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Summary:
I use NSCollectionViews in view controllers that go on and off screen. Some of these view controllers tracks events in the system and update their contents accordingly.

I discovered that, when they do so while currently not in a window, calls to -[NSCollectionView reloadData] are ignored, leading to a crash as the respective view controllers come back into view, since the view controller's model is now out of sync with what the collection view assumes about it (in terms of number of items, number of sections, ..)

Steps to Reproduce:
1) Display content with NSCollectionView
2) Move collection view off-window
3) Change model data and call -reloadData on NSCollectionView

Expected Results:
NSCollectionView invalidates its internal state and requests new data from the data source either immediately or when moving back into a window

Actual Results:
NSCollectionView seems to ignore -reloadData, accessing objects at index paths that are no longer valid, leading to a crash.

Version:
10.13 beta 6 (17A344b)

Notes: