Fix for #378 - emptyView not updated when items added

Summary:
Modified `IGListAdapter` to update the `hidden` status of the `emptyView` after any item-level changes (`insertInSectionController:atIndexes:` and related methods) based on whether the item count is zero.

Closes #378

- [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)
Closes https://github.com/Instagram/IGListKit/pull/395

Differential Revision: D4400155

Pulled By: jessesquires

fbshipit-source-id: 6c3422297d86947e7e2878ba1b9227ff2a2a18b4

CHANGELOG.md

@@ -2,6 +2,17 @@
 
 The changelog for `IGListKit`. Also see the [releases](https://github.com/instagram/IGListKit/releases) on GitHub.
 
+2.2.0
+-----
+
+This release closes the [2.2.0 milestone](https://github.com/Instagram/IGListKit/milestone/4).
+
+### Enhancements
+
+### Fixes
+
+- Fix bug where emptyView's hidden status is not updated after the number of items is changed with `insertInSectionController:atIndexes:` or related methods. [Peter Edmonston](https://github.com/edmonston) [(#395)](https://github.com/Instagram/IGListKit/pull/395)
+
 2.1.0
 -----
 

Source/IGListAdapter.m

@@ -504,10 +504,13 @@
         itemCount += [sectionController numberOfItems];
     }
 
-    [self updateBackgroundViewWithItemCount:itemCount];
+    [self updateBackgroundViewShouldHide:itemCount > 0];
 }
 
-- (void)updateBackgroundViewWithItemCount:(NSUInteger)itemCount {
+- (void)updateBackgroundViewShouldHide:(BOOL)shouldHide {
+    if (self.isInUpdateBlock) {
+        return; // will be called again when update block completes
+    }
     UIView *backgroundView = [self.dataSource emptyViewForListAdapter:self];
     // don't do anything if the client is using the same view
     if (backgroundView != _collectionView.backgroundView) {
@@ -516,7 +519,18 @@
         [_collectionView.backgroundView removeFromSuperview];
         _collectionView.backgroundView = backgroundView;
     }
-    _collectionView.backgroundView.hidden = itemCount > 0;
+    _collectionView.backgroundView.hidden = shouldHide;
+}
+
+- (BOOL)itemCountIsZero {
+    __block BOOL isZero = YES;
+    [self.sectionMap enumerateUsingBlock:^(id  _Nonnull object, IGListSectionController<IGListSectionType> * _Nonnull sectionController, NSInteger section, BOOL * _Nonnull stop) {
+        if (sectionController.numberOfItems > 0) {
+            isZero = NO;
+            *stop = YES;
+        }
+    }];
+    return isZero;
 }
 
 - (IGListSectionMap *)sectionMapAdjustForUpdateBlock:(BOOL)adjustForUpdateBlock {
@@ -918,6 +932,7 @@
     } else {
         NSArray *indexPaths = [self indexPathsFromSectionController:sectionController indexes:indexes adjustForUpdateBlock:YES];
         [self.updater reloadItemsInCollectionView:collectionView indexPaths:indexPaths];
+        [self updateBackgroundViewShouldHide:![self itemCountIsZero]];
     }
 }
 
@@ -934,6 +949,7 @@
 
     NSArray *indexPaths = [self indexPathsFromSectionController:sectionController indexes:indexes adjustForUpdateBlock:NO];
     [self.updater insertItemsIntoCollectionView:collectionView indexPaths:indexPaths];
+    [self updateBackgroundViewShouldHide:![self itemCountIsZero]];
 }
 
 - (void)deleteInSectionController:(IGListSectionController<IGListSectionType> *)sectionController atIndexes:(NSIndexSet *)indexes {
@@ -949,6 +965,7 @@
 
     NSArray *indexPaths = [self indexPathsFromSectionController:sectionController indexes:indexes adjustForUpdateBlock:YES];
     [self.updater deleteItemsFromCollectionView:collectionView indexPaths:indexPaths];
+    [self updateBackgroundViewShouldHide:![self itemCountIsZero]];
 }
 
 - (void)reloadSectionController:(IGListSectionController <IGListSectionType> *)sectionController {
@@ -965,6 +982,7 @@
 
     NSIndexSet *sections = [NSIndexSet indexSetWithIndex:section];
     [self.updater reloadCollectionView:collectionView sections:sections];
+    [self updateBackgroundViewShouldHide:![self itemCountIsZero]];
 }
 
 - (void)performBatchAnimated:(BOOL)animated updates:(void (^)())updates completion:(void (^)(BOOL))completion {
@@ -978,7 +996,12 @@
         weakSelf.isInUpdateBlock = YES;
         updates();
         weakSelf.isInUpdateBlock = NO;
-    } completion:completion];
+    } completion: ^(BOOL finished) {
+        [weakSelf updateBackgroundViewShouldHide:![weakSelf itemCountIsZero]];
+        if (completion) {
+            completion(finished);
+        }
+    }];
 }
 
 - (void)scrollToSectionController:(IGListSectionController<IGListSectionType> *)sectionController

Tests/IGListAdapterTests.m

@@ -325,6 +325,60 @@ XCTAssertEqual(CGPointEqualToPoint(point, p), YES); \
     XCTAssertTrue(self.collectionView.backgroundView.hidden);
 }
 
+- (void)test_whenInsertingIntoEmptySection_thatEmptyViewBecomesHidden {
+    self.dataSource.objects = @[@0];
+    self.dataSource.backgroundView = [UIView new];
+    [self.adapter reloadDataWithCompletion:nil];
+    XCTAssertFalse(self.collectionView.backgroundView.hidden);
+    IGListTestSection *sectionController = [self.adapter sectionControllerForObject:@(0)];
+    sectionController.items = 1;
+    [self.adapter insertInSectionController:sectionController atIndexes:[NSIndexSet indexSetWithIndex:0]];
+    XCTAssertTrue(self.collectionView.backgroundView.hidden);
+}
+
+- (void)test_whenDeletingAllItemsFromSection_thatEmptyViewBecomesVisible {
+    self.dataSource.objects = @[@1];
+    self.dataSource.backgroundView = [UIView new];
+    [self.adapter reloadDataWithCompletion:nil];
+    XCTAssertTrue(self.collectionView.backgroundView.hidden);
+    IGListTestSection *sectionController = [self.adapter sectionControllerForObject:@(1)];
+    sectionController.items = 0;
+    [self.adapter deleteInSectionController:sectionController atIndexes:[NSIndexSet indexSetWithIndex:0]];
+    XCTAssertFalse(self.collectionView.backgroundView.hidden);
+}
+
+- (void)test_whenEmptySectionAddsItems_thatEmptyViewBecomesHidden {
+    self.dataSource.objects = @[@0];
+    self.dataSource.backgroundView = [UIView new];
+    [self.adapter reloadDataWithCompletion:nil];
+    XCTAssertFalse(self.collectionView.backgroundView.hidden);
+    IGListTestSection *sectionController = [self.adapter sectionControllerForObject:@(0)];
+    sectionController.items = 2;
+    [self.adapter reloadSectionController:sectionController];
+    XCTAssertTrue(self.collectionView.backgroundView.hidden);
+}
+
+- (void)test_whenSectionItemsAreDeletedAsBatch_thatEmptyViewBecomesVisible {
+    self.dataSource.objects = @[@1, @2];
+    self.dataSource.backgroundView = [UIView new];
+    [self.adapter reloadDataWithCompletion:nil];
+    XCTAssertTrue(self.collectionView.backgroundView.hidden);
+    IGListTestSection *firstSectionController = [self.adapter sectionControllerForObject:@(1)];
+    IGListTestSection *secondSectionController = [self.adapter sectionControllerForObject:@(2)];
+    XCTestExpectation *expectation =  [self expectationWithDescription:NSStringFromSelector(_cmd)];
+    [self.adapter performBatchAnimated:YES updates:^{
+        firstSectionController.items = 0;
+        [self.adapter deleteInSectionController:firstSectionController atIndexes:[NSIndexSet indexSetWithIndex:0]];
+        secondSectionController.items = 0;
+        NSIndexSet *indexesToDelete = [NSIndexSet indexSetWithIndexesInRange:NSMakeRange(0, 2)];
+        [self.adapter deleteInSectionController:secondSectionController atIndexes:indexesToDelete];
+    } completion:^(BOOL finished) {
+        XCTAssertFalse(self.collectionView.backgroundView.hidden);
+        [expectation fulfill];
+    }];
+    [self waitForExpectationsWithTimeout:15 handler:nil];
+}
+
 - (void)test_whenScrollViewDelegateSet_thatDelegateReceivesEvents {
     id mockDelegate = [OCMockObject mockForProtocol:@protocol(UIScrollViewDelegate)];