 
Summary:
When collection view is updating data, -[UICollectionViewLayout prepareForCollectionViewUpdates:] should be called before prepareLayout and layoutAttributesForElementsInRect: method

Steps to Reproduce:
1. Subclass UICollectionViewLayout that is calculate the element layout attributes lazily.
2. Implement the update layout and data methods.
3. Manipulate the UICollectionView items.


Expected Results:
Method called on the subclass should be prepareForCollectionViewUpdates: -> prepareLayout -> layoutAttributesForElementsInRect:

Actual Results:
Method called on the subclass is prepareLayout -> layoutAttributesForElementsInRect: -> prepareForCollectionViewUpdates


Regression:
Describe circumstances where the problem occurs or does not occur, such as software versions and/or hardware configurations.

Notes:
I think prepareForCollectionViewUpdates: method is the best method for manipulate the layout attributes data when the collection view's items is updated. It let developer to implement the updating layout attributes for the updated data before the layout is asked for the newly showed attributes.