* [ASCollectionNode] Add -isProcessingUpdates and -onDidFinishProcessingUpdates: APIs.
Over time, there have actually been a lot of legitimate uses for an API like this.
In fact, I'm not quite sure what has held us back from adding one!
I believe that at least some portion of -wait calls (even if less than 50%) could be
replaced with -onDidFinishProcessingUpdates:, which could potentially improve the
performance of applications using -wait by a significant amount.
Please take a close look at implementation correctness. Although I'm in a bit of a
rush, I'm aiming to make this properly documented and added a basic test -- but it
could certainly use some more detailed testing as a followup.
* [ASCollectionNode] Improvements to the implementation of -isProcessingUpdates and -onDidFinishProcessingUpdates:
* Add lock to ASMainSerialQueue count method.
* [ASTableNode] Implement -isProcessingUpdates and -onDidFinishProcessingUpdates:. Rename -waitUntil to consistent naming.
* Add _ASCollectionReusableView container for ASCollectionNode supplementary nodes with applyLayoutAttributes support
• Adds support for -[ASCellNode applyLayoutAttributes:] to supplementary nodes
* Ensure _ASCollectionReusableView has layoutAttributes if the collection view doesn’t set them
* Use correct layoutAttributes accessor for supplementary elements
* Add unit test to test trait collection changes occur during updates are handles correctly
* Remove handling code in ASDataController:updateWithChangeSet. Previous test should fail
* Correctly handle trait collection changes that occur mid-updates
- Currently, when there is a new trait collection, we correctly propagate it to all visible elements. However, since the propagating block is executed on main thread immediately without waiting for the background editing queue of ASDataController, not all elements are updated.
- Then to fix that, we updated ASDataController to handle these changes inside updateWithChangeSet. This works, but it doesn’t address the underlying issue.
- We now delegate the propagating task to ASDataController which schedule a block to its main serial queue after waiting for its background editing queue.
