fix IGListAdapterUpdaterDelegate

Summary: Issue: There's a couple of situations where `IGListAdapterUpdater` updates the `collectionView` without notifying the `IGListAdapterUpdater`. * If we call `reloadDataFallback()` because of a missing window, there's no delegate calls. * If we call `reloadDataFallback()` because of too many diff updates, we call `willPerformBatchUpdatesWithCollectionView` but not `didPerformBatchUpdates`. Fix: Lets clean up the delegate calls * If we `[UICollectioView performBatchUpdates:]` lets call `willPerformBatchUpdatesWithCollectionView` & `didPerformBatchUpdates` * If we fallback to `[UICollectionView reloadData]` lets call `willReloadDataWithCollectionView` & `didReloadDataWithCollectionView` * If we fallback to doing nothing, lets call `didFinishWithoutUpdates` Reviewed By: Haud Differential Revision: D22219236 fbshipit-source-id: 1afb4df8dbbaf4725424027bb52c1a5cc5100b30
Instagram · Jun 26, 2020 · 29bf582 · 29bf582
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -16,6 +16,8 @@ The changelog for `IGListKit`. Also see the [releases](https://github.com/instag
 
 - Remove `[collectionView layoutIfNeeded]` before scrolling in `[IGListAdapter scrollToObject...]` to avoid creating off-screen cells. [Maxime Ollivier](https://github.com/maxolls) (tbd)
 
+- Fixed `IGListAdapterUpdaterDelegate` by 1) calling `willReloadDataWithCollectionView` on fallback reloads and 2) making sure `willPerformBatchUpdatesWithCollectionView` is only called when performing a batch update. [Maxime Ollivier](https://github.com/maxolls) (tbd)
+
 4.0.0
 -----
 ### Breaking Changes

diff --git a/Source/IGListKit/IGListAdapterUpdater.m b/Source/IGListKit/IGListAdapterUpdater.m
@@ -64,6 +64,7 @@ - (void)performReloadDataWithCollectionViewBlock:(IGListCollectionViewBlock)coll
     if (collectionView == nil) {
         [self _cleanStateAfterUpdates];
         executeCompletionBlocks(NO);
+        [_delegate listAdapterUpdater:self didFinishWithoutUpdatesWithCollectionView:collectionView];
         return;
     }
 
@@ -89,11 +90,11 @@ - (void)performReloadDataWithCollectionViewBlock:(IGListCollectionViewBlock)coll
 
     [self _cleanStateAfterUpdates];
 
-    [delegate listAdapterUpdater:self willReloadDataWithCollectionView:collectionView];
+    [delegate listAdapterUpdater:self willReloadDataWithCollectionView:collectionView isFallbackReload:NO];
     [collectionView reloadData];
     [collectionView.collectionViewLayout invalidateLayout];
     [collectionView layoutIfNeeded];
-    [delegate listAdapterUpdater:self didReloadDataWithCollectionView:collectionView];
+    [delegate listAdapterUpdater:self didReloadDataWithCollectionView:collectionView isFallbackReload:NO];
 
     executeCompletionBlocks(YES);
 }
@@ -128,6 +129,7 @@ - (void)performBatchUpdatesWithCollectionViewBlock:(IGListCollectionViewBlock)co
     if (collectionView == nil) {
         [self _cleanStateAfterUpdates];
         executeCompletionBlocks(NO);
+        [_delegate listAdapterUpdater:self didFinishWithoutUpdatesWithCollectionView:collectionView];
         return;
     }
 
@@ -169,26 +171,26 @@ - (void)performBatchUpdatesWithCollectionViewBlock:(IGListCollectionViewBlock)co
     };
 
     void (^reloadDataFallback)(void) = ^{
+        [delegate listAdapterUpdater:self willReloadDataWithCollectionView:collectionView isFallbackReload:YES];
         executeUpdateBlocks();
         [self _cleanStateAfterUpdates];
         [self _performBatchUpdatesItemBlockApplied];
         [collectionView reloadData];
         [collectionView layoutIfNeeded];
-
         executeCompletionBlocks(YES);
+        [delegate listAdapterUpdater:self didReloadDataWithCollectionView:collectionView isFallbackReload:YES];
     };
 
+    // disables multiple performBatchUpdates: from happening at the same time
+    [self _beginPerformBatchUpdatesToObjects:toObjects];
+
     // if the collection view isn't in a visible window, skip diffing and batch updating. execute all transition blocks,
     // reload data, execute completion blocks, and get outta here
     if (self.allowsBackgroundReloading && collectionView.window == nil) {
-        [self _beginPerformBatchUpdatesToObjects:toObjects];
         reloadDataFallback();
         return;
     }
 
-    // disables multiple performBatchUpdates: from happening at the same time
-    [self _beginPerformBatchUpdatesToObjects:toObjects];
-
     const IGListExperiment experiments = self.experiments;
 
     IGListIndexSetResult *(^performDiff)(void) = ^{
@@ -228,6 +230,17 @@ - (void)performBatchUpdatesWithCollectionViewBlock:(IGListCollectionViewBlock)co
         [self _performBatchUpdatesItemBlockApplied];
     };
 
+    // block used as the second param of -[UICollectionView performBatchUpdates:completion:]
+    void (^fallbackWithoutUpdates)(void) = ^(void) {
+        executeCompletionBlocks(NO);
+
+        [delegate listAdapterUpdater:self didFinishWithoutUpdatesWithCollectionView:collectionView];
+
+        // queue another update in case something changed during batch updates. this method will bail next runloop if
+        // there are no changes
+        [self _queueUpdateWithCollectionViewBlock:collectionViewBlock];
+    };
+
     // block used as the second param of -[UICollectionView performBatchUpdates:completion:]
     void (^batchUpdatesCompletionBlock)(BOOL) = ^(BOOL finished) {
         IGListBatchUpdateData *oldApplyingUpdateData = self.applyingUpdateData;
@@ -240,31 +253,37 @@ - (void)performBatchUpdatesWithCollectionViewBlock:(IGListCollectionViewBlock)co
         [self _queueUpdateWithCollectionViewBlock:collectionViewBlock];
     };
 
-    // block that executes the batch update and exception handling
     void (^performUpdate)(IGListIndexSetResult *) = ^(IGListIndexSetResult *result){
+        [delegate listAdapterUpdater:self
+willPerformBatchUpdatesWithCollectionView:collectionView
+                         fromObjects:fromObjects
+                           toObjects:toObjects
+                  listIndexSetResult:result];
+        if (animated) {
+            [collectionView performBatchUpdates:^{
+                batchUpdatesBlock(result);
+            } completion:batchUpdatesCompletionBlock];
+        } else {
+            [UIView performWithoutAnimation:^{
+                [collectionView performBatchUpdates:^{
+                    batchUpdatesBlock(result);
+                } completion:batchUpdatesCompletionBlock];
+            }];
+        }
+    };
+
+    // block that executes the batch update and exception handling
+    void (^tryToPerformUpdate)(IGListIndexSetResult *) = ^(IGListIndexSetResult *result){
         [collectionView layoutIfNeeded];
 
         @try {
-            [delegate  listAdapterUpdater:self
-willPerformBatchUpdatesWithCollectionView:collectionView
-                              fromObjects:fromObjects
-                                toObjects:toObjects
-                       listIndexSetResult:result];
             if (collectionView.dataSource == nil) {
                 // If the data source is nil, we should not call any collection view update.
-                batchUpdatesCompletionBlock(NO);
+                fallbackWithoutUpdates();
             } else if (result.changeCount > 100 && IGListExperimentEnabled(experiments, IGListExperimentReloadDataFallback)) {
                 reloadDataFallback();
-            } else if (animated) {
-                [collectionView performBatchUpdates:^{
-                    batchUpdatesBlock(result);
-                } completion:batchUpdatesCompletionBlock];
             } else {
-                [UIView performWithoutAnimation:^{
-                    [collectionView performBatchUpdates:^{
-                        batchUpdatesBlock(result);
-                    } completion:batchUpdatesCompletionBlock];
-                }];
+                performUpdate(result);
             }
         } @catch (NSException *exception) {
             [delegate listAdapterUpdater:self
@@ -282,12 +301,12 @@ - (void)performBatchUpdatesWithCollectionViewBlock:(IGListCollectionViewBlock)co
         dispatch_async(dispatch_get_global_queue(QOS_CLASS_USER_INITIATED, 0), ^{
             IGListIndexSetResult *result = performDiff();
             dispatch_async(dispatch_get_main_queue(), ^{
-                performUpdate(result);
+                tryToPerformUpdate(result);
             });
         });
     } else {
         IGListIndexSetResult *result = performDiff();
-        performUpdate(result);
+        tryToPerformUpdate(result);
     }
 }
 

diff --git a/Source/IGListKit/IGListAdapterUpdaterDelegate.h b/Source/IGListKit/IGListAdapterUpdaterDelegate.h
@@ -121,16 +121,18 @@ willPerformBatchUpdatesWithCollectionView:(UICollectionView *)collectionView
 
  @param listAdapterUpdater The adapter updater owning the transition.
  @param collectionView The collection view that will be reloaded.
+ @param isFallbackReload The reload was a fallback because we could not performBatchUpdate
  */
-- (void)listAdapterUpdater:(IGListAdapterUpdater *)listAdapterUpdater willReloadDataWithCollectionView:(UICollectionView *)collectionView;
+- (void)listAdapterUpdater:(IGListAdapterUpdater *)listAdapterUpdater willReloadDataWithCollectionView:(UICollectionView *)collectionView isFallbackReload:(BOOL)isFallbackReload;
 
 /**
  Notifies the delegate that the updater successfully called `-[UICollectionView reloadData]`.
 
  @param listAdapterUpdater The adapter updater owning the transition.
  @param collectionView The collection view that reloaded.
+ @param isFallbackReload The reload was a fallback because we could not performBatchUpdate
  */
-- (void)listAdapterUpdater:(IGListAdapterUpdater *)listAdapterUpdater didReloadDataWithCollectionView:(UICollectionView *)collectionView;
+- (void)listAdapterUpdater:(IGListAdapterUpdater *)listAdapterUpdater didReloadDataWithCollectionView:(UICollectionView *)collectionView isFallbackReload:(BOOL)isFallbackReload;
 
 /**
  Notifies the delegate that the collection view threw an exception in `-[UICollectionView performBatchUpdates:completion:]`.
@@ -151,6 +153,14 @@ willPerformBatchUpdatesWithCollectionView:(UICollectionView *)collectionView
                 diffResult:(IGListIndexSetResult *)diffResult
                    updates:(IGListBatchUpdateData *)updates;
 
+/**
+Notifies the delegate that the updater finished without performing any batch updates or reloads
+
+@param listAdapterUpdater The adapter updater owning the transition.
+@param collectionView The collection view that reloaded.
+*/
+- (void)listAdapterUpdater:(IGListAdapterUpdater *)listAdapterUpdater didFinishWithoutUpdatesWithCollectionView:(nullable UICollectionView *)collectionView;
+
 @end
 
 NS_ASSUME_NONNULL_END
diff --git a/Tests/IGListAdapterUpdaterTests.m b/Tests/IGListAdapterUpdaterTests.m
@@ -435,22 +435,20 @@ - (void)test_whenReloadingSection_whenSectionRemoved_thatConvertMethodCorrects {
     XCTAssertEqual(inserts.count, 0);
 }
 
-- (void)test_whenReloadingData_withNilCollectionView_thatDelegateEventNotSent {
+- (void)test_whenReloadingData_withNilCollectionView_thatDelegateFinishesWithoutUpdates {
     id mockDelegate = [OCMockObject mockForProtocol:@protocol(IGListAdapterUpdaterDelegate)];
     self.updater.delegate = mockDelegate;
     id compilerFriendlyNil = nil;
-    [[mockDelegate reject] listAdapterUpdater:self.updater willReloadDataWithCollectionView:compilerFriendlyNil];
-    [[mockDelegate reject] listAdapterUpdater:self.updater didReloadDataWithCollectionView:compilerFriendlyNil];
+    [[mockDelegate expect] listAdapterUpdater:self.updater didFinishWithoutUpdatesWithCollectionView:nil];
     [self.updater performReloadDataWithCollectionViewBlock:^UICollectionView *{ return compilerFriendlyNil; }];
     [mockDelegate verify];
 }
 
-- (void)test_whenPerformingUpdates_withNilCollectionView_thatDelegateEventNotSent {
+- (void)test_whenPerformingUpdates_withNilCollectionView_thatDelegateFinishesWithoutUpdates {
     id mockDelegate = [OCMockObject mockForProtocol:@protocol(IGListAdapterUpdaterDelegate)];
     self.updater.delegate = mockDelegate;
     id compilerFriendlyNil = nil;
-    [[mockDelegate reject] listAdapterUpdater:self.updater willPerformBatchUpdatesWithCollectionView:compilerFriendlyNil fromObjects:@[] toObjects:@[] listIndexSetResult:OCMOCK_ANY];
-    [[mockDelegate reject] listAdapterUpdater:self.updater didPerformBatchUpdates:[OCMArg any] collectionView:compilerFriendlyNil];
+    [[mockDelegate expect] listAdapterUpdater:self.updater didFinishWithoutUpdatesWithCollectionView:nil];
     [self.updater performBatchUpdatesWithCollectionViewBlock:^UICollectionView *{ return compilerFriendlyNil; }];
     [mockDelegate verify];
 }
@@ -517,19 +515,15 @@ - (void)test_whenCollectionViewNotInWindow_andBackgroundReloadFlag_isSetNO_diffH
     [mockDelegate verify];
 }
 
-- (void)test_whenCollectionViewNotInWindow_andBackgroundReloadFlag_isDefaultYES_diffDoesNotHappen {
+- (void)test_whenCollectionViewNotInWindow_andBackgroundReloadFlag_isDefaultYES_fallbackToReload {
     [self.collectionView removeFromSuperview];
 
     id mockDelegate = [OCMockObject niceMockForProtocol:@protocol(IGListAdapterUpdaterDelegate)];
     self.updater.delegate = mockDelegate;
 
-    // NOTE: The current behavior in this case is for the adapter updater
-    // simply not to call any delegate methods at all. This may change
-    // in the future, but we configure the mock delegate to allow any call
-    // except the batch updates calls.
-
-    [[mockDelegate reject] listAdapterUpdater:self.updater willPerformBatchUpdatesWithCollectionView:self.collectionView fromObjects:@[] toObjects:@[] listIndexSetResult:OCMOCK_ANY];
-    [[mockDelegate reject] listAdapterUpdater:self.updater didPerformBatchUpdates:OCMOCK_ANY collectionView:self.collectionView];
+    [mockDelegate setExpectationOrderMatters:YES];
+    [[mockDelegate expect] listAdapterUpdater:self.updater willReloadDataWithCollectionView:self.collectionView isFallbackReload:YES];
+    [[mockDelegate expect] listAdapterUpdater:self.updater didReloadDataWithCollectionView:self.collectionView isFallbackReload:YES];
 
     XCTestExpectation *expectation = genExpectation;
     IGListToObjectBlock to = ^NSArray *{
@@ -544,13 +538,15 @@ - (void)test_whenCollectionViewNotInWindow_andBackgroundReloadFlag_isDefaultYES_
     [mockDelegate verify];
 }
 
-- (void)test_whenCollectionViewNotInWindow_andBackgroundReloadFlag_isDefaultYES_andDataSourceWasSetToNilBefore_thatCollectionViewNotCrash {
+- (void)test_whenCollectionViewNotInWindow_andBackgroundReloadFlag_isDefaultYES_andDataSourceWasSetToNilBefore_fallbackToReload {
     [self.collectionView removeFromSuperview];
 
     id mockDelegate = [OCMockObject niceMockForProtocol:@protocol(IGListAdapterUpdaterDelegate)];
     self.updater.delegate = mockDelegate;
-    [[mockDelegate reject] listAdapterUpdater:self.updater willPerformBatchUpdatesWithCollectionView:self.collectionView fromObjects:@[] toObjects:@[] listIndexSetResult:OCMOCK_ANY];
-    [[mockDelegate reject] listAdapterUpdater:self.updater didPerformBatchUpdates:OCMOCK_ANY collectionView:self.collectionView];
+
+    [mockDelegate setExpectationOrderMatters:YES];
+    [[mockDelegate expect] listAdapterUpdater:self.updater willReloadDataWithCollectionView:self.collectionView isFallbackReload:YES];
+    [[mockDelegate expect] listAdapterUpdater:self.updater didReloadDataWithCollectionView:self.collectionView isFallbackReload:YES];
 
     XCTestExpectation *expectation = genExpectation;
     IGListToObjectBlock to = ^NSArray *{
@@ -731,14 +727,7 @@ - (void)test_whenPerformUpdates_dataSourceWasSetToNil_shouldNotCrash {
     id mockDelegate = [OCMockObject niceMockForProtocol:@protocol(IGListAdapterUpdaterDelegate)];
     self.updater.delegate = mockDelegate;
     [mockDelegate setExpectationOrderMatters:YES];
-    [[mockDelegate expect] listAdapterUpdater:self.updater willPerformBatchUpdatesWithCollectionView:self.collectionView fromObjects:from toObjects:to listIndexSetResult:[OCMArg checkWithBlock:^BOOL(IGListIndexSetResult *result) {
-        if (result.deletes.count != 0 || result.moves.count != 0) {
-            return NO;
-        }
-        // Make sure we note that index 1 is updated (id1 from @[@1] -> @[@2]), and "id2" was inserted at index 1
-        return result.updates.firstIndex == 0 && result.inserts.firstIndex == 1;
-    }]];
-    [[mockDelegate expect] listAdapterUpdater:self.updater didPerformBatchUpdates:OCMOCK_ANY collectionView:self.collectionView];
+    [[mockDelegate expect] listAdapterUpdater:self.updater didFinishWithoutUpdatesWithCollectionView:self.collectionView];
 
     XCTestExpectation *expectation = genExpectation;
-Original file line number
+Diff line change
@@ Expand Up @@
     - Remove `[collectionView layoutIfNeeded]` before scrolling in `[IGListAdapter scrollToObject...]` to avoid creating off-screen cells. [Maxime Ollivier](https://github.com/maxolls) (tbd)
+    - Fixed `IGListAdapterUpdaterDelegate` by 1) calling `willReloadDataWithCollectionView` on fallback reloads and 2) making sure `willPerformBatchUpdatesWithCollectionView` is only called when performing a batch update. [Maxime Ollivier](https://github.com/maxolls) (tbd)
 .0.0
     -----
     ### Breaking Changes
@@ Expand Down @@