Layout invalidation API

CHANGELOG.md

@@ -30,6 +30,8 @@ This release closes the [3.0.0 milestone](https://github.com/Instagram/IGListKit
 
 - You can now manually move items (cells) within a section controller, ex: `[self.collectionContext moveInSectionController:self fromIndex:0 toIndex:1]`. [Ryan Nystrom](https://github.com/rnystrom) [(#418)](https://github.com/Instagram/IGListKit/pull/418)
 
+- Invalidate the layout of a section controller and control the transition with `UIView` animation APIs. [Ryan Nystrom](https://github.com/rnystrom) [(#499)](https://github.com/Instagram/IGListKit/pull/499)
+
 ### Fixes
 
 - Gracefully handle a `nil` section controller returned by an `IGListAdapterDataSource`. [Ryan Nystrom](https://github.com/rnystrom) [(tbd)](https://github.com/Instagram/IGListKit/pull/tbd)

Source/IGListAdapter.m

@@ -1105,7 +1105,7 @@ - (void)scrollToSectionController:(IGListSectionController<IGListSectionType> *)
 }
 
 - (void)invalidateLayoutForSectionController:(IGListSectionController<IGListSectionType> *)sectionController
-                                  completion:(void (^)(BOOL))completion{
+                                  completion:(void (^)(BOOL finished))completion{
     const NSInteger section = [self sectionForSectionController:sectionController];
     const NSInteger items = [_collectionView numberOfItemsInSection:section];
 

Source/IGListCollectionContext.h

@@ -228,7 +228,7 @@ NS_ASSUME_NONNULL_BEGIN
  without animations, or use springs.
  */
 - (void)invalidateLayoutForSectionController:(IGListSectionController<IGListSectionType> *)sectionController
-                                  completion:(nullable void (^)(BOOL))completion;
+                                  completion:(nullable void (^)(BOOL finished))completion;
 
 /**
  Batches and performs many cell-level updates in a single transaction.

Source/IGListStackedSectionController.m

@@ -311,6 +311,10 @@ - (void)scrollToSectionController:(IGListSectionController<IGListSectionType> *)
                                              animated:animated];
 }
 
+- (void)invalidateLayoutForSectionController:(IGListSectionController<IGListSectionType> *)sectionController completion:(void (^)(BOOL))completion {
+    [self.collectionContext invalidateLayoutForSectionController:self completion:completion];
+}
+
 #pragma mark - IGListDisplayDelegate
 
 - (void)listAdapter:(IGListAdapter *)listAdapter willDisplaySectionController:(IGListSectionController<IGListSectionType> *)sectionController cell:(UICollectionViewCell *)cell atIndex:(NSInteger)index {

Tests/IGListAdapterE2ETests.m

@@ -1337,4 +1337,32 @@ - (void)test_whenMovingItems_withNoBatchUpdate_thatCollectionViewWorks {
     XCTAssertEqualObjects(movedCell2.label.text, @"foo");
 }
 
+- (void)test_whenInvalidatingSectionController_withSizeChange_thatCellsAreSameInstance_thatCellsFrameChanged {
+    [self setupWithObjects:@[
+                             genTestObject(@1, @2),
+                             ]];
+
+    NSIndexPath *path1 = [NSIndexPath indexPathForItem:0 inSection:0];
+    NSIndexPath *path2 = [NSIndexPath indexPathForItem:1 inSection:0];
+    IGTestCell *cell1 = (IGTestCell*)[self.collectionView cellForItemAtIndexPath:path1];
+    IGTestCell *cell2 = (IGTestCell*)[self.collectionView cellForItemAtIndexPath:path2];
+
+    XCTAssertEqual(cell1.frame.size.height, 10);
+    XCTAssertEqual(cell2.frame.size.height, 10);
+
+    IGTestDelegateController *section = [self.adapter sectionControllerForObject:self.dataSource.objects.lastObject];
+    section.height = 20.0;
+
+    XCTestExpectation *expectation = genExpectation;
+    [section.collectionContext invalidateLayoutForSectionController:section completion:^(BOOL finished) {
+        XCTAssertEqual(cell1, [self.collectionView cellForItemAtIndexPath:path1]);
+        XCTAssertEqual(cell2, [self.collectionView cellForItemAtIndexPath:path2]);
+        XCTAssertEqual(cell1.frame.size.height, 20);
+        XCTAssertEqual(cell2.frame.size.height, 20);
+        [expectation fulfill];
+    }];
+
+    [self waitForExpectationsWithTimeout:15 handler:nil];
+}
+
 @end

Tests/Objects/IGTestDelegateController.h

@@ -17,6 +17,8 @@
 
 @property (nonatomic, strong, readonly) IGTestObject *item;
 
+@property (nonatomic, assign) CGFloat height;
+
 @property (nonatomic, copy) void (^itemUpdateBlock)();
 @property (nonatomic, copy) void (^cellConfigureBlock)(IGTestDelegateController *);
 @property (nonatomic, assign, readonly) NSInteger updateCount;

Tests/Objects/IGTestDelegateController.m

@@ -18,6 +18,7 @@ - (instancetype)init {
     if (self = [super init]) {
         _willDisplayCellIndexes = [NSCountedSet new];
         _didEndDisplayCellIndexes = [NSCountedSet new];
+        _height = 10.0;
         self.workingRangeDelegate = self;
     }
     return self;
@@ -31,7 +32,7 @@ - (NSInteger)numberOfItems {
 }
 
 - (CGSize)sizeForItemAtIndex:(NSInteger)index {
-    return CGSizeMake(self.collectionContext.containerSize.width, 10);
+    return CGSizeMake(self.collectionContext.containerSize.width, self.height);
 }
 
 - (UICollectionViewCell *)cellForItemAtIndex:(NSInteger)index {