Fix inconsistent state caused in UICollectionViewLayout+InteractiveRe…

…ordering. (Instagram#1289)

Summary:
Issue fixed: Instagram#1288

- [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: Instagram#1289

Reviewed By: timonus

Differential Revision: D13590406

Pulled By: rnystrom

fbshipit-source-id: 0814b0c2383a185da747176bad57dfb15c7e883f

CHANGELOG.md

@@ -29,6 +29,8 @@ The changelog for `IGListKit`. Also see the [releases](https://github.com/instag
 
 - Fixed binding section controllers failing to update their cells when the section controller's section changes. [Chrisna Aing](https://github.com/ccrazy88) [(#1144)](https://github.com/Instagram/IGListKit/pull/1144)
 
+- Fixed a bug caused when applying interactive reordering on a single section item while dragging it through the last spot of the collection view and back to some (non-last) target position. [Ofir Gluzman](https://github.com/ofirgluzman) [#1289](https://github.com/Instagram/IGListKit/pull/1289)
+
 3.2.0
 -----
 

Source/Internal/UICollectionViewLayout+InteractiveReordering.m

@@ -95,6 +95,8 @@ - (nullable NSIndexPath *)updatedTargetForInteractivelyMovingItem:(NSIndexPath *
     IGListSectionController *sourceSectionController = [adapter sectionControllerForSection:sourceSectionIndex];
     IGListSectionController *destinationSectionController = [adapter sectionControllerForSection:destinationSectionIndex];
 
+    adapter.isLastInteractiveMoveToLastSectionIndex = NO;
+
     // this is a reordering of sections themselves
     if ([sourceSectionController numberOfItems] == 1
         && [destinationSectionController numberOfItems] == 1) {

Tests/IGListAdapterTests.m

@@ -1727,4 +1727,34 @@ - (void)test_whenItemsAreInteractivelyReorderedAcrossSections_thatIndexesRevertT
     XCTAssertEqual(section1Objects[2], section1.sectionObject.objects[2]);
 }
 
+- (void)test_whenSingleItemInSectionIsInteractivelyReorderedThorughLastSpot_indexesUpdateCorrectly {
+    IGListTestAdapterReorderingDataSource *dataSource = [IGListTestAdapterReorderingDataSource new];
+    dataSource.objects = @[@0, @1, @2];
+    self.adapter.dataSource = dataSource;
+    self.adapter.moveDelegate = dataSource;
+
+    IGTestReorderableSection *section0 = (IGTestReorderableSection *)[self.adapter sectionControllerForSection:0];
+    IGTestReorderableSection *section1 = (IGTestReorderableSection *)[self.adapter sectionControllerForSection:1];
+    IGTestReorderableSection *section2 = (IGTestReorderableSection *)[self.adapter sectionControllerForSection:2];
+    section0.sectionObject = [IGTestReorderableSectionObject sectionWithObjects:@[@0]];
+    section0.isReorderable = YES;
+    section1.sectionObject = [IGTestReorderableSectionObject sectionWithObjects:@[@0]];
+    section2.sectionObject = [IGTestReorderableSectionObject sectionWithObjects:@[@0]];
+
+    [self.adapter performUpdatesAnimated:NO completion:nil];
+
+    NSIndexPath *fromIndexPath = [NSIndexPath indexPathForItem:0 inSection:0];
+    NSIndexPath *lastSpotIndexPath = [NSIndexPath indexPathForItem:1 inSection:2];
+    NSIndexPath *toIndexPath = [NSIndexPath indexPathForItem:1 inSection:1];
+
+    // move the first section item to the middle while simulating dragging to the last spot and back.
+    NSIndexPath *interpretedPath = [self interpretedIndexPathFromIndexPath:fromIndexPath toIndexPath:lastSpotIndexPath];
+    interpretedPath = [self interpretedIndexPathFromIndexPath:interpretedPath toIndexPath:toIndexPath];
+    [self.adapter collectionView:self.collectionView moveItemAtIndexPath:fromIndexPath toIndexPath:interpretedPath];
+
+    XCTAssertEqual(section0, [self.adapter sectionControllerForSection:1]);
+    XCTAssertEqual(section1, [self.adapter sectionControllerForSection:0]);
+    XCTAssertEqual(section2, [self.adapter sectionControllerForSection:2]);
+}
+
 @end