Summary:
Adding a new layout-invalidation API, telling the layout object to query and rebuild the layout for all items in the section controller. This works with `UICollectionViewFlowLayout` and should work with other custom layouts (including our own).
Issue fixed: #360, #459
- [x] All tests pass. Demo project builds and runs.
- [x] I added tests, an experiment, or detailed why my change isn't tested.
- [x] I added an entry to the `CHANGELOG.md` for any breaking changes, enhancements, or bug fixes.
Closes https://github.com/Instagram/IGListKit/pull/499
Reviewed By: jessesquires
Differential Revision: D4590274
Pulled By: rnystrom
fbshipit-source-id: f87235be4e6c024bf979b831a8938be68895e011
Summary:
I was able to build a unit test that reproduces the issue. We can avoid the crash by simply returning `nil` when accessing a cell while working range events are being vended.
There is definitely something weird going on here though. When debugging `cellForItemAtIndexPath:` I found:
```
(lldb) po indexPath
<NSIndexPath: 0xc000000000000516> {length = 2, path = 5 - 0}
(lldb) po [[self collectionView] numberOfSections]
11
```
So in theory we should be fine, right? But when I continue I get
```
*** Assertion failure in -[UICollectionViewData numberOfItemsBeforeSection:], /BuildRoot/Library/Caches/com.apple.xbs/Sources/UIKit_Sim/UIKit-3600.5.2/UICollectionViewData.m:611
*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'request for number of items before section 5 when there are only 3 sections in the collection view'
```
There _were_ 3 sections in the UICV before the update, but the data source and structure powering
Closes https://github.com/Instagram/IGListKit/pull/216
Differential Revision: D4204625
Pulled By: rnystrom
fbshipit-source-id: 455ed199dfc115077e4294e2843016a50e179015
