Add allowsBackgroundReloading Flag to ListAdapterUpdater to Give User Control of Behavior

CHANGELOG.md

@@ -19,6 +19,8 @@ This release closes the [2.1.0 milestone](https://github.com/Instagram/IGListKit
 
 - Added CocoaPods subspec for diffing, `IGListKit/Diffing` and an [installation guide](https://instagram.github.io/IGListKit/installation.html). [Sherlouk](https://github.com/Sherlouk) [(#368)](https://github.com/Instagram/IGListKit/pull/368)
 
+- Added `allowsBackgroundReloading` flag (default `YES`) to `IGListAdapterUpdater` so users can configure this behavior as needed. [Adlai-Holler](https://github.com/Adlai-Holler) [(#375)](https://github.com/Instagram/IGListKit/pull/375)
+
 ### Fixes
 
 - Avoid `UICollectionView` crashes when queueing a reload and insert/delete on the same item as well as reloading an item in a section that is animating. [Ryan Nystrom](https://github.com/rnystrom) [(#325)](https://github.com/Instagram/IGListKit/pull/325)

Source/IGListAdapterUpdater.h

@@ -37,6 +37,17 @@ IGLK_SUBCLASSING_RESTRICTED
  */
 @property (nonatomic, assign) BOOL movesAsDeletesInserts;
 
+/**
+ A flag indicating whether this updater should skip diffing and simply call
+ `reloadData` for updates when the collection view is not in a window. The default value is `YES`.
+
+ @note This will result in better performance, but will not generate the same delegate
+ callbacks. If using a custom layout, it will not receive `prepareForCollectionViewUpdates:`.
+
+ @warning On iOS < 8.3, this behavior is unsupported and will always be treated as `NO`.
+ */
+@property (nonatomic, assign) BOOL allowsBackgroundReloading;
+
 /**
  A bitmask of experiments to conduct on the updater.
  */

Source/IGListAdapterUpdater.m

@@ -16,9 +16,7 @@
 
 #import "UICollectionView+IGListBatchUpdateData.h"
 
-@implementation IGListAdapterUpdater {
- BOOL _canBackgroundReload;
-}
+@implementation IGListAdapterUpdater
 
 - (instancetype)init {
  IGAssertMainThread();
@@ -36,7 +34,7 @@ - (instancetype)init {
  _insertIndexPaths = [[NSMutableSet alloc] init];
  _reloadIndexPaths = [[NSMutableSet alloc] init];
 
- _canBackgroundReload = [[[UIDevice currentDevice] systemVersion] compare:@"8.3" options:NSNumericSearch] != NSOrderedAscending;
+ _allowsBackgroundReloading = YES;
  }
  return self;
 }
@@ -155,7 +153,8 @@ - (void)performBatchUpdatesWithCollectionView:(UICollectionView *)collectionView
 
  // 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 (_canBackgroundReload && collectionView.window == nil) {
+ const BOOL iOS83OrLater = (NSFoundationVersionNumber >= NSFoundationVersionNumber_iOS_8_3);
+ if (iOS83OrLater && self.allowsBackgroundReloading && collectionView.window == nil) {
  [self beginPerformBatchUpdatestoObjects:toObjects];
  executeUpdateBlocks();
  [self cleanupUpdateBlockState];

Tests/IGListAdapterUpdaterTests.m

@@ -459,4 +459,50 @@ - (void)test_whenCallingReloadData_withUICollectionViewFlowLayout_withEstimatedS
  XCTAssertEqual([collectionView numberOfItemsInSection:1], 4);
 }
 
+- (void)test_whenCollectionViewNotInWindow_andBackgroundReloadFlag_isSetNO_diffHappens {
+ self.updater.allowsBackgroundReloading = NO;
+ [self.collectionView removeFromSuperview];
+
+ id mockDelegate = [OCMockObject niceMockForProtocol:@protocol(IGListAdapterUpdaterDelegate)];
+ self.updater.delegate = mockDelegate;
+ [mockDelegate setExpectationOrderMatters:YES];
+ [[mockDelegate expect] listAdapterUpdater:self.updater willPerformBatchUpdatesWithCollectionView:self.collectionView];
+ [[mockDelegate expect] listAdapterUpdater:self.updater didPerformBatchUpdates:OCMOCK_ANY withCollectionView:self.collectionView];
+
+ XCTestExpectation *expectation = genExpectation;
+ NSArray *to = @[
+ [IGSectionObject sectionWithObjects:@[]]
+ ];
+ [self.updater performUpdateWithCollectionView:self.collectionView fromObjects:self.dataSource.sections toObjects:to animated:NO objectTransitionBlock:self.updateBlock completion:^(BOOL finished) {
+ [expectation fulfill];
+ }];
+ waitExpectation;
+ [mockDelegate verify];
+}
+
+- (void)test_whenCollectionViewNotInWindow_andBackgroundReloadFlag_isDefaultYES_diffDoesNotHappen {
+ [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];
+ [[mockDelegate reject] listAdapterUpdater:self.updater didPerformBatchUpdates:OCMOCK_ANY withCollectionView:self.collectionView];
+
+ XCTestExpectation *expectation = genExpectation;
+ NSArray *to = @[
+ [IGSectionObject sectionWithObjects:@[]]
+ ];
+ [self.updater performUpdateWithCollectionView:self.collectionView fromObjects:self.dataSource.sections toObjects:to animated:NO objectTransitionBlock:self.updateBlock completion:^(BOOL finished) {
+ [expectation fulfill];
+ }];
+ waitExpectation;
+ [mockDelegate verify];
+}
+
 @end