Add support for keeping letting cell nodes update to new view models when reloaded. #trivial

AsyncDisplayKit.xcodeproj/project.pbxproj

@@ -326,6 +326,7 @@
 		CC11F97A1DB181180024D77B /* ASNetworkImageNodeTests.m in Sources */ = {isa = PBXBuildFile; fileRef = CC11F9791DB181180024D77B /* ASNetworkImageNodeTests.m */; };
 		CC2F65EE1E5FFB1600DA57C9 /* ASMutableElementMap.h in Headers */ = {isa = PBXBuildFile; fileRef = CC2F65EC1E5FFB1600DA57C9 /* ASMutableElementMap.h */; };
 		CC2F65EF1E5FFB1600DA57C9 /* ASMutableElementMap.m in Sources */ = {isa = PBXBuildFile; fileRef = CC2F65ED1E5FFB1600DA57C9 /* ASMutableElementMap.m */; };
+		CC311E071EEF81C400A8D7A6 /* ASDisplayNode+OCMock.m in Sources */ = {isa = PBXBuildFile; fileRef = CC311E061EEF81C400A8D7A6 /* ASDisplayNode+OCMock.m */; };
 		CC3B20841C3F76D600798563 /* ASPendingStateController.h in Headers */ = {isa = PBXBuildFile; fileRef = CC3B20811C3F76D600798563 /* ASPendingStateController.h */; settings = {ATTRIBUTES = (Private, ); }; };
 		CC3B20861C3F76D600798563 /* ASPendingStateController.mm in Sources */ = {isa = PBXBuildFile; fileRef = CC3B20821C3F76D600798563 /* ASPendingStateController.mm */; };
 		CC3B208A1C3F7A5400798563 /* ASWeakSet.h in Headers */ = {isa = PBXBuildFile; fileRef = CC3B20871C3F7A5400798563 /* ASWeakSet.h */; settings = {ATTRIBUTES = (Public, ); }; };
@@ -784,6 +785,7 @@
 		CC2E317F1DAC353700EEE891 /* ASCollectionView+Undeprecated.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = "ASCollectionView+Undeprecated.h"; sourceTree = "<group>"; };
 		CC2F65EC1E5FFB1600DA57C9 /* ASMutableElementMap.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = ASMutableElementMap.h; sourceTree = "<group>"; };
 		CC2F65ED1E5FFB1600DA57C9 /* ASMutableElementMap.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = ASMutableElementMap.m; sourceTree = "<group>"; };
+		CC311E061EEF81C400A8D7A6 /* ASDisplayNode+OCMock.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = "ASDisplayNode+OCMock.m"; sourceTree = "<group>"; };
 		CC3B20811C3F76D600798563 /* ASPendingStateController.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = ASPendingStateController.h; sourceTree = "<group>"; };
 		CC3B20821C3F76D600798563 /* ASPendingStateController.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; path = ASPendingStateController.mm; sourceTree = "<group>"; };
 		CC3B20871C3F7A5400798563 /* ASWeakSet.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = ASWeakSet.h; sourceTree = "<group>"; };
@@ -1117,6 +1119,7 @@
 		058D09C5195D04C000B7D73C /* Tests */ = {
 			isa = PBXGroup;
 			children = (
+				CC311E061EEF81C400A8D7A6 /* ASDisplayNode+OCMock.m */,
 				CCB338E51EEE27760081F21A /* ASTestCase.h */,
 				CCB338E61EEE27760081F21A /* ASTestCase.m */,
 				CCB338E21EEE11160081F21A /* OCMockObject+ASAdditions.h */,
@@ -2077,6 +2080,7 @@
 				058D0A3C195D057000B7D73C /* ASMutableAttributedStringBuilderTests.m in Sources */,
 				CC8B05D81D73979700F54286 /* ASTextNodePerformanceTests.m in Sources */,
 				697B315A1CFE4B410049936F /* ASEditableTextNodeTests.m in Sources */,
+				CC311E071EEF81C400A8D7A6 /* ASDisplayNode+OCMock.m in Sources */,
 				CCB338E41EEE11160081F21A /* OCMockObject+ASAdditions.m in Sources */,
 				ACF6ED611B178DC700DA7C62 /* ASOverlayLayoutSpecSnapshotTests.mm in Sources */,
 				CC8B05D61D73836400F54286 /* ASPerformanceTestContext.m in Sources */,

Source/ASCellNode.h

@@ -126,6 +126,13 @@ typedef NS_ENUM(NSUInteger, ASCellNodeVisibilityEvent) {
  */
 @property (atomic, nullable) id viewModel;
 
+/**
+ * Asks the node whether it can be updated to the given view model.
+ *
+ * The default implementation returns YES if the class matches that of the current view-model.
+ */
+- (BOOL)canUpdateToViewModel:(id)viewModel;
+
 /**
  * The backing view controller, or @c nil if the node wasn't initialized with backing view controller
  * @note This property must be accessed on the main thread.

Source/ASCellNode.mm

@@ -177,6 +177,11 @@ - (void)__setHighlightedFromUIKit:(BOOL)highlighted;
   }
 }
 
+- (BOOL)canUpdateToViewModel:(id)viewModel
+{
+  return [self.viewModel class] == [viewModel class];
+}
+
 - (NSIndexPath *)indexPath
 {
   return [self.owningNode indexPathForNode:self];

Source/Details/ASDataController.mm

@@ -303,6 +303,7 @@ - (void)_repopulateSupplementaryNodesIntoMap:(ASMutableElementMap *)map
                              traitCollection:(ASPrimitiveTraitCollection)traitCollection
                             indexPathsAreNew:(BOOL)indexPathsAreNew
                        shouldFetchSizeRanges:(BOOL)shouldFetchSizeRanges
+                                 previousMap:(ASElementMap *)previousMap
 {
   ASDisplayNodeAssertMainThread();
 
@@ -325,7 +326,7 @@ - (void)_repopulateSupplementaryNodesIntoMap:(ASMutableElementMap *)map
   }
 
   for (NSString *kind in [self supplementaryKindsInSections:newSections]) {
-    [self _insertElementsIntoMap:map kind:kind forSections:newSections traitCollection:traitCollection shouldFetchSizeRanges:shouldFetchSizeRanges];
+    [self _insertElementsIntoMap:map kind:kind forSections:newSections traitCollection:traitCollection shouldFetchSizeRanges:shouldFetchSizeRanges changeSet:changeSet previousMap:previousMap];
   }
 }
 
@@ -342,6 +343,8 @@ - (void)_insertElementsIntoMap:(ASMutableElementMap *)map
                    forSections:(NSIndexSet *)sections
                traitCollection:(ASPrimitiveTraitCollection)traitCollection
          shouldFetchSizeRanges:(BOOL)shouldFetchSizeRanges
+                     changeSet:(_ASHierarchyChangeSet *)changeSet
+                   previousMap:(ASElementMap *)previousMap
 {
   ASDisplayNodeAssertMainThread();
 
@@ -350,7 +353,7 @@ - (void)_insertElementsIntoMap:(ASMutableElementMap *)map
   }
 
   NSArray<NSIndexPath *> *indexPaths = [self _allIndexPathsForItemsOfKind:kind inSections:sections];
-  [self _insertElementsIntoMap:map kind:kind atIndexPaths:indexPaths traitCollection:traitCollection shouldFetchSizeRanges:shouldFetchSizeRanges];
+  [self _insertElementsIntoMap:map kind:kind atIndexPaths:indexPaths traitCollection:traitCollection shouldFetchSizeRanges:shouldFetchSizeRanges changeSet:changeSet previousMap:previousMap];
 }
 
 /**
@@ -367,6 +370,8 @@ - (void)_insertElementsIntoMap:(ASMutableElementMap *)map
                   atIndexPaths:(NSArray<NSIndexPath *> *)indexPaths
                traitCollection:(ASPrimitiveTraitCollection)traitCollection
          shouldFetchSizeRanges:(BOOL)shouldFetchSizeRanges
+                     changeSet:(_ASHierarchyChangeSet *)changeSet
+                   previousMap:(ASElementMap *)previousMap
 {
   ASDisplayNodeAssertMainThread();
 
@@ -384,11 +389,28 @@ - (void)_insertElementsIntoMap:(ASMutableElementMap *)map
   id<ASDataControllerSource> dataSource = self.dataSource;
   id<ASRangeManagingNode> node = self.node;
   for (NSIndexPath *indexPath in indexPaths) {
-    id viewModel = [dataSource dataController:self viewModelForItemAtIndexPath:indexPath];
-
     ASCellNodeBlock nodeBlock;
+    id viewModel;
     if (isRowKind) {
-      nodeBlock = [dataSource dataController:self nodeBlockAtIndexPath:indexPath];
+      viewModel = [dataSource dataController:self viewModelForItemAtIndexPath:indexPath];
+
+      // Get the prior element and attempt to update the existing cell node.
+      if (viewModel != nil && !changeSet.includesReloadData) {
+        NSIndexPath *oldIndexPath = [changeSet oldIndexPathForNewIndexPath:indexPath];
+        if (oldIndexPath != nil) {
+          ASCollectionElement *oldElement = [previousMap elementForItemAtIndexPath:oldIndexPath];
+          ASCellNode *oldNode = oldElement.node;
+          if ([oldNode canUpdateToViewModel:viewModel]) {
+            // Just wrap the node in a block. The collection element will -setViewModel:
+            nodeBlock = ^{
+              return oldNode;
+            };
+          }
+        }
+      }
+      if (nodeBlock == nil) {
+        nodeBlock = [dataSource dataController:self nodeBlockAtIndexPath:indexPath];
+      }
     } else {
       nodeBlock = [dataSource dataController:self supplementaryNodeBlockOfKind:kind atIndexPath:indexPath];
     }
@@ -534,14 +556,15 @@ - (void)updateWithChangeSet:(_ASHierarchyChangeSet *)changeSet
   }
 
   // Mutable copy of current data.
-  ASMutableElementMap *mutableMap = [_pendingMap mutableCopy];
+  ASElementMap *previousMap = _pendingMap;
+  ASMutableElementMap *mutableMap = [previousMap mutableCopy];
 
   BOOL canDelegateLayout = (_layoutDelegate != nil);
 
   // Step 1: Update the mutable copies to match the data source's state
   [self _updateSectionContextsInMap:mutableMap changeSet:changeSet];
   ASPrimitiveTraitCollection existingTraitCollection = [self.node primitiveTraitCollection];
-  [self _updateElementsInMap:mutableMap changeSet:changeSet traitCollection:existingTraitCollection shouldFetchSizeRanges:(! canDelegateLayout)];
+  [self _updateElementsInMap:mutableMap changeSet:changeSet traitCollection:existingTraitCollection shouldFetchSizeRanges:(! canDelegateLayout) previousMap:previousMap];
 
   // Step 2: Clone the new data
   ASElementMap *newMap = [mutableMap copy];
@@ -644,6 +667,7 @@ - (void)_updateElementsInMap:(ASMutableElementMap *)map
                    changeSet:(_ASHierarchyChangeSet *)changeSet
              traitCollection:(ASPrimitiveTraitCollection)traitCollection
        shouldFetchSizeRanges:(BOOL)shouldFetchSizeRanges
+                 previousMap:(ASElementMap *)previousMap
 {
   ASDisplayNodeAssertMainThread();
 
@@ -653,7 +677,7 @@ - (void)_updateElementsInMap:(ASMutableElementMap *)map
     NSUInteger sectionCount = [self itemCountsFromDataSource].size();
     if (sectionCount > 0) {
       NSIndexSet *sectionIndexes = [NSIndexSet indexSetWithIndexesInRange:NSMakeRange(0, sectionCount)];
-      [self _insertElementsIntoMap:map sections:sectionIndexes traitCollection:traitCollection shouldFetchSizeRanges:shouldFetchSizeRanges];
+      [self _insertElementsIntoMap:map sections:sectionIndexes traitCollection:traitCollection shouldFetchSizeRanges:shouldFetchSizeRanges changeSet:changeSet previousMap:previousMap];
     }
     // Return immediately because reloadData can't be used in conjuntion with other updates.
     return;
@@ -666,7 +690,8 @@ - (void)_updateElementsInMap:(ASMutableElementMap *)map
                                      changeSet:changeSet
                                traitCollection:traitCollection
                               indexPathsAreNew:NO
-                         shouldFetchSizeRanges:shouldFetchSizeRanges];
+                         shouldFetchSizeRanges:shouldFetchSizeRanges
+                                   previousMap:previousMap];
   }
 
   for (_ASHierarchySectionChange *change in [changeSet sectionChangesOfType:_ASHierarchyChangeTypeDelete]) {
@@ -676,24 +701,27 @@ - (void)_updateElementsInMap:(ASMutableElementMap *)map
   }
 
   for (_ASHierarchySectionChange *change in [changeSet sectionChangesOfType:_ASHierarchyChangeTypeInsert]) {
-    [self _insertElementsIntoMap:map sections:change.indexSet traitCollection:traitCollection shouldFetchSizeRanges:shouldFetchSizeRanges];
+    [self _insertElementsIntoMap:map sections:change.indexSet traitCollection:traitCollection shouldFetchSizeRanges:shouldFetchSizeRanges changeSet:changeSet previousMap:previousMap];
   }
 
   for (_ASHierarchyItemChange *change in [changeSet itemChangesOfType:_ASHierarchyChangeTypeInsert]) {
-    [self _insertElementsIntoMap:map kind:ASDataControllerRowNodeKind atIndexPaths:change.indexPaths traitCollection:traitCollection shouldFetchSizeRanges:shouldFetchSizeRanges];
+    [self _insertElementsIntoMap:map kind:ASDataControllerRowNodeKind atIndexPaths:change.indexPaths traitCollection:traitCollection shouldFetchSizeRanges:shouldFetchSizeRanges changeSet:changeSet previousMap:previousMap];
     // Aggressively reload supplementary nodes (#1773 & #1629)
     [self _repopulateSupplementaryNodesIntoMap:map forSectionsContainingIndexPaths:change.indexPaths
                                      changeSet:changeSet
                                traitCollection:traitCollection
                               indexPathsAreNew:YES
-                         shouldFetchSizeRanges:shouldFetchSizeRanges];
+                         shouldFetchSizeRanges:shouldFetchSizeRanges
+                                   previousMap:previousMap];
   }
 }
 
 - (void)_insertElementsIntoMap:(ASMutableElementMap *)map
                       sections:(NSIndexSet *)sectionIndexes
                traitCollection:(ASPrimitiveTraitCollection)traitCollection
          shouldFetchSizeRanges:(BOOL)shouldFetchSizeRanges
+                     changeSet:(_ASHierarchyChangeSet *)changeSet
+                   previousMap:(ASElementMap *)previousMap
 {
   ASDisplayNodeAssertMainThread();
 
@@ -703,12 +731,12 @@ - (void)_insertElementsIntoMap:(ASMutableElementMap *)map
 
   // Items
   [map insertEmptySectionsOfItemsAtIndexes:sectionIndexes];
-  [self _insertElementsIntoMap:map kind:ASDataControllerRowNodeKind forSections:sectionIndexes traitCollection:traitCollection shouldFetchSizeRanges:shouldFetchSizeRanges];
+  [self _insertElementsIntoMap:map kind:ASDataControllerRowNodeKind forSections:sectionIndexes traitCollection:traitCollection shouldFetchSizeRanges:shouldFetchSizeRanges changeSet:changeSet previousMap:previousMap];
 
   // Supplementaries
   for (NSString *kind in [self supplementaryKindsInSections:sectionIndexes]) {
     // Step 2: Populate new elements for all sections
-    [self _insertElementsIntoMap:map kind:kind forSections:sectionIndexes traitCollection:traitCollection shouldFetchSizeRanges:shouldFetchSizeRanges];
+    [self _insertElementsIntoMap:map kind:kind forSections:sectionIndexes traitCollection:traitCollection shouldFetchSizeRanges:shouldFetchSizeRanges changeSet:changeSet previousMap:previousMap];
   }
 }
 

Source/Private/_ASHierarchyChangeSet.h

@@ -147,6 +147,14 @@ NSString *NSStringFromASHierarchyChangeType(_ASHierarchyChangeType changeType);
  */
 - (NSUInteger)newSectionForOldSection:(NSUInteger)oldSection;
 
+/**
+ * Get the old item index path for the given new index path.
+ *
+ * @precondition The change set must be completed.
+ * @return The old index path, or nil if the given item was inserted.
+ */
+- (nullable NSIndexPath *)oldIndexPathForNewIndexPath:(NSIndexPath *)indexPath;
+
 /// Call this once the change set has been constructed to prevent future modifications to the changeset. Calling this more than once is a programmer error.
 /// NOTE: Calling this method will cause the changeset to convert all reloads into delete/insert pairs.
 - (void)markCompletedWithNewItemCounts:(std::vector<NSInteger>)newItemCounts;

Source/Private/_ASHierarchyChangeSet.mm

@@ -1,5 +1,5 @@
 //
-//  _ASHierarchyChangeSet.m
+//  _ASHierarchyChangeSet.mm
 //  Texture
 //
 //  Copyright (c) 2014-present, Facebook, Inc.  All rights reserved.
@@ -256,6 +256,45 @@ - (NSUInteger)newSectionForOldSection:(NSUInteger)oldSection
   return newIndex;
 }
 
+- (NSUInteger)oldSectionForNewSection:(NSUInteger)newSection
+{
+  [self _ensureCompleted];
+  if ([_insertedSections containsIndex:newSection]) {
+    return NSNotFound;
+  }
+
+  NSInteger oldIndex = newSection - [_insertedSections as_indexChangeByInsertingItemsBelowIndex:newSection];
+  oldIndex += [_deletedSections countOfIndexesInRange:NSMakeRange(0, oldIndex)];
+  return oldIndex;
+}
+
+- (NSIndexPath *)oldIndexPathForNewIndexPath:(NSIndexPath *)indexPath
+{
+  [self _ensureCompleted];
+  // Inserted sections return nil.
+  NSInteger newSection = indexPath.section;
+  NSInteger newItem = indexPath.item;
+  NSInteger oldSection = [self oldSectionForNewSection:newSection];
+  if (oldSection == NSNotFound) {
+    return nil;
+  }
+
+  // Inserted items return nil.
+  for (_ASHierarchyItemChange *change in _originalInsertItemChanges) {
+    if ([change.indexPaths containsObject:indexPath]) {
+      return nil;
+    }
+  }
+
+  // TODO: This is a pretty inefficient way to do this.
+  NSIndexSet *insertsInSection = [_ASHierarchyItemChange sectionToIndexSetMapFromChanges:_insertItemChanges][@(newSection)];
+  NSIndexSet *deletesInSection = [_ASHierarchyItemChange sectionToIndexSetMapFromChanges:_deleteItemChanges][@(oldSection)];
+
+  NSInteger oldIndex = newItem - [insertsInSection as_indexChangeByInsertingItemsBelowIndex:newItem];
+  oldIndex += [deletesInSection countOfIndexesInRange:NSMakeRange(0, oldIndex)];
+  return [NSIndexPath indexPathForItem:oldIndex inSection:oldSection];
+}
+
 - (void)reloadData
 {
   [self _ensureNotCompleted];