Add missed delegate call #trivial (#1211)

Summary:
Issue fixed: #

- [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.
- [x] I have reviewed the [contributing guide](https://github.com/Instagram/IGListKit/blob/master/.github/CONTRIBUTING.md)
Pull Request resolved: https://github.com/Instagram/IGListKit/pull/1211

Differential Revision: D9003392

Pulled By: rnystrom

fbshipit-source-id: 73ef837300f8fdb6d9a6005e86f8e9e842827979

CHANGELOG.md

@@ -16,11 +16,12 @@ The changelog for `IGListKit`. Also see the [releases](https://github.com/instag
 
 - Experimental fix to get the `UICollectionView` for batch updating immediately before applying the update. [Ryan Nystrom](https://github.com/rnystrom) (tbd)
 
-
 - `[IGListAdapterUpdater performBatchUpdatesWithCollectionViewBlock:]` and `[IGListAdapterUpdater performReloadDataWithCollectionViewBlock:]` clean state and run completion blocks if their `UICollectionView` is nil. [Brandon Darin](https://github.com/jbd1030) (tbd)
 
 - Ensuring view models with duplicate diff identifiers are removed when view models are first requested by `IGListBindingSectionController` [Adam Stern](https://github.com/adamastern) (tbd)
 
+- Fixed `[IGListAdapterUpdater reloadItemInCollectionView:fromIndexPath:toIndexPath:]` does not call delegate when not inside a batch update. [Bofei Zhu] (https://github.com/zhubofei) [(#1211)](https://github.com/Instagram/IGListKit/pull/1211)
+
 - Log instead of assert for duplicate diff identifiers to make code testable. [Adam Stern](https://github.com/adamastern) (tbd)
 
 3.4.0

Source/IGListAdapterUpdater.m

@@ -534,6 +534,7 @@ static NSUInteger IGListIdentifierHash(const void *item, NSUInteger (*size)(cons
         IGListReloadIndexPath *reload = [[IGListReloadIndexPath alloc] initWithFromIndexPath:fromIndexPath toIndexPath:toIndexPath];
         [self.batchUpdates.itemReloads addObject:reload];
     } else {
+        [self.delegate listAdapterUpdater:self willReloadIndexPaths:@[fromIndexPath] collectionView:collectionView];
         [collectionView reloadItemsAtIndexPaths:@[fromIndexPath]];
     }
 }

Tests/IGListAdapterUpdaterTests.m

@@ -602,6 +602,46 @@
     [self waitForExpectationsWithTimeout:30 handler:nil];
 }
 
+- (void)test_whenNotBatchUpdate_thatDelegateEventsSent {
+    IGSectionObject *object = [IGSectionObject sectionWithObjects:@[@0, @1, @2]];
+    self.dataSource.sections = @[object];
+    [self.collectionView reloadData];
+    
+    id mockDelegate = [OCMockObject niceMockForProtocol:@protocol(IGListAdapterUpdaterDelegate)];
+    self.updater.delegate = mockDelegate;
+    [mockDelegate setExpectationOrderMatters:YES];
+    [[mockDelegate expect] listAdapterUpdater:self.updater willDeleteIndexPaths:OCMOCK_ANY collectionView:self.collectionView];
+    [[mockDelegate expect] listAdapterUpdater:self.updater willInsertIndexPaths:OCMOCK_ANY collectionView:self.collectionView];
+    [[mockDelegate expect] listAdapterUpdater:self.updater
+                        willMoveFromIndexPath:OCMOCK_ANY
+                                  toIndexPath:OCMOCK_ANY
+                               collectionView:self.collectionView];
+    [[mockDelegate expect] listAdapterUpdater:self.updater willReloadIndexPaths:OCMOCK_ANY collectionView:self.collectionView];
+    
+    // This code is of no use, but it will let UICollectionView synchronize number of items,
+    // so it will not crash in following updates. https://stackoverflow.com/a/46751421/2977647
+    [self.collectionView numberOfItemsInSection:0];
+    
+    object.objects = @[@1, @2];
+    [self.updater deleteItemsFromCollectionView:self.collectionView indexPaths:@[
+                                                                                 [NSIndexPath indexPathForItem:0 inSection:0],
+                                                                                 ]];
+    object.objects = @[@1, @2, @4, @5];
+    [self.updater insertItemsIntoCollectionView:self.collectionView indexPaths:@[
+                                                                                 [NSIndexPath indexPathForItem:2 inSection:0],
+                                                                                 [NSIndexPath indexPathForItem:3 inSection:0],
+                                                                                 ]];
+    object.objects = @[@2, @1, @4, @5];
+    [self.updater moveItemInCollectionView:self.collectionView
+                             fromIndexPath:[NSIndexPath indexPathForItem:2 inSection:0]
+                               toIndexPath:[NSIndexPath indexPathForItem:0 inSection:0]];
+    
+    [self.updater reloadItemInCollectionView:self.collectionView
+                               fromIndexPath:[NSIndexPath indexPathForItem:0 inSection:0]
+                                 toIndexPath:[NSIndexPath indexPathForItem:0 inSection:0]];
+    [mockDelegate verify];
+}
+
 - (void)test_whenObjectIdentifiersCollide_withDifferentTypes_thatLookupReturnsNil {
     id testObject = [[IGTestObject alloc] initWithKey:@"foo" value:@"bar"];
     id collision = @"foo";