[CDS] Fix appearance tracking

[benlodotcom]

Fix #129, indexPath is not a reliable thing to use for disappearance announcements on deletion (either the index would be out of bounds if the last item is deleted or it will point to an invalid item).

Calling - (void)announceWillAppearForItemInCell:(UICollectionViewCell *)cell atIndexPath:(NSIndexPath *)indexPath and - (void)announceDidDisappearForItemInCell:(UICollectionViewCell *)cell atIndexPath:(NSIndexPath *)indexPath guarantees the announcement will be dispatched to the component tree associated to the cell.

It is however non opinionated in the sense that it won't do deduplication of events, or check for imbalanced calls.
For instance while reloading a cell on screen, the collection view first send appearance events for the newly created cell and then send disappearance events for the old cell, this situation should be handled properly in the controller layer. #153 has been opened to track these use cases and provide examples/code to deal with them.

[adamjernst]

Nice. Since we're now not even using the index path parameter from the announce... methods, mind removing it?

[benlodotcom]

Kept it for API symmetry but totally fine removing it.

[adamjernst]

I do like the symmetry but... #yagni

On Apr 28, 2015, at 11:51 AM, Benjamin Loulier notifications@github.com wrote:

Kept it for API symmetry but totally fine removing it.

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