Merge commit 'ba08ae1318cac3a40c4c0fe6c920e1675117dc2f'

AsyncDisplayKit.xcodeproj/project.pbxproj

@@ -425,6 +425,7 @@
 		DECBD6EA1BE56E1900CF4905 /* ASButtonNode.mm in Sources */ = {isa = PBXBuildFile; fileRef = DECBD6E61BE56E1900CF4905 /* ASButtonNode.mm */; };
 		DEFAD8131CC48914000527C4 /* ASVideoNode.mm in Sources */ = {isa = PBXBuildFile; fileRef = AEEC47E01C20C2DD00EC1693 /* ASVideoNode.mm */; };
 		E51B78BF1F028ABF00E32604 /* ASLayoutFlatteningTests.m in Sources */ = {isa = PBXBuildFile; fileRef = E51B78BD1F01A0EE00E32604 /* ASLayoutFlatteningTests.m */; };
+		E54E00721F1D3828000B30D7 /* ASPagerNode+Beta.h in Headers */ = {isa = PBXBuildFile; fileRef = E54E00711F1D3828000B30D7 /* ASPagerNode+Beta.h */; settings = {ATTRIBUTES = (Public, ); }; };
 		E54E81FC1EB357BD00FFE8E1 /* ASPageTable.h in Headers */ = {isa = PBXBuildFile; fileRef = E54E81FA1EB357BD00FFE8E1 /* ASPageTable.h */; };
 		E54E81FD1EB357BD00FFE8E1 /* ASPageTable.m in Sources */ = {isa = PBXBuildFile; fileRef = E54E81FB1EB357BD00FFE8E1 /* ASPageTable.m */; };
 		E55D86331CA8A14000A0C26F /* ASLayoutElement.mm in Sources */ = {isa = PBXBuildFile; fileRef = E55D86311CA8A14000A0C26F /* ASLayoutElement.mm */; };
@@ -912,6 +913,7 @@
 		E51B78BD1F01A0EE00E32604 /* ASLayoutFlatteningTests.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = ASLayoutFlatteningTests.m; sourceTree = "<group>"; };
 		E52405B21C8FEF03004DC8E7 /* ASLayoutTransition.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; path = ASLayoutTransition.mm; sourceTree = "<group>"; };
 		E52405B41C8FEF16004DC8E7 /* ASLayoutTransition.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = ASLayoutTransition.h; sourceTree = "<group>"; };
+		E54E00711F1D3828000B30D7 /* ASPagerNode+Beta.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = "ASPagerNode+Beta.h"; sourceTree = "<group>"; };
 		E54E81FA1EB357BD00FFE8E1 /* ASPageTable.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = ASPageTable.h; sourceTree = "<group>"; };
 		E54E81FB1EB357BD00FFE8E1 /* ASPageTable.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = ASPageTable.m; sourceTree = "<group>"; };
 		E55D86311CA8A14000A0C26F /* ASLayoutElement.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; path = ASLayoutElement.mm; sourceTree = "<group>"; };
@@ -1101,6 +1103,7 @@
 				698371DA1E4379CD00437585 /* ASNodeController+Beta.m */,
 				25E327541C16819500A2170C /* ASPagerNode.h */,
 				25E327551C16819500A2170C /* ASPagerNode.m */,
+				E54E00711F1D3828000B30D7 /* ASPagerNode+Beta.h */,
 				A2763D771CBDD57D00A9ADBD /* ASPINRemoteImageDownloader.h */,
 				A2763D781CBDD57D00A9ADBD /* ASPINRemoteImageDownloader.m */,
 				CCBBBF5C1EB161760069AA91 /* ASRangeManagingNode.h */,
@@ -1708,6 +1711,7 @@
 			isa = PBXHeadersBuildPhase;
 			buildActionMask = 2147483647;
 			files = (
+				E54E00721F1D3828000B30D7 /* ASPagerNode+Beta.h in Headers */,
 				E5B225281F1790D6001E1431 /* ASHashing.h in Headers */,
 				CC034A131E649F1300626263 /* AsyncDisplayKit+IGListKitMethods.h in Headers */,
 				693A1DCA1ECC944E00D0C9D2 /* IGListAdapter+AsyncDisplayKit.h in Headers */,

CHANGELOG.md

@@ -1,9 +1,16 @@
 ## master
 
 * Add your own contributions to the next release on the line below this with your name.
+- [ASStackLayoutSpec] Add lineSpacing property working with flex wrap. [Flo Vouin](https://github.com/flovouin)
+- [ASStackLayoutSpec] Fix flex wrap overflow in some cases using item spacing. [Flo Vouin](https://github.com/flovouin)
+- [ASNodeController] Add -nodeDidLayout callback. Allow switching retain behavior at runtime. [Scott Goodson](https://github.com/appleguy)
+- [ASCollectionView] Add delegate bridging and index space translation for missing UICollectionViewLayout properties. [Scott Goodson](https://github.com/appleguy)
 - [ASTextNode2] Add initial implementation for link handling. [Scott Goodson](https://github.com/appleguy) [#396](https://github.com/TextureGroup/Texture/pull/396)
 - [ASTextNode2] Provide compile flag to globally enable new implementation of ASTextNode: ASTEXTNODE_EXPERIMENT_GLOBAL_ENABLE. [Scott Goodson](https://github.com/appleguy) [#396](https://github.com/TextureGroup/Texture/pull/410)
- - Add ASCollectionGalleryLayoutDelegate - an async collection layout that makes same-size collections (e.g photo galleries, pagers, etc) fast and lightweight! [Huy Nguyen](https://github.com/nguyenhuy/) [#76](https://github.com/TextureGroup/Texture/pull/76)
+- Add ASCollectionGalleryLayoutDelegate - an async collection layout that makes same-size collections (e.g photo galleries, pagers, etc) fast and lightweight! [Huy Nguyen](https://github.com/nguyenhuy/) [#76](https://github.com/TextureGroup/Texture/pull/76) [#451](https://github.com/TextureGroup/Texture/pull/451)
+- Fix an issue that causes infinite layout loop in ASDisplayNode after [#428](https://github.com/TextureGroup/Texture/pull/428) [Huy Nguyen](https://github.com/nguyenhuy) [#455](https://github.com/TextureGroup/Texture/pull/455) 
+- Fix an issue in layout transition that causes it to unexpectedly use the old layout [Huy Nguyen](https://github.com/nguyenhuy) [#464](https://github.com/TextureGroup/Texture/pull/464)
+- Add -[ASDisplayNode detailedLayoutDescription] property to aid debugging. [Adlai Holler](https://github.com/Adlai-Holler) [#476](https://github.com/TextureGroup/Texture/pull/476)
 
 ##2.3.5
 - Fix an issue where inserting/deleting sections could lead to inconsistent supplementary element behavior. [Adlai Holler](https://github.com/Adlai-Holler)
@@ -11,6 +18,7 @@
 - Fix a crash where scrolling a table view after entering editing mode could lead to bad internal states in the table. [Huy Nguyen](https://github.com/nguyenhuy) [#416](https://github.com/TextureGroup/Texture/pull/416/)
 - Fix a crash in collection view that occurs if batch updates are performed while scrolling [Huy Nguyen](https://github.com/nguyenhuy) [#378](https://github.com/TextureGroup/Texture/issues/378)
 - Some improvements in ASCollectionView [Huy Nguyen](https://github.com/nguyenhuy) [#407](https://github.com/TextureGroup/Texture/pull/407)
+- Small refactors in ASDataController [Huy Nguyen](https://github.com/TextureGroup/Texture/pull/443) [#443](https://github.com/TextureGroup/Texture/pull/443)
 
 ##2.3.4
 - [Yoga] Rewrite YOGA_TREE_CONTIGUOUS mode with improved behavior and cleaner integration [Scott Goodson](https://github.com/appleguy)

Source/ASCellNode.h

@@ -89,7 +89,6 @@ typedef NS_ENUM(NSUInteger, ASCellNodeVisibilityEvent) {
  *
  * @return The supplementary element kind, or @c nil if this node does not represent a supplementary element.
  */
-//TODO change this to be a generic "kind" or "elementKind" that exposes `nil` for row kind
 @property (atomic, copy, readonly, nullable) NSString *supplementaryElementKind;
 
 /*

Source/ASCollectionNode.mm

@@ -218,8 +218,10 @@
   // Intentionally allocate the view here and trigger a layout pass on it, which in turn will trigger the intial data load.
   // We can get rid of this call later when ASDataController, ASRangeController and ASCollectionLayout can operate without the view.
   // TODO (ASCL) If this node supports async layout, kick off the initial data load without allocating the view
+  if (CGRectEqualToRect(self.bounds, CGRectZero) == NO) {
     [[self view] layoutIfNeeded];
   }
+}
 
 #if ASRangeControllerLoggingEnabled
 - (void)didEnterVisibleState

Source/ASCollectionView.mm

@@ -622,15 +622,17 @@ static NSString * const kReuseIdentifier = @"_ASCollectionReuseIdentifier";
     return CGSizeZero;
   }
 
-  NSString *supplementaryKind = element.supplementaryElementKind;
+  ASCellNode *node = element.node;
-  NSIndexPath *indexPath = [_dataController.visibleMap indexPathForElement:element];
+  BOOL useUIKitCell = node.shouldUseUIKitCell;
-  ASSizeRange sizeRange;
+  if (useUIKitCell) {
-  if (supplementaryKind == nil) {
+    // In this case, we should use the exact value that was stashed earlier by calling sizeForItem:, referenceSizeFor*, etc.
-    sizeRange = [self dataController:_dataController constrainedSizeForNodeAtIndexPath:indexPath];
+    // Although the node would use the preferredSize in layoutThatFits, we can skip this because there's no constrainedSize.
+    ASDisplayNodeAssert([node.superclass isSubclassOfClass:[ASCellNode class]] == NO,
+                        @"Placeholder cells for UIKit passthrough should be generic ASCellNodes: %@", node);
+    return node.style.preferredSize;
   } else {
-    sizeRange = [self dataController:_dataController constrainedSizeForSupplementaryNodeOfKind:supplementaryKind atIndexPath:indexPath];
+    return [node layoutThatFits:element.constrainedSize].size;
   }
-  return [element.node layoutThatFits:sizeRange].size;
 }
 
 - (CGSize)calculatedSizeForNodeAtIndexPath:(NSIndexPath *)indexPath
@@ -949,63 +951,84 @@ static NSString * const kReuseIdentifier = @"_ASCollectionReuseIdentifier";
   return [_dataController.visibleMap numberOfItemsInSection:section];
 }
 
-- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath
+#define ASIndexPathForSection(section) [NSIndexPath indexPathForItem:0 inSection:section]
+#define ASFlowLayoutDefault(layout, property, default)                                        \
+({                                                                                            \
+  UICollectionViewFlowLayout *flowLayout = ASDynamicCast(layout, UICollectionViewFlowLayout); \
+  flowLayout ? flowLayout.property : default;                                                 \
+})
+
+- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)layout
+  sizeForItemAtIndexPath:(NSIndexPath *)indexPath
 {
   ASDisplayNodeAssertMainThread();
-  ASCollectionElement *element = [_dataController.visibleMap elementForItemAtIndexPath:indexPath];
+  ASCollectionElement *e = [_dataController.visibleMap elementForItemAtIndexPath:indexPath];
-  if (element == nil) {
+  return e ? [self sizeForElement:e] : ASFlowLayoutDefault(layout, itemSize, CGSizeZero);
-    ASDisplayNodeAssert(NO, @"Unexpected nil element for collectionView:layout:sizeForItemAtIndexPath: %@, %@, %@", self, collectionViewLayout, indexPath);
-    return CGSizeZero;
 }
 
-  ASCellNode *cell = element.node;
+- (CGSize)collectionView:(UICollectionView *)cv layout:(UICollectionViewLayout *)l
-  if (cell.shouldUseUIKitCell) {
+referenceSizeForHeaderInSection:(NSInteger)section
-    if ([_asyncDelegate respondsToSelector:@selector(collectionView:layout:sizeForItemAtIndexPath:)]) {
-      CGSize size = [(id)_asyncDelegate collectionView:collectionView layout:collectionViewLayout sizeForItemAtIndexPath:indexPath];
-      cell.style.preferredSize = size;
-      return size;
-    }
-  }
-
-  return [self sizeForElement:element];
-}
-
-- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)layout referenceSizeForHeaderInSection:(NSInteger)section
 {
   ASDisplayNodeAssertMainThread();
-  NSIndexPath *indexPath = [NSIndexPath indexPathForItem:0 inSection:section];
+  ASElementMap *map = _dataController.visibleMap;
-  ASCollectionElement *element = [_dataController.visibleMap supplementaryElementOfKind:UICollectionElementKindSectionHeader
+  ASCollectionElement *e = [map supplementaryElementOfKind:UICollectionElementKindSectionHeader
-                                                                            atIndexPath:indexPath];
+                                               atIndexPath:ASIndexPathForSection(section)];
-  if (element == nil) {
+  return e ? [self sizeForElement:e] : ASFlowLayoutDefault(l, headerReferenceSize, CGSizeZero);
-    return CGSizeZero;
 }
 
-  if (element.node.shouldUseUIKitCell && _asyncDelegateFlags.interop) {
+- (CGSize)collectionView:(UICollectionView *)cv layout:(UICollectionViewLayout *)l
-    if ([_asyncDelegate respondsToSelector:@selector(collectionView:layout:referenceSizeForHeaderInSection:)]) {
+referenceSizeForFooterInSection:(NSInteger)section
-      return [(id)_asyncDelegate collectionView:collectionView layout:layout referenceSizeForHeaderInSection:section];
-    }
-  }
-
-  return [self sizeForElement:element];
-}
-
-- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)layout referenceSizeForFooterInSection:(NSInteger)section
 {
   ASDisplayNodeAssertMainThread();
-  NSIndexPath *indexPath = [NSIndexPath indexPathForItem:0 inSection:section];
+  ASElementMap *map = _dataController.visibleMap;
-  ASCollectionElement *element = [_dataController.visibleMap supplementaryElementOfKind:UICollectionElementKindSectionFooter
+  ASCollectionElement *e = [map supplementaryElementOfKind:UICollectionElementKindSectionFooter
-                                                                            atIndexPath:indexPath];
+                                               atIndexPath:ASIndexPathForSection(section)];
-  if (element == nil) {
+  return e ? [self sizeForElement:e] : ASFlowLayoutDefault(l, footerReferenceSize, CGSizeZero);
-    return CGSizeZero;
 }
 
-  if (element.node.shouldUseUIKitCell && _asyncDelegateFlags.interop) {
+// For the methods that call delegateIndexPathForSection:withSelector:, translate the section from
-    if ([_asyncDelegate respondsToSelector:@selector(collectionView:layout:referenceSizeForFooterInSection:)]) {
+// visibleMap to pendingMap. If the section no longer exists, or the delegate doesn't implement
-      return [(id)_asyncDelegate collectionView:collectionView layout:layout referenceSizeForFooterInSection:section];
+// the selector, we will return a nil indexPath (and then use the ASFlowLayoutDefault).
+- (NSIndexPath *)delegateIndexPathForSection:(NSInteger)section withSelector:(SEL)selector
+{
+  if ([_asyncDelegate respondsToSelector:selector]) {
+    return [_dataController.pendingMap convertIndexPath:ASIndexPathForSection(section)
+                                                fromMap:_dataController.visibleMap];
+  } else {
+    return nil;
   }
 }
 
-  return [self sizeForElement:element];
+- (UIEdgeInsets)collectionView:(UICollectionView *)cv layout:(UICollectionViewLayout *)l
+        insetForSectionAtIndex:(NSInteger)section
+{
+  NSIndexPath *indexPath = [self delegateIndexPathForSection:section withSelector:_cmd];
+  if (indexPath) {
+    return [(id)_asyncDelegate collectionView:cv layout:l insetForSectionAtIndex:indexPath.section];
+  }
+  return ASFlowLayoutDefault(l, sectionInset, UIEdgeInsetsZero);
+}
+
+- (CGFloat)collectionView:(UICollectionView *)cv layout:(UICollectionViewLayout *)l
+minimumInteritemSpacingForSectionAtIndex:(NSInteger)section
+{
+  NSIndexPath *indexPath = [self delegateIndexPathForSection:section withSelector:_cmd];
+  if (indexPath) {
+    return [(id)_asyncDelegate collectionView:cv layout:l
+     minimumInteritemSpacingForSectionAtIndex:indexPath.section];
+  }
+  return ASFlowLayoutDefault(l, minimumInteritemSpacing, 10.0); // Default is documented as 10.0
+}
+
+- (CGFloat)collectionView:(UICollectionView *)cv layout:(UICollectionViewLayout *)l
+minimumLineSpacingForSectionAtIndex:(NSInteger)section
+{
+  NSIndexPath *indexPath = [self delegateIndexPathForSection:section withSelector:_cmd];
+  if (indexPath) {
+    return [(id)_asyncDelegate collectionView:cv layout:l
+          minimumLineSpacingForSectionAtIndex:indexPath.section];
+  }
+  return ASFlowLayoutDefault(l, minimumLineSpacing, 10.0);      // Default is documented as 10.0
 }
 
 - (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath
@@ -1678,11 +1701,19 @@ static NSString * const kReuseIdentifier = @"_ASCollectionReuseIdentifier";
 
   if (block == nil) {
     if (_asyncDataSourceFlags.interop) {
+      UICollectionViewLayout *layout = self.collectionViewLayout;
+      CGSize preferredSize = CGSizeZero;
+      SEL sizeForItem = @selector(collectionView:layout:sizeForItemAtIndexPath:);
+      if ([_asyncDelegate respondsToSelector:sizeForItem]) {
+        preferredSize = [(id)_asyncDelegate collectionView:self layout:layout sizeForItemAtIndexPath:indexPath];
+      } else {
+        preferredSize = ASFlowLayoutDefault(layout, itemSize, CGSizeZero);
+      }
       block = ^{
-        ASCellNode *cell = [[ASCellNode alloc] init];
+        ASCellNode *node = [[ASCellNode alloc] init];
-        cell.shouldUseUIKitCell = YES;
+        node.shouldUseUIKitCell = YES;
-        cell.style.preferredSize = CGSizeZero;
+        node.style.preferredSize = preferredSize;
-        return cell;
+        return node;
       };
     } else {
       ASDisplayNodeFailAssert(@"ASCollection could not get a node block for item at index path %@: %@, %@. If you are trying to display a UICollectionViewCell, make sure your dataSource conforms to the <ASCollectionDataSourceInterop> protocol!", indexPath, cell, block);
@@ -1773,9 +1804,31 @@ static NSString * const kReuseIdentifier = @"_ASCollectionReuseIdentifier";
       nodeBlock = ^{ return node; };
     } else {
       BOOL useUIKitCell = _asyncDataSourceFlags.interop;
+      CGSize preferredSize = CGSizeZero;
+      if (useUIKitCell) {
+        UICollectionViewLayout *layout = self.collectionViewLayout;
+        if ([kind isEqualToString:UICollectionElementKindSectionHeader]) {
+          SEL sizeForHeader = @selector(collectionView:layout:referenceSizeForHeaderInSection:);
+          if ([_asyncDelegate respondsToSelector:sizeForHeader]) {
+            preferredSize = [(id)_asyncDelegate collectionView:self layout:layout
+                               referenceSizeForHeaderInSection:indexPath.section];
+          } else {
+            preferredSize = ASFlowLayoutDefault(layout, headerReferenceSize, CGSizeZero);
+          }
+        } else if ([kind isEqualToString:UICollectionElementKindSectionFooter]) {
+          SEL sizeForFooter = @selector(collectionView:layout:referenceSizeForFooterInSection:);
+          if ([_asyncDelegate respondsToSelector:sizeForFooter]) {
+            preferredSize = [(id)_asyncDelegate collectionView:self layout:layout
+                               referenceSizeForFooterInSection:indexPath.section];
+          } else {
+            preferredSize = ASFlowLayoutDefault(layout, footerReferenceSize, CGSizeZero);
+          }
+        }
+      }
       nodeBlock = ^{
         ASCellNode *node = [[ASCellNode alloc] init];
         node.shouldUseUIKitCell = useUIKitCell;
+        node.style.preferredSize = preferredSize;
         return node;
       };
     }
@@ -1901,19 +1954,16 @@ static NSString * const kReuseIdentifier = @"_ASCollectionReuseIdentifier";
 
 #pragma mark - ASRangeControllerDelegate
 
-- (void)rangeController:(ASRangeController *)rangeController willUpdateWithChangeSet:(_ASHierarchyChangeSet *)changeSet
+- (void)rangeController:(ASRangeController *)rangeController updateWithChangeSet:(_ASHierarchyChangeSet *)changeSet updates:(dispatch_block_t)updates
 {
   ASDisplayNodeAssertMainThread();
-  
   if (!self.asyncDataSource || _superIsPendingDataLoad) {
+    updates();
+    [changeSet executeCompletionHandlerWithFinished:NO];
     return; // if the asyncDataSource has become invalid while we are processing, ignore this request to avoid crashes
   }
 
-  if (changeSet.includesReloadData) {
+  //TODO Do we need to notify _layoutFacilitator before reloadData?
-    //TODO Do we need to notify _layoutFacilitator?
-    return;
-  }
-  
   for (_ASHierarchyItemChange *change in [changeSet itemChangesOfType:_ASHierarchyChangeTypeDelete]) {
     [_layoutFacilitator collectionViewWillEditCellsAtIndexPaths:change.indexPaths batched:YES];
   }
@@ -1929,16 +1979,6 @@ static NSString * const kReuseIdentifier = @"_ASCollectionReuseIdentifier";
   for (_ASHierarchyItemChange *change in [changeSet itemChangesOfType:_ASHierarchyChangeTypeInsert]) {
     [_layoutFacilitator collectionViewWillEditCellsAtIndexPaths:change.indexPaths batched:YES];
   }
-}
-
-- (void)rangeController:(ASRangeController *)rangeController didUpdateWithChangeSet:(_ASHierarchyChangeSet *)changeSet updates:(dispatch_block_t)updates
-{
-  ASDisplayNodeAssertMainThread();
-  if (!self.asyncDataSource || _superIsPendingDataLoad) {
-    updates();
-    [changeSet executeCompletionHandlerWithFinished:NO];
-    return; // if the asyncDataSource has become invalid while we are processing, ignore this request to avoid crashes
-  }
 
   ASPerformBlockWithoutAnimation(!changeSet.animated, ^{
     as_activity_scope(as_activity_create("Commit collection update", changeSet.rootActivity, OS_ACTIVITY_FLAG_DEFAULT));

Source/ASDisplayNode+Layout.mm

@@ -185,6 +185,11 @@ ASPrimitiveTraitCollectionDeprecatedImplementation
 - (ASSizeRange)constrainedSizeForCalculatedLayout
 {
   ASDN::MutexLocker l(__instanceLock__);
+  return [self _locked_constrainedSizeForCalculatedLayout];
+}
+
+- (ASSizeRange)_locked_constrainedSizeForCalculatedLayout
+{
   if (_pendingDisplayNodeLayout != nullptr) {
     return _pendingDisplayNodeLayout->constrainedSize;
   }
@@ -305,7 +310,7 @@ ASPrimitiveTraitCollectionDeprecatedImplementation
 
   // Prefer _pendingDisplayNodeLayout over _calculatedDisplayNodeLayout (if exists, it's the newest)
   // If there is no _pending, check if _calculated is valid to reuse (avoiding recalculation below).
-  if (_pendingDisplayNodeLayout == nullptr) {
+  if (_pendingDisplayNodeLayout == nullptr || _pendingDisplayNodeLayout->version < _layoutVersion) {
     if (_calculatedDisplayNodeLayout->version >= _layoutVersion
         && (_calculatedDisplayNodeLayout->requestedLayoutFromAbove == YES
             || CGSizeEqualToSize(_calculatedDisplayNodeLayout->layout.size, boundsSizeForLayout))) {
@@ -314,7 +319,7 @@ ASPrimitiveTraitCollectionDeprecatedImplementation
   }
   
   as_activity_create_for_scope("Update node layout for current bounds");
-  as_log_verbose(ASLayoutLog(), "Node %@, bounds size %@, calculatedSize %@, calculatedIsDirty %d", self, NSStringFromCGSize(boundsSizeForLayout), NSStringFromCGSize(_calculatedDisplayNodeLayout->layout.size), _calculatedDisplayNodeLayout->isDirty());
+  as_log_verbose(ASLayoutLog(), "Node %@, bounds size %@, calculatedSize %@, calculatedIsDirty %d", self, NSStringFromCGSize(boundsSizeForLayout), NSStringFromCGSize(_calculatedDisplayNodeLayout->layout.size), _calculatedDisplayNodeLayout->version < _layoutVersion.load());
   // _calculatedDisplayNodeLayout is not reusable we need to transition to a new one
   [self cancelLayoutTransition];
   
@@ -352,8 +357,10 @@ ASPrimitiveTraitCollectionDeprecatedImplementation
     ASLayout *layout = [self calculateLayoutThatFits:constrainedSize
                                     restrictedToSize:self.style.size
                                 relativeToParentSize:boundsSizeForLayout];
-    
     nextLayout = std::make_shared<ASDisplayNodeLayout>(layout, constrainedSize, boundsSizeForLayout, version);
+    // Now that the constrained size of pending layout might have been reused, the layout is useless
+    // Release it and any orphaned subnodes it retains
+    _pendingDisplayNodeLayout = nullptr;
   }
   
   if (didCreateNewContext) {
@@ -373,6 +380,9 @@ ASPrimitiveTraitCollectionDeprecatedImplementation
     // particular ASLayout object, and shouldn't loop asking again unless we have a different ASLayout.
     nextLayout->requestedLayoutFromAbove = YES;
     [self _setNeedsLayoutFromAbove];
+    // Update the layout's version here because _setNeedsLayoutFromAbove calls __setNeedsLayout which in turn increases _layoutVersion
+    // Failing to do this will cause the layout to be invalid immediately 
+    nextLayout->version = _layoutVersion;
   }
 
   // Prepare to transition to nextLayout
@@ -473,6 +483,11 @@ ASPrimitiveTraitCollectionDeprecatedImplementation
 - (BOOL)_isLayoutTransitionInvalid
 {
   ASDN::MutexLocker l(__instanceLock__);
+  return [self _locked_isLayoutTransitionValid];
+}
+
+- (BOOL)_locked_isLayoutTransitionValid
+{
   if (ASHierarchyStateIncludesLayoutPending(_hierarchyState)) {
     ASLayoutElementContext *context = ASLayoutElementGetCurrentContext();
     if (context == nil || _pendingTransitionID != context.transitionID) {
@@ -505,9 +520,6 @@ ASPrimitiveTraitCollectionDeprecatedImplementation
                 measurementCompletion:(void(^)())completion
 {
   ASDisplayNodeAssertMainThread();
-
-  [self setNeedsLayout];
-  
   [self transitionLayoutWithSizeRange:[self _locked_constrainedSizeForLayoutPass]
                              animated:animated
                    shouldMeasureAsync:shouldMeasureAsync
@@ -531,16 +543,27 @@ ASPrimitiveTraitCollectionDeprecatedImplementation
     return;
   }
     
+  {
+    ASDN::MutexLocker l(__instanceLock__);
+
     // Check if we are a subnode in a layout transition.
     // In this case no measurement is needed as we're part of the layout transition.
-  if ([self _isLayoutTransitionInvalid]) {
+    if ([self _locked_isLayoutTransitionValid]) {
       return;
     }
 
-  {
+    if (ASHierarchyStateIncludesLayoutPending(_hierarchyState)) {
-    ASDN::MutexLocker l(__instanceLock__);
+      ASDisplayNodeAssert(NO, @"Can't start a transition when one of the supernodes is performing one.");
-    ASDisplayNodeAssert(ASHierarchyStateIncludesLayoutPending(_hierarchyState) == NO, @"Can't start a transition when one of the supernodes is performing one.");
+      return;
     }
+  }
+
+  // Invalidate calculated layout because this method acts as an animated "setNeedsLayout" for nodes.
+  // If the user has reconfigured the node and calls this, we should never return a stale layout
+  // for subsequent calls to layoutThatFits: regardless of size range. We choose this method rather than
+  // -setNeedsLayout because that method also triggers a CA layout invalidation, which isn't necessary at this time.
+  // See https://github.com/TextureGroup/Texture/issues/463
+  [self invalidateCalculatedLayout];
 
   // Every new layout transition has a transition id associated to check in subsequent transitions for cancelling
   int32_t transitionID = [self _startNewTransition];

Source/ASDisplayNode+Subclasses.h

@@ -96,6 +96,13 @@ NS_ASSUME_NONNULL_BEGIN
  */
 - (void)didExitPreloadState;
 
+/**
+ * @abstract Called when the node has completed applying the layout.
+ * @discussion Can be used for operations that are performed after layout has completed.
+ * @note This method is guaranteed to be called on main.
+ */
+- (void)nodeDidLayout;
+
 @end
 
 @interface ASDisplayNode (Subclassing) <ASInterfaceStateDelegate>

Source/ASDisplayNode.h

@@ -589,6 +589,11 @@ extern NSInteger const ASDefaultDrawingPriority;
  */
 - (NSString *)displayNodeRecursiveDescription AS_WARN_UNUSED_RESULT;
 
+/**
+ * A detailed description of this node's layout state. This is useful when debugging.
+ */
+@property (atomic, copy, readonly) NSString *detailedLayoutDescription;
+
 @end
 
 /**

Source/ASDisplayNode.mm

@@ -919,6 +919,8 @@ static ASDisplayNodeMethodOverrides GetASDisplayNodeMethodOverrides(Class c)
       return;
     }
 
+    as_activity_create_for_scope("-[ASDisplayNode __layout]");
+
     // This method will confirm that the layout is up to date (and update if needed).
     // Importantly, it will also APPLY the layout to all of our subnodes if (unless parent is transitioning).
     [self _locked_measureNodeWithBoundsIfNecessary:bounds];
@@ -1124,6 +1126,7 @@ static ASDisplayNodeMethodOverrides GetASDisplayNodeMethodOverrides(Class c)
   ASDisplayNodeAssertMainThread();
   ASDisplayNodeAssertLockUnownedByCurrentThread(__instanceLock__);
   ASDisplayNodeAssertTrue(self.isNodeLoaded);
+  [_interfaceStateDelegate nodeDidLayout];
 }
 
 #pragma mark Layout Transition
@@ -3380,6 +3383,38 @@ ASDISPLAYNODE_INLINE BOOL subtreeIsRasterized(ASDisplayNode *node) {
   return subtree;
 }
 
+- (NSString *)detailedLayoutDescription
+{
+  ASPushMainThreadAssertionsDisabled();
+  ASDN::MutexLocker l(__instanceLock__);
+  auto props = [NSMutableArray<NSDictionary *> array];
+
+  [props addObject:@{ @"layoutVersion": @(_layoutVersion.load()) }];
+  [props addObject:@{ @"bounds": [NSValue valueWithCGRect:self.bounds] }];
+
+  if (_calculatedDisplayNodeLayout != nullptr) {
+    ASDisplayNodeLayout c = *_calculatedDisplayNodeLayout;
+    [props addObject:@{ @"calculatedLayout": c.layout }];
+    [props addObject:@{ @"calculatedVersion": @(c.version) }];
+    [props addObject:@{ @"calculatedConstrainedSize" : NSStringFromASSizeRange(c.constrainedSize) }];
+    if (c.requestedLayoutFromAbove) {
+      [props addObject:@{ @"calculatedRequestedLayoutFromAbove": @"YES" }];
+    }
+  }
+  if (_pendingDisplayNodeLayout != nullptr) {
+    ASDisplayNodeLayout p = *_pendingDisplayNodeLayout;
+    [props addObject:@{ @"pendingLayout": p.layout }];
+    [props addObject:@{ @"pendingVersion": @(p.version) }];
+    [props addObject:@{ @"pendingConstrainedSize" : NSStringFromASSizeRange(p.constrainedSize) }];
+    if (p.requestedLayoutFromAbove) {
+      [props addObject:@{ @"pendingRequestedLayoutFromAbove": (id)kCFNull }];
+    }
+  }
+
+  ASPopMainThreadAssertionsDisabled();
+  return ASObjectDescriptionMake(self, props);
+}
+
 @end
 
 #pragma mark - ASDisplayNode UIKit / CA Categories

Source/ASNetworkImageNode.mm

@@ -672,7 +672,7 @@ static const CGSize kMinReleaseImageOnBackgroundSize = {20.0, 20.0};
           return;
         }
 
-        as_log_verbose(ASImageLoadingLog(), "Downloaded image for %@ img: %@ url: %@", self, [imageContainer asdk_image], url);
+        as_log_verbose(ASImageLoadingLog(), "Downloaded image for %@ img: %@ url: %@", self, [imageContainer asdk_image], URL);
         
         // Grab the lock for the rest of the block
         ASDN::MutexLocker l(strongSelf->__instanceLock__);

Source/ASNodeController+Beta.h

@@ -18,18 +18,15 @@
 #import <AsyncDisplayKit/ASDisplayNode.h>
 #import <AsyncDisplayKit/ASDisplayNode+Subclasses.h> // for ASInterfaceState protocol
 
-// Until an ASNodeController can be provided in place of an ASCellNode, some apps may prefer to have
-// nodes keep their controllers alive (and a weak reference from controller to node)
-#define INVERT_NODE_CONTROLLER_OWNERSHIP 0
-
 /* ASNodeController is currently beta and open to change in the future */
 @interface ASNodeController<__covariant DisplayNodeType : ASDisplayNode *> : NSObject <ASInterfaceStateDelegate>
 
-#if INVERT_NODE_CONTROLLER_OWNERSHIP
+@property (nonatomic, strong /* may be weak! */) DisplayNodeType node;
-@property (nonatomic, weak) DisplayNodeType node;
+
-#else
+// Until an ASNodeController can be provided in place of an ASCellNode, some apps may prefer to have
-@property (nonatomic, strong) DisplayNodeType node;
+// nodes keep their controllers alive (and a weak reference from controller to node)
-#endif
+
+@property (nonatomic, assign) BOOL shouldInvertStrongReference;
 
 - (void)loadNode;
 
@@ -47,3 +44,9 @@
                       fromState:(ASInterfaceState)oldState ASDISPLAYNODE_REQUIRES_SUPER;
 
 @end
+
+@interface ASDisplayNode (ASNodeController)
+
+@property(nonatomic, readonly) ASNodeController *nodeController;
+
+@end

Source/ASNodeController+Beta.m

@@ -15,34 +15,28 @@
 //      http://www.apache.org/licenses/LICENSE-2.0
 //
 
-#import "ASNodeController+Beta.h"
+#import <AsyncDisplayKit/ASWeakProxy.h>
-#import "ASDisplayNode+FrameworkPrivate.h"
+#import <AsyncDisplayKit/ASNodeController+Beta.h>
+#import <AsyncDisplayKit/ASDisplayNode+FrameworkPrivate.h>
 
-#if INVERT_NODE_CONTROLLER_OWNERSHIP
+#define _node (_shouldInvertStrongReference ? _weakNode : _strongNode)
 
-@interface ASDisplayNode (ASNodeController)
+@interface ASDisplayNode (ASNodeControllerOwnership)
-@property (nonatomic, strong) ASNodeController *asdkNodeController;
-@end
 
-@implementation ASDisplayNode (ASNodeController)
+// This property exists for debugging purposes. Don't use __nodeController in production code.
+@property (nonatomic, readonly) ASNodeController *__nodeController;
 
-- (ASNodeController *)asdkNodeController
+// These setters are mutually exclusive. Setting one will clear the relationship of the other.
-{
+- (void)__setNodeControllerStrong:(ASNodeController *)nodeController;
-  return objc_getAssociatedObject(self, @selector(asdkNodeController));
+- (void)__setNodeControllerWeak:(ASNodeController *)nodeController;
-}
-
-- (void)setAsdkNodeController:(ASNodeController *)asdkNodeController
-{
-  objc_setAssociatedObject(self, @selector(asdkNodeController), asdkNodeController, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
-}
 
 @end
 
-#endif
-
 @implementation ASNodeController
-
+{
-@synthesize node = _node;
+  ASDisplayNode *_strongNode;
+  __weak ASDisplayNode *_weakNode;
+}
 
 - (instancetype)init
 {
@@ -66,16 +60,41 @@
   return _node;
 }
 
+- (void)setupReferencesWithNode:(ASDisplayNode *)node
+{
+  if (_shouldInvertStrongReference) {
+    // The node should own the controller; weak reference from controller to node.
+    _weakNode = node;
+    [node __setNodeControllerStrong:self];
+    _strongNode = nil;
+  } else {
+    // The controller should own the node; weak reference from node to controller.
+    _strongNode = node;
+    [node __setNodeControllerWeak:self];
+    _weakNode = nil;
+  }
+
+  node.interfaceStateDelegate = self;
+}
+
 - (void)setNode:(ASDisplayNode *)node
 {
-  _node = node;
+  [self setupReferencesWithNode:node];
-  _node.interfaceStateDelegate = self;
+}
-#if INVERT_NODE_CONTROLLER_OWNERSHIP
+
-  _node.asdkNodeController = self;
+- (void)setShouldInvertStrongReference:(BOOL)shouldInvertStrongReference
-#endif
+{
+  if (_shouldInvertStrongReference != shouldInvertStrongReference) {
+    // Because the BOOL controls which ivar we access, get the node before toggling.
+    ASDisplayNode *node = _node;
+    _shouldInvertStrongReference = shouldInvertStrongReference;
+    [self setupReferencesWithNode:node];
+  }
 }
 
 // subclass overrides
+- (void)nodeDidLayout {}
+
 - (void)didEnterVisibleState {}
 - (void)didExitVisibleState  {}
 
@@ -89,3 +108,41 @@
                       fromState:(ASInterfaceState)oldState {}
 
 @end
+
+@implementation ASDisplayNode (ASNodeControllerOwnership)
+
+- (ASNodeController *)__nodeController
+{
+  ASNodeController *nodeController = nil;
+  id object = objc_getAssociatedObject(self, @selector(__nodeController));
+
+  if ([object isKindOfClass:[ASWeakProxy class]]) {
+    nodeController = (ASNodeController *)[(ASWeakProxy *)object target];
+  } else {
+    nodeController = (ASNodeController *)object;
+  }
+
+  return nodeController;
+}
+
+- (void)__setNodeControllerStrong:(ASNodeController *)nodeController
+{
+  objc_setAssociatedObject(self, @selector(__nodeController), nodeController, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
+}
+
+- (void)__setNodeControllerWeak:(ASNodeController *)nodeController
+{
+  // Associated objects don't support weak references. Since assign can become a dangling pointer, use ASWeakProxy.
+  ASWeakProxy *nodeControllerProxy = [ASWeakProxy weakProxyWithTarget:nodeController];
+  objc_setAssociatedObject(self, @selector(__nodeController), nodeControllerProxy, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
+}
+
+@end
+
+@implementation ASDisplayNode (ASNodeController)
+
+- (ASNodeController *)nodeController {
+  return self.__nodeController;
+}
+
+@end

Source/ASPagerNode+Beta.h

@@ -0,0 +1,19 @@
+//
+//  ASPagerNode+Beta.h
+//  Texture
+//
+//  Copyright (c) 2017-present, Pinterest, Inc.  All rights reserved.
+//  Licensed under the Apache License, Version 2.0 (the "License");
+//  you may not use this file except in compliance with the License.
+//  You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+
+#import <AsyncDisplayKit/ASPagerNode.h>
+
+@interface ASPagerNode (Beta)
+
+- (instancetype)initUsingAsyncCollectionLayout;
+
+@end

Source/ASPagerNode.m

@@ -17,6 +17,10 @@
 
 #ifndef MINIMAL_ASDK
 #import <AsyncDisplayKit/ASPagerNode.h>
+#import <AsyncDisplayKit/ASPagerNode+Beta.h>
+
+#import <AsyncDisplayKit/ASCollectionGalleryLayoutDelegate.h>
+#import <AsyncDisplayKit/ASCollectionNode+Beta.h>
 #import <AsyncDisplayKit/ASDelegateProxy.h>
 #import <AsyncDisplayKit/ASDisplayNode+FrameworkPrivate.h>
 #import <AsyncDisplayKit/ASDisplayNode+Subclasses.h>
@@ -26,10 +30,8 @@
 #import <AsyncDisplayKit/ASCollectionView+Undeprecated.h>
 #import <AsyncDisplayKit/UIResponder+AsyncDisplayKit.h>
 
-@interface ASPagerNode () <ASCollectionDataSource, ASCollectionDelegate, ASCollectionDelegateFlowLayout, ASDelegateProxyInterceptor>
+@interface ASPagerNode () <ASCollectionDataSource, ASCollectionDelegate, ASCollectionDelegateFlowLayout, ASDelegateProxyInterceptor, ASCollectionGalleryLayoutSizeProviding>
 {
-  ASPagerFlowLayout *_flowLayout;
-
   __weak id <ASPagerDataSource> _pagerDataSource;
   ASPagerNodeProxy *_proxyDataSource;
   struct {
@@ -66,8 +68,15 @@
 {
   ASDisplayNodeAssert([flowLayout isKindOfClass:[ASPagerFlowLayout class]], @"ASPagerNode requires a flow layout.");
   self = [super initWithCollectionViewLayout:flowLayout];
-  if (self != nil) {
+  return self;
-    _flowLayout = flowLayout;
+}
+
+- (instancetype)initUsingAsyncCollectionLayout
+{
+  ASCollectionGalleryLayoutDelegate *layoutDelegate = [[ASCollectionGalleryLayoutDelegate alloc] initWithScrollableDirections:ASScrollDirectionHorizontalDirections];
+  self = [super initWithLayoutDelegate:layoutDelegate layoutFacilitator:nil];
+  if (self) {
+    layoutDelegate.sizeProvider = self;
   }
   return self;
 }
@@ -129,6 +138,14 @@
   return indexPath.row;
 }
 
+#pragma mark - ASCollectionGalleryLayoutSizeProviding
+
+- (CGSize)sizeForElements:(ASElementMap *)elements
+{
+  ASDisplayNodeAssertMainThread();
+  return self.bounds.size;
+}
+
 #pragma mark - ASCollectionDataSource
 
 - (ASCellNodeBlock)collectionNode:(ASCollectionNode *)collectionNode nodeBlockForItemAtIndexPath:(NSIndexPath *)indexPath

Source/ASTableView.mm

@@ -1475,19 +1475,7 @@ static NSString * const kCellReuseIdentifier = @"_ASTableViewCell";
 
 #pragma mark - ASRangeControllerDelegate
 
-- (void)rangeController:(ASRangeController *)rangeController willUpdateWithChangeSet:(_ASHierarchyChangeSet *)changeSet
+- (void)rangeController:(ASRangeController *)rangeController updateWithChangeSet:(_ASHierarchyChangeSet *)changeSet updates:(dispatch_block_t)updates
-{
-  ASDisplayNodeAssertMainThread();
-  if (!self.asyncDataSource) {
-    return; // if the asyncDataSource has become invalid while we are processing, ignore this request to avoid crashes
-  }
-  
-  if (_automaticallyAdjustsContentOffset && !changeSet.includesReloadData) {
-    [self beginAdjustingContentOffset];
-  }
-}
-
-- (void)rangeController:(ASRangeController *)rangeController didUpdateWithChangeSet:(_ASHierarchyChangeSet *)changeSet updates:(dispatch_block_t)updates
 {
   ASDisplayNodeAssertMainThread();
   if (!self.asyncDataSource || _updatingInResponseToInteractiveMove) {
@@ -1512,6 +1500,11 @@ static NSString * const kCellReuseIdentifier = @"_ASTableViewCell";
     return;
   }
 
+  BOOL shouldAdjustContentOffset = (_automaticallyAdjustsContentOffset && !changeSet.includesReloadData);
+  if (shouldAdjustContentOffset) {
+    [self beginAdjustingContentOffset];
+  }
+  
   NSUInteger numberOfUpdates = 0;
   
   LOG(@"--- UITableView beginUpdates");
@@ -1621,7 +1614,7 @@ static NSString * const kCellReuseIdentifier = @"_ASTableViewCell";
     [_rangeController updateIfNeeded];
     [self _scheduleCheckForBatchFetchingForNumberOfChanges:numberOfUpdates];
   });
-  if (_automaticallyAdjustsContentOffset) {
+  if (shouldAdjustContentOffset) {
     [self endAdjustingContentOffsetAnimated:changeSet.animated];
   }
   [changeSet executeCompletionHandlerWithFinished:YES];

Source/AsyncDisplayKit.h

@@ -42,6 +42,7 @@
 #import <AsyncDisplayKit/ASTableNode.h>
 #import <AsyncDisplayKit/ASCollectionView.h>
 #import <AsyncDisplayKit/ASCollectionNode.h>
+#import <AsyncDisplayKit/ASCollectionNode+Beta.h>
 #import <AsyncDisplayKit/ASCollectionViewLayoutInspector.h>
 #import <AsyncDisplayKit/ASCollectionViewLayoutFacilitatorProtocol.h>
 #import <AsyncDisplayKit/ASCellNode.h>
@@ -61,6 +62,7 @@
 
 #import <AsyncDisplayKit/ASPagerFlowLayout.h>
 #import <AsyncDisplayKit/ASPagerNode.h>
+#import <AsyncDisplayKit/ASPagerNode+Beta.h>
 
 #import <AsyncDisplayKit/ASNodeController+Beta.h>
 #import <AsyncDisplayKit/ASViewController.h>
@@ -125,7 +127,5 @@
 #import <AsyncDisplayKit/AsyncDisplayKit+Tips.h>
 #import <AsyncDisplayKit/ASDisplayNode+Deprecated.h>
 
-#import <AsyncDisplayKit/ASCollectionNode+Beta.h>
-
 #import <AsyncDisplayKit/IGListAdapter+AsyncDisplayKit.h>
 #import <AsyncDisplayKit/AsyncDisplayKit+IGListKitMethods.h>

Source/Details/ASCollectionElement.h

@@ -28,7 +28,6 @@ NS_ASSUME_NONNULL_BEGIN
 AS_SUBCLASSING_RESTRICTED
 @interface ASCollectionElement : NSObject
 
-//TODO change this to be a generic "kind" or "elementKind" that exposes `nil` for row kind
 @property (nonatomic, readonly, copy, nullable) NSString *supplementaryElementKind;
 @property (nonatomic, assign) ASSizeRange constrainedSize;
 @property (nonatomic, readonly, weak) id<ASRangeManagingNode> owningNode;

Source/Details/ASCollectionFlowLayoutDelegate.m

@@ -48,11 +48,13 @@
 
 - (ASScrollDirection)scrollableDirections
 {
+  ASDisplayNodeAssertMainThread();
   return _scrollableDirections;
 }
 
 - (id)additionalInfoForLayoutWithElements:(ASElementMap *)elements
 {
+  ASDisplayNodeAssertMainThread();
   return nil;
 }
 
@@ -61,9 +63,7 @@
   ASElementMap *elements = context.elements;
   NSMutableArray<ASCellNode *> *children = ASArrayByFlatMapping(elements.itemElements, ASCollectionElement *element, element.node);
   if (children.count == 0) {
-    return [[ASCollectionLayoutState alloc] initWithContext:context
+    return [[ASCollectionLayoutState alloc] initWithContext:context];
-                                                contentSize:CGSizeZero
-                             elementToLayoutAttributesTable:[NSMapTable elementToLayoutAttributesTable]];
   }
   
   ASStackLayoutSpec *stackSpec = [ASStackLayoutSpec stackLayoutSpecWithDirection:ASStackLayoutDirectionHorizontal

Source/Details/ASCollectionGalleryLayoutDelegate.h

@@ -15,8 +15,25 @@
 #import <AsyncDisplayKit/ASCollectionLayoutDelegate.h>
 #import <AsyncDisplayKit/ASScrollDirection.h>
 
+@class ASElementMap;
+
 NS_ASSUME_NONNULL_BEGIN
 
+@protocol ASCollectionGalleryLayoutSizeProviding <NSObject>
+
+/**
+ * Returns the fixed size of each and every element.
+ *
+ * @discussion This method will only be called on main thread.
+ *
+ * @param elements All elements to be sized.
+ *
+ * @return The elements' size
+ */
+- (CGSize)sizeForElements:(ASElementMap *)elements;
+
+@end
+
 /**
  * A thread-safe layout delegate that arranges items with the same size into a flow layout.
  *
@@ -25,7 +42,9 @@ NS_ASSUME_NONNULL_BEGIN
 AS_SUBCLASSING_RESTRICTED
 @interface ASCollectionGalleryLayoutDelegate : NSObject <ASCollectionLayoutDelegate>
 
-- (instancetype)initWithScrollableDirections:(ASScrollDirection)scrollableDirections itemSize:(CGSize)itemSize NS_DESIGNATED_INITIALIZER;
+@property (nonatomic, weak) id<ASCollectionGalleryLayoutSizeProviding> sizeProvider;
+
+- (instancetype)initWithScrollableDirections:(ASScrollDirection)scrollableDirections NS_DESIGNATED_INITIALIZER;
 
 - (instancetype)init __unavailable;
 

Source/Details/ASCollectionGalleryLayoutDelegate.m

@@ -33,40 +33,47 @@
   CGSize _itemSize;
 }
 
-- (instancetype)initWithScrollableDirections:(ASScrollDirection)scrollableDirections itemSize:(CGSize)itemSize
+- (instancetype)initWithScrollableDirections:(ASScrollDirection)scrollableDirections
 {
   self = [super init];
   if (self) {
-    ASDisplayNodeAssertFalse(CGSizeEqualToSize(CGSizeZero, itemSize));
     _scrollableDirections = scrollableDirections;
-    _itemSize = itemSize;
   }
   return self;
 }
 
 - (ASScrollDirection)scrollableDirections
 {
+  ASDisplayNodeAssertMainThread();
   return _scrollableDirections;
 }
 
 - (id)additionalInfoForLayoutWithElements:(ASElementMap *)elements
 {
-  return [NSValue valueWithCGSize:_itemSize];
+  ASDisplayNodeAssertMainThread();
+  if (_sizeProvider == nil) {
+    return nil;
+  }
+
+  return [NSValue valueWithCGSize:[_sizeProvider sizeForElements:elements]];
 }
 
 + (ASCollectionLayoutState *)calculateLayoutWithContext:(ASCollectionLayoutContext *)context
 {
   ASElementMap *elements = context.elements;
   CGSize pageSize = context.viewportSize;
-  CGSize itemSize = ((NSValue *)context.additionalInfo).CGSizeValue;
   ASScrollDirection scrollableDirections = context.scrollableDirections;
+
+  CGSize itemSize = context.additionalInfo ? ((NSValue *)context.additionalInfo).CGSizeValue : CGSizeZero;
+  if (CGSizeEqualToSize(CGSizeZero, itemSize)) {
+    return [[ASCollectionLayoutState alloc] initWithContext:context];
+  }
+
   NSMutableArray<_ASGalleryLayoutItem *> *children = ASArrayByFlatMapping(elements.itemElements,
                                                                           ASCollectionElement *element,
                                                                           [[_ASGalleryLayoutItem alloc] initWithItemSize:itemSize collectionElement:element]);
   if (children.count == 0) {
-    return [[ASCollectionLayoutState alloc] initWithContext:context
+    return [[ASCollectionLayoutState alloc] initWithContext:context];
-                                                contentSize:CGSizeZero
-                             elementToLayoutAttributesTable:[NSMapTable weakToStrongObjectsMapTable]];
   }
   
   // Use a stack spec to calculate layout content size and frames of all elements without actually measuring each element

Source/Details/ASCollectionLayoutContext.m

@@ -39,7 +39,6 @@
 {
   self = [super init];
   if (self) {
-    ASDisplayNodeAssertTrue([layoutDelegateClass conformsToProtocol:@protocol(ASCollectionLayoutDelegate)]);
     _viewportSize = viewportSize;
     _scrollableDirections = scrollableDirections;
     _elements = elements;

Source/Details/ASCollectionLayoutDelegate.h

@@ -32,6 +32,8 @@ NS_ASSUME_NONNULL_BEGIN
  * It will be available in the context parameter in +calculateLayoutWithContext:
  *
  * @return The scrollable directions.
+ *
+ * @discusstion This method will be called on main thread.
  */
 - (ASScrollDirection)scrollableDirections;
 

Source/Details/ASCollectionLayoutState.h

@@ -58,6 +58,13 @@ AS_SUBCLASSING_RESTRICTED
                     contentSize:(CGSize)contentSize
  elementToLayoutAttributesTable:(NSMapTable<ASCollectionElement *, UICollectionViewLayoutAttributes *> *)table NS_DESIGNATED_INITIALIZER;
 
+/**
+ * Convenience initializer. Returns an object with zero content size and an empty table.
+ *
+ * @param context The context used to calculate this object
+ */
+- (instancetype)initWithContext:(ASCollectionLayoutContext *)context;
+
 /**
  * Convenience initializer.
  *

Source/Details/ASCollectionLayoutState.mm

@@ -41,6 +41,13 @@
   ASPageToLayoutAttributesTable *_unmeasuredPageToLayoutAttributesTable;
 }
 
+- (instancetype)initWithContext:(ASCollectionLayoutContext *)context
+{
+  return [self initWithContext:context
+                   contentSize:CGSizeZero
+elementToLayoutAttributesTable:[NSMapTable elementToLayoutAttributesTable]];
+}
+
 - (instancetype)initWithContext:(ASCollectionLayoutContext *)context
                          layout:(ASLayout *)layout
                 getElementBlock:(ASCollectionElement *(^)(ASLayout *))getElementBlock

Source/Details/ASDataController.h

@@ -109,13 +109,6 @@ extern NSString * const ASCollectionInvalidUpdateException;
  */
 @protocol ASDataControllerDelegate <NSObject>
 
-/**
- * Called before updating with given change set.
- *
- * @param changeSet The change set that includes all updates
- */
-- (void)dataController:(ASDataController *)dataController willUpdateWithChangeSet:(_ASHierarchyChangeSet *)changeSet;
-
 /**
  * Called for change set updates.
  *
@@ -127,7 +120,7 @@ extern NSString * const ASCollectionInvalidUpdateException;
  * It should be called at the time the backing view is ready to process the updates,
  * i.e inside the updates block of `-[UICollectionView performBatchUpdates:completion:] or after calling `-[UITableView beginUpdates]`.
  */
-- (void)dataController:(ASDataController *)dataController didUpdateWithChangeSet:(_ASHierarchyChangeSet *)changeSet updates:(dispatch_block_t)updates;
+- (void)dataController:(ASDataController *)dataController updateWithChangeSet:(_ASHierarchyChangeSet *)changeSet updates:(dispatch_block_t)updates;
 
 @end
 

Source/Details/ASDataController.mm

@@ -46,10 +46,8 @@
 //#define LOG(...) NSLog(__VA_ARGS__)
 #define LOG(...)
 
-#define RETURN_IF_NO_DATASOURCE(val) if (_dataSource == nil) { return val; }
 #define ASSERT_ON_EDITING_QUEUE ASDisplayNodeAssertNotNil(dispatch_get_specific(&kASDataControllerEditingQueueKey), @"%@ must be called on the editing transaction queue.", NSStringFromSelector(_cmd))
 
-const static NSUInteger kASDataControllerSizingCountPerProcessor = 5;
 const static char * kASDataControllerEditingQueueKey = "kASDataControllerEditingQueueKey";
 const static char * kASDataControllerEditingQueueContext = "kASDataControllerEditingQueueContext";
 
@@ -125,18 +123,6 @@ typedef dispatch_block_t ASDataControllerCompletionBlock;
   return self;
 }
 
-+ (NSUInteger)parallelProcessorCount
-{
-  static NSUInteger parallelProcessorCount;
-
-  static dispatch_once_t onceToken;
-  dispatch_once(&onceToken, ^{
-    parallelProcessorCount = [[NSProcessInfo processInfo] activeProcessorCount];
-  });
-
-  return parallelProcessorCount;
-}
-
 - (id<ASDataControllerLayoutDelegate>)layoutDelegate
 {
   ASDisplayNodeAssertMainThread();
@@ -153,34 +139,47 @@ typedef dispatch_block_t ASDataControllerCompletionBlock;
 
 #pragma mark - Cell Layout
 
-- (void)batchAllocateNodesFromElements:(NSArray<ASCollectionElement *> *)elements batchSize:(NSInteger)batchSize batchCompletion:(ASDataControllerCompletionBlock)batchCompletionHandler
+- (void)_allocateNodesFromElements:(NSArray<ASCollectionElement *> *)elements completion:(ASDataControllerCompletionBlock)completionHandler
 {
   ASSERT_ON_EDITING_QUEUE;
   
-  if (elements.count == 0 || _dataSource == nil) {
+  NSUInteger nodeCount = elements.count;
-    batchCompletionHandler();
+  __weak id<ASDataControllerSource> weakDataSource = _dataSource;
+  if (nodeCount == 0 || weakDataSource == nil) {
+    completionHandler();
     return;
   }
 
   ASSignpostStart(ASSignpostDataControllerBatch);
 
-  if (batchSize == 0) {
-    batchSize = [[ASDataController class] parallelProcessorCount] * kASDataControllerSizingCountPerProcessor;
-  }
-  NSUInteger count = elements.count;
-  
-  // Processing in batches
-  for (NSUInteger i = 0; i < count; i += batchSize) {
-    NSRange batchedRange = NSMakeRange(i, MIN(count - i, batchSize));
-    NSArray<ASCollectionElement *> *batchedElements = [elements subarrayWithRange:batchedRange];
   {
     as_activity_create_for_scope("Data controller batch");
-      [self _allocateNodesFromElements:batchedElements];
+
-    }
+    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
-    batchCompletionHandler();
+    ASDispatchApply(nodeCount, queue, 0, ^(size_t i) {
+      __strong id<ASDataControllerSource> strongDataSource = weakDataSource;
+      if (strongDataSource == nil) {
+        return;
       }
 
-  ASSignpostEndCustom(ASSignpostDataControllerBatch, self, 0, (_dataSource != nil ? ASSignpostColorDefault : ASSignpostColorRed));
+      // Allocate the node.
+      ASCollectionElement *context = elements[i];
+      ASCellNode *node = context.node;
+      if (node == nil) {
+        ASDisplayNodeAssertNotNil(node, @"Node block created nil node; %@, %@", self, strongDataSource);
+        node = [[ASCellNode alloc] init]; // Fallback to avoid crash for production apps.
+      }
+
+      // Layout the node if the size range is valid.
+      ASSizeRange sizeRange = context.constrainedSize;
+      if (ASSizeRangeHasSignificantArea(sizeRange)) {
+        [self _layoutNode:node withConstrainedSize:sizeRange];
+      }
+    });
+  }
+
+  completionHandler();
+  ASSignpostEndCustom(ASSignpostDataControllerBatch, self, 0, (weakDataSource != nil ? ASSignpostColorDefault : ASSignpostColorRed));
 }
 
 /**
@@ -195,36 +194,6 @@ typedef dispatch_block_t ASDataControllerCompletionBlock;
   node.frame = frame;
 }
 
-// TODO Is returned array still needed? Can it be removed?
-- (void)_allocateNodesFromElements:(NSArray<ASCollectionElement *> *)elements
-{
-  ASSERT_ON_EDITING_QUEUE;
-  
-  NSUInteger nodeCount = elements.count;
-  if (!nodeCount || _dataSource == nil) {
-    return;
-  }
-
-  dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
-  ASDispatchApply(nodeCount, queue, 0, ^(size_t i) {
-    RETURN_IF_NO_DATASOURCE();
-
-    // Allocate the node.
-    ASCollectionElement *context = elements[i];
-    ASCellNode *node = context.node;
-    if (node == nil) {
-      ASDisplayNodeAssertNotNil(node, @"Node block created nil node; %@, %@", self, self.dataSource);
-      node = [[ASCellNode alloc] init]; // Fallback to avoid crash for production apps.
-    }
-    
-    // Layout the node if the size range is valid.
-    ASSizeRange sizeRange = context.constrainedSize;
-    if (ASSizeRangeHasSignificantArea(sizeRange)) {
-      [self _layoutNode:node withConstrainedSize:sizeRange];
-    }
-  });
-}
-
 #pragma mark - Data Source Access (Calling _dataSource)
 
 - (NSArray<NSIndexPath *> *)_allIndexPathsForItemsOfKind:(NSString *)kind inSections:(NSIndexSet *)sections
@@ -435,21 +404,16 @@ typedef dispatch_block_t ASDataControllerCompletionBlock;
   return @[];
 }
 
-- (ASSizeRange)constrainedSizeForElement:(ASCollectionElement *)element inElementMap:(ASElementMap *)map
+/**
-{
+ * Returns constrained size for the node of the given kind and at the given index path.
-  ASDisplayNodeAssertMainThread();
+ * NOTE: index path must be in the data-source index space.
-  NSString *kind = element.supplementaryElementKind ?: ASDataControllerRowNodeKind;
+ */
-  NSIndexPath *indexPath = [map indexPathForElement:element];
-  return [self constrainedSizeForNodeOfKind:kind atIndexPath:indexPath];
-}
-
-
 - (ASSizeRange)constrainedSizeForNodeOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath
 {
   ASDisplayNodeAssertMainThread();
   
   id<ASDataControllerSource> dataSource = _dataSource;
-  if (dataSource == nil) {
+  if (dataSource == nil || indexPath == nil) {
     return ASSizeRangeZero;
   }
   
@@ -574,11 +538,8 @@ typedef dispatch_block_t ASDataControllerCompletionBlock;
     dispatch_block_t completion = ^() {
       [_mainSerialQueue performBlockOnMainThread:^{
         as_activity_scope_leave(&preparationScope);
-        // TODO Merge the two delegate methods below
-        [_delegate dataController:self willUpdateWithChangeSet:changeSet];
-
         // Step 4: Inform the delegate
-        [_delegate dataController:self didUpdateWithChangeSet:changeSet updates:^{
+        [_delegate dataController:self updateWithChangeSet:changeSet updates:^{
           // Step 5: Deploy the new data as "completed"
           //
           // Note that since the backing collection view might be busy responding to user events (e.g scrolling),
@@ -599,7 +560,7 @@ typedef dispatch_block_t ASDataControllerCompletionBlock;
       NSArray<ASCollectionElement *> *elementsToProcess = ASArrayByFlatMapping(newMap,
                                                                                ASCollectionElement *element,
                                                                                (element.nodeIfAllocated.calculatedLayout == nil ? element : nil));
-      [self batchAllocateNodesFromElements:elementsToProcess batchSize:elementsToProcess.count batchCompletion:completion];
+      [self _allocateNodesFromElements:elementsToProcess completion:completion];
     }
   });
   
@@ -752,15 +713,18 @@ typedef dispatch_block_t ASDataControllerCompletionBlock;
   auto pendingMap = self.pendingMap;
   for (ASCellNode *node in nodes) {
     auto element = node.collectionElement;
+    NSIndexPath *indexPathInPendingMap = [pendingMap indexPathForElement:element];
     // Ensure the element is present in both maps or skip it. If it's not in the visible map,
     // then we can't check the presented size. If it's not in the pending map, we can't get the constrained size.
     // This will only happen if the element has been deleted, so the specifics of this behavior aren't important.
-    if ([visibleMap indexPathForElement:element] == nil || [pendingMap indexPathForElement:element] == nil) {
+    if (indexPathInPendingMap == nil || [visibleMap indexPathForElement:element] == nil) {
       continue;
     }
 
-    ASSizeRange constrainedSize = [self constrainedSizeForElement:element inElementMap:pendingMap];
+    NSString *kind = element.supplementaryElementKind ?: ASDataControllerRowNodeKind;
+    ASSizeRange constrainedSize = [self constrainedSizeForNodeOfKind:kind atIndexPath:indexPathInPendingMap];
     [self _layoutNode:node withConstrainedSize:constrainedSize];
+
     BOOL matchesSize = [dataSource dataController:self presentedSizeForElement:element matchesSize:node.frame.size];
     if (! matchesSize) {
       [nodesSizesChanged addObject:node];
@@ -787,15 +751,23 @@ typedef dispatch_block_t ASDataControllerCompletionBlock;
 {
   ASDisplayNodeAssertMainThread();
   for (ASCollectionElement *element in _visibleMap) {
-    ASSizeRange constrainedSize = [self constrainedSizeForElement:element inElementMap:_visibleMap];
+    // Ignore this element if it is no longer in the latest data. It is still recognized in the UIKit world but will be deleted soon.
-    if (ASSizeRangeHasSignificantArea(constrainedSize)) {
+    NSIndexPath *indexPathInPendingMap = [_pendingMap indexPathForElement:element];
-      element.constrainedSize = constrainedSize;
+    if (indexPathInPendingMap == nil) {
+      continue;
+    }
+
+    NSString *kind = element.supplementaryElementKind ?: ASDataControllerRowNodeKind;
+    ASSizeRange newConstrainedSize = [self constrainedSizeForNodeOfKind:kind atIndexPath:indexPathInPendingMap];
+
+    if (ASSizeRangeHasSignificantArea(newConstrainedSize)) {
+      element.constrainedSize = newConstrainedSize;
 
       // Node may not be allocated yet (e.g node virtualization or same size optimization)
       // Call context.nodeIfAllocated here to avoid immature node allocation and layout
       ASCellNode *node = element.nodeIfAllocated;
       if (node) {
-        [self _layoutNode:node withConstrainedSize:constrainedSize];
+        [self _layoutNode:node withConstrainedSize:newConstrainedSize];
       }
     }
   }

Source/Details/ASDelegateProxy.m

@@ -76,6 +76,9 @@
           // handled by ASCollectionView node<->cell machinery
           selector == @selector(collectionView:cellForItemAtIndexPath:) ||
           selector == @selector(collectionView:layout:sizeForItemAtIndexPath:) ||
+          selector == @selector(collectionView:layout:insetForSectionAtIndex:) ||
+          selector == @selector(collectionView:layout:minimumLineSpacingForSectionAtIndex:) ||
+          selector == @selector(collectionView:layout:minimumInteritemSpacingForSectionAtIndex:) ||
           selector == @selector(collectionView:layout:referenceSizeForHeaderInSection:) ||
           selector == @selector(collectionView:layout:referenceSizeForFooterInSection:) ||
           selector == @selector(collectionView:viewForSupplementaryElementOfKind:atIndexPath:) ||

Source/Details/ASElementMap.m

@@ -115,7 +115,7 @@
 
 - (nullable NSIndexPath *)indexPathForElement:(ASCollectionElement *)element
 {
-  return [_elementToIndexPathMap objectForKey:element];
+  return element ? [_elementToIndexPathMap objectForKey:element] : nil;
 }
 
 - (nullable NSIndexPath *)indexPathForElementIfCell:(ASCollectionElement *)element

Source/Details/ASRangeController.h

@@ -148,14 +148,7 @@ AS_SUBCLASSING_RESTRICTED
 @protocol ASRangeControllerDelegate <NSObject>
 
 /**
- * Called before updating with given change set.
+ * Called to update with given change set.
- *
- * @param changeSet The change set that includes all updates
- */
-- (void)rangeController:(ASRangeController *)rangeController willUpdateWithChangeSet:(_ASHierarchyChangeSet *)changeSet;
-
-/**
- * Called after updating with given change set.
  *
  * @param changeSet The change set that includes all updates
  *
@@ -165,7 +158,7 @@ AS_SUBCLASSING_RESTRICTED
  * It should be called at the time the backing view is ready to process the updates,
  * i.e inside the updates block of `-[UICollectionView performBatchUpdates:completion:] or after calling `-[UITableView beginUpdates]`.
  */
-- (void)rangeController:(ASRangeController *)rangeController didUpdateWithChangeSet:(_ASHierarchyChangeSet *)changeSet updates:(dispatch_block_t)updates;
+- (void)rangeController:(ASRangeController *)rangeController updateWithChangeSet:(_ASHierarchyChangeSet *)changeSet updates:(dispatch_block_t)updates;
 
 @end
 

Source/Details/ASRangeController.mm

@@ -494,20 +494,14 @@ static UIApplicationState __ApplicationState = UIApplicationStateActive;
 
 #pragma mark - ASDataControllerDelegete
 
-- (void)dataController:(ASDataController *)dataController willUpdateWithChangeSet:(_ASHierarchyChangeSet *)changeSet
+- (void)dataController:(ASDataController *)dataController updateWithChangeSet:(_ASHierarchyChangeSet *)changeSet updates:(dispatch_block_t)updates
 {
   ASDisplayNodeAssertMainThread();
   if (changeSet.includesReloadData) {
     [self _setVisibleNodes:nil];
   }
-  [_delegate rangeController:self willUpdateWithChangeSet:changeSet];
-}
-
-- (void)dataController:(ASDataController *)dataController didUpdateWithChangeSet:(_ASHierarchyChangeSet *)changeSet updates:(dispatch_block_t)updates
-{
-  ASDisplayNodeAssertMainThread();
   _rangeIsValid = NO;
-  [_delegate rangeController:self didUpdateWithChangeSet:changeSet updates:updates];
+  [_delegate rangeController:self updateWithChangeSet:changeSet updates:updates];
 }
 
 #pragma mark - Memory Management

Source/Layout/ASStackLayoutSpec.h

@@ -70,6 +70,8 @@ NS_ASSUME_NONNULL_BEGIN
 @property (nonatomic, assign) ASStackLayoutFlexWrap flexWrap;
 /** Orientation of lines along cross axis if there are multiple lines. Defaults to ASStackLayoutAlignContentStart */
 @property (nonatomic, assign) ASStackLayoutAlignContent alignContent;
+/** If the stack spreads on multiple lines using flexWrap, the amount of space between lines. */
+@property (nonatomic, assign) CGFloat lineSpacing;
 /** Whether this stack can dispatch to other threads, regardless of which thread it's running on */
 @property (nonatomic, assign, getter=isConcurrent) BOOL concurrent;
 
@@ -105,6 +107,25 @@ NS_ASSUME_NONNULL_BEGIN
                                 alignContent:(ASStackLayoutAlignContent)alignContent
                                     children:(NSArray<id<ASLayoutElement>> *)children AS_WARN_UNUSED_RESULT;
 
+/**
+ @param direction The direction of the stack view (horizontal or vertical)
+ @param spacing The spacing between the children
+ @param justifyContent If no children are flexible, this describes how to fill any extra space
+ @param alignItems Orientation of the children along the cross axis
+ @param flexWrap Whether children are stacked into a single or multiple lines
+ @param alignContent Orientation of lines along cross axis if there are multiple lines
+ @param lineSpacing The spacing between lines
+ @param children ASLayoutElement children to be positioned.
+ */
++ (instancetype)stackLayoutSpecWithDirection:(ASStackLayoutDirection)direction
+                                     spacing:(CGFloat)spacing
+                              justifyContent:(ASStackLayoutJustifyContent)justifyContent
+                                  alignItems:(ASStackLayoutAlignItems)alignItems
+                                    flexWrap:(ASStackLayoutFlexWrap)flexWrap
+                                alignContent:(ASStackLayoutAlignContent)alignContent
+                                 lineSpacing:(CGFloat)lineSpacing
+                                    children:(NSArray<id<ASLayoutElement>> *)children AS_WARN_UNUSED_RESULT;
+
 /**
  * @return A stack layout spec with direction of ASStackLayoutDirectionVertical
  **/

Source/Layout/ASStackLayoutSpec.mm

@@ -33,17 +33,22 @@
 
 - (instancetype)init
 {
-  return [self initWithDirection:ASStackLayoutDirectionHorizontal spacing:0.0 justifyContent:ASStackLayoutJustifyContentStart alignItems:ASStackLayoutAlignItemsStretch flexWrap:ASStackLayoutFlexWrapNoWrap alignContent:ASStackLayoutAlignContentStart children:nil];
+  return [self initWithDirection:ASStackLayoutDirectionHorizontal spacing:0.0 justifyContent:ASStackLayoutJustifyContentStart alignItems:ASStackLayoutAlignItemsStretch flexWrap:ASStackLayoutFlexWrapNoWrap alignContent:ASStackLayoutAlignContentStart lineSpacing:0.0 children:nil];
 }
 
 + (instancetype)stackLayoutSpecWithDirection:(ASStackLayoutDirection)direction spacing:(CGFloat)spacing justifyContent:(ASStackLayoutJustifyContent)justifyContent alignItems:(ASStackLayoutAlignItems)alignItems children:(NSArray *)children
 {
-  return [[self alloc] initWithDirection:direction spacing:spacing justifyContent:justifyContent alignItems:alignItems flexWrap:ASStackLayoutFlexWrapNoWrap alignContent:ASStackLayoutAlignContentStart children:children];
+  return [[self alloc] initWithDirection:direction spacing:spacing justifyContent:justifyContent alignItems:alignItems flexWrap:ASStackLayoutFlexWrapNoWrap alignContent:ASStackLayoutAlignContentStart lineSpacing: 0.0 children:children];
 }
 
 + (instancetype)stackLayoutSpecWithDirection:(ASStackLayoutDirection)direction spacing:(CGFloat)spacing justifyContent:(ASStackLayoutJustifyContent)justifyContent alignItems:(ASStackLayoutAlignItems)alignItems flexWrap:(ASStackLayoutFlexWrap)flexWrap alignContent:(ASStackLayoutAlignContent)alignContent children:(NSArray<id<ASLayoutElement>> *)children
 {
-  return [[self alloc] initWithDirection:direction spacing:spacing justifyContent:justifyContent alignItems:alignItems flexWrap:flexWrap alignContent:alignContent children:children];
+  return [[self alloc] initWithDirection:direction spacing:spacing justifyContent:justifyContent alignItems:alignItems flexWrap:flexWrap alignContent:alignContent lineSpacing:0.0 children:children];
+}
+
++ (instancetype)stackLayoutSpecWithDirection:(ASStackLayoutDirection)direction spacing:(CGFloat)spacing justifyContent:(ASStackLayoutJustifyContent)justifyContent alignItems:(ASStackLayoutAlignItems)alignItems flexWrap:(ASStackLayoutFlexWrap)flexWrap alignContent:(ASStackLayoutAlignContent)alignContent lineSpacing:(CGFloat)lineSpacing children:(NSArray<id<ASLayoutElement>> *)children
+{
+  return [[self alloc] initWithDirection:direction spacing:spacing justifyContent:justifyContent alignItems:alignItems flexWrap:flexWrap alignContent:alignContent lineSpacing:lineSpacing children:children];
 }
 
 + (instancetype)verticalStackLayoutSpec
@@ -60,7 +65,7 @@
   return stackLayoutSpec;
 }
 
-- (instancetype)initWithDirection:(ASStackLayoutDirection)direction spacing:(CGFloat)spacing justifyContent:(ASStackLayoutJustifyContent)justifyContent alignItems:(ASStackLayoutAlignItems)alignItems flexWrap:(ASStackLayoutFlexWrap)flexWrap alignContent:(ASStackLayoutAlignContent)alignContent children:(NSArray *)children
+- (instancetype)initWithDirection:(ASStackLayoutDirection)direction spacing:(CGFloat)spacing justifyContent:(ASStackLayoutJustifyContent)justifyContent alignItems:(ASStackLayoutAlignItems)alignItems flexWrap:(ASStackLayoutFlexWrap)flexWrap alignContent:(ASStackLayoutAlignContent)alignContent lineSpacing:(CGFloat)lineSpacing children:(NSArray *)children
 {
   if (!(self = [super init])) {
     return nil;
@@ -73,6 +78,7 @@
   _justifyContent = justifyContent;
   _flexWrap = flexWrap;
   _alignContent = alignContent;
+  _lineSpacing = lineSpacing;
   
   [self setChildren:children];
   return self;
@@ -144,7 +150,7 @@
     return {child, style, style.size};
   });
   
-  const ASStackLayoutSpecStyle style = {.direction = _direction, .spacing = _spacing, .justifyContent = _justifyContent, .alignItems = _alignItems, .flexWrap = _flexWrap, .alignContent = _alignContent};
+  const ASStackLayoutSpecStyle style = {.direction = _direction, .spacing = _spacing, .justifyContent = _justifyContent, .alignItems = _alignItems, .flexWrap = _flexWrap, .alignContent = _alignContent, .lineSpacing = _lineSpacing};
   
   const auto unpositionedLayout = ASStackUnpositionedLayout::compute(stackChildren, style, constrainedSize, _concurrent);
   const auto positionedLayout = ASStackPositionedLayout::compute(unpositionedLayout, style, constrainedSize);

Source/Private/ASCollectionLayout.mm

@@ -87,12 +87,9 @@ static const ASScrollDirection kASStaticScrollDirection = (ASScrollDirectionRigh
 + (ASCollectionLayoutState *)calculateLayoutWithContext:(ASCollectionLayoutContext *)context
 {
   if (context.elements == nil) {
-    return [[ASCollectionLayoutState alloc] initWithContext:context
+    return [[ASCollectionLayoutState alloc] initWithContext:context];
-                                                contentSize:CGSizeZero
-                             elementToLayoutAttributesTable:[NSMapTable elementToLayoutAttributesTable]];
   }
 
-  ASDisplayNodeAssertTrue([context.layoutDelegateClass conformsToProtocol:@protocol(ASCollectionLayoutDelegate)]);
   ASCollectionLayoutState *layout = [context.layoutDelegateClass calculateLayoutWithContext:context];
   [context.layoutCache setLayout:layout forContext:context];
 

Source/Private/Layout/ASStackLayoutSpecUtilities.h

@@ -24,6 +24,7 @@ typedef struct {
   ASStackLayoutAlignItems alignItems;
   ASStackLayoutFlexWrap flexWrap;
   ASStackLayoutAlignContent alignContent;
+  CGFloat lineSpacing;
 } ASStackLayoutSpecStyle;
 
 inline CGFloat stackDimension(const ASStackLayoutDirection direction, const CGSize size)

Source/Private/Layout/ASStackPositionedLayout.mm

@@ -160,6 +160,7 @@ ASStackPositionedLayout ASStackPositionedLayout::compute(const ASStackUnposition
   const auto numOfLines = lines.size();
   const auto direction = style.direction;
   const auto alignContent = style.alignContent;
+  const auto lineSpacing = style.lineSpacing;
   const auto justifyContent = style.justifyContent;
   const auto crossViolation = ASStackUnpositionedLayout::computeCrossViolation(layout.crossDimensionSum, style, sizeRange);
   CGFloat crossOffset;
@@ -171,7 +172,7 @@ ASStackPositionedLayout ASStackPositionedLayout::compute(const ASStackUnposition
   BOOL first = YES;
   for (const auto &line : lines) {
     if (!first) {
-      p = p + directionPoint(direction, 0, crossSpacing);
+      p = p + directionPoint(direction, 0, crossSpacing + lineSpacing);
     }
     first = NO;
     

Source/Private/Layout/ASStackUnpositionedLayout.mm

@@ -113,9 +113,12 @@ static void dispatchApplyIfNeeded(size_t iterationCount, BOOL forced, void(^work
 
  @param lines unpositioned lines
  */
-static CGFloat computeLinesCrossDimensionSum(const std::vector<ASStackUnpositionedLine> &lines)
+static CGFloat computeLinesCrossDimensionSum(const std::vector<ASStackUnpositionedLine> &lines,
+                                             const ASStackLayoutSpecStyle &style)
 {
-  return std::accumulate(lines.begin(), lines.end(), 0.0,
+  return std::accumulate(lines.begin(), lines.end(),
+                         // Start from default spacing between each line:
+                         lines.empty() ? 0 : style.lineSpacing * (lines.size() - 1),
                          [&](CGFloat x, const ASStackUnpositionedLine &l) {
                            return x + l.crossSize;
                          });
@@ -236,7 +239,7 @@ static void stretchLinesAlongCrossDimension(std::vector<ASStackUnpositionedLine>
 {
   ASDisplayNodeCAssertFalse(lines.empty());
   const std::size_t numOfLines = lines.size();
-  const CGFloat violation = ASStackUnpositionedLayout::computeCrossViolation(computeLinesCrossDimensionSum(lines), style, sizeRange);
+  const CGFloat violation = ASStackUnpositionedLayout::computeCrossViolation(computeLinesCrossDimensionSum(lines, style), style, sizeRange);
   // Don't stretch if the stack is single line, because the line's cross size was clamped against the stack's constrained size.
   const BOOL shouldStretchLines = (numOfLines > 1
                                    && style.alignContent == ASStackLayoutAlignContentStretch
@@ -648,7 +651,8 @@ static std::vector<ASStackUnpositionedLine> collectChildrenIntoLines(const std::
   for(auto it = items.begin(); it != items.end(); ++it) {
     const auto &item = *it;
     const CGFloat itemStackDimension = stackDimension(style.direction, item.layout.size);
-    const BOOL negativeViolationIfAddItem = (ASStackUnpositionedLayout::computeStackViolation(lineStackDimensionSum + itemStackDimension, style, sizeRange) < 0);
+    const CGFloat itemAndSpacingStackDimension = (lineItems.empty() ? 0.0 : style.spacing) + item.child.style.spacingBefore + itemStackDimension + item.child.style.spacingAfter;
+    const BOOL negativeViolationIfAddItem = (ASStackUnpositionedLayout::computeStackViolation(lineStackDimensionSum + itemAndSpacingStackDimension, style, sizeRange) < 0);
     const BOOL breakCurrentLine = negativeViolationIfAddItem && !lineItems.empty();
     
     if (breakCurrentLine) {
@@ -658,7 +662,7 @@ static std::vector<ASStackUnpositionedLine> collectChildrenIntoLines(const std::
     }
     
     lineItems.push_back(std::move(item));
-    lineStackDimensionSum += itemStackDimension;
+    lineStackDimensionSum += itemAndSpacingStackDimension;
   }
   
   // Handle last line
@@ -752,7 +756,7 @@ ASStackUnpositionedLayout ASStackUnpositionedLayout::compute(const std::vector<A
   }
   // Compute cross dimension sum of the stack.
   // This should be done before `lines` are moved to a new ASStackUnpositionedLayout struct (i.e `std::move(lines)`)
-  CGFloat layoutCrossDimensionSum = computeLinesCrossDimensionSum(lines);
+  CGFloat layoutCrossDimensionSum = computeLinesCrossDimensionSum(lines, style);
   
   return {.lines = std::move(lines), .stackDimensionSum = layoutStackDimensionSum, .crossDimensionSum = layoutCrossDimensionSum};
 }

docs/_docs/adoption-guide-2-0-beta1.md

@@ -96,7 +96,7 @@ Texture's collection and table APIs have been moved from the view space (`collec
 
 - Search your project for `tableView` and `collectionView`. Most, if not all, of the data source / delegate methods have new node versions. 
 
-It is important that developers using Texture understand that an ASCollectionNode is backed by an ASCollectionView (a subclass of UICollectionView). ASCollectionNode runs asynchronously, so calling number -numberOfRowsInSection on the collectionNode is different than calling it on the collectionView. 
+It is important that developers using Texture understand that an ASCollectionNode is backed by an ASCollectionView (a subclass of UICollectionView). ASCollectionNode runs asynchronously, so calling -numberOfRowsInSection on the collectionNode is different than calling it on the collectionView. 
 
 For example, let's say you have an empty table. You insert `100` rows and then immediately call -tableView:numberOfRowsInSection. This will return `0` rows. If you call -waitUntilAllUpdatesAreCommitted after insertion (waits until the collectionNode synchronizes with the collectionView), you will get 100, _but_ you might block the main thread. A good developer should rarely (or never) need to use -waitUntilAllUpdatesAreCommitted. If you update the collectionNode and then need to read back immediately, you should use the collectionNode API. You shouldn't need to talk to the collectionView.  
 
@@ -122,7 +122,7 @@ Other updates include:
 
 - Renamed `pagerNode:constrainedSizeForNodeAtIndexPath:` to `pagerNode:constrainedSizeForNodeAtIndex:`
 
-- collection view update validation assertions are now enabled. If you see something like `"Invalid number of items in section 2. The number of items after the update (7) must be equal to the number of items before the update (4) plus or minus the number of items inserted or removed from the section (4 inserted, 0 removed)”`, please check the data source logic. If you have any questions, reach out to us on GitHub. 
+- collection view update validation assertions are now enabled. If you see something like `"Invalid number of items in section 2. The number of items after the update (7) must be equal to the number of items before the update (4) plus or minus the number of items inserted or removed from the section (4 inserted, 0 removed)"`, please check the data source logic. If you have any questions, reach out to us on GitHub. 
 
 Best Practices:
 

docs/_docs/image-modification-block.md

@@ -20,7 +20,7 @@ _backgroundImageNode.imageModificationBlock = ^(UIImage *image) {
 		tintColor:[UIColor colorWithWhite:0.5 alpha:0.3]
 		saturationDeltaFactor:1.8
 		maskImage:nil];
-	return newImage ? newImage : image;
+	return newImage ?: image;
 };
 
 //some time later...

docs/_docs/scroll-node.md

@@ -76,6 +76,3 @@ scrollNode.layoutSpecBlock = { node, constrainedSize in
 </pre>
 </div>
 </div>
-
-As you can see, the `scrollNode`'s underlying view is a `ASScrollNode`.
-

docs/_docs/subclassing.md

@@ -19,7 +19,7 @@ The most important thing to remember is that your init method must be capable of
 
 ### `-didLoad`
 
-This method is conceptually similar to UIViewController's `-viewDidLoad` method and is the point where the backing view has been loaded.  It is guaranteed to be called on the **main thread** and is the appropriate place to do any UIKit things (such as adding gesture recognizers, touching the view / layer, initializing UIKIt objects). 
+This method is conceptually similar to UIViewController's `-viewDidLoad` method; it’s called once and is the point where the backing view has been loaded.  It is guaranteed to be called on the **main thread** and is the appropriate place to do any UIKit things (such as adding gesture recognizers, touching the view / layer, initializing UIKIt objects). 
 
 ### `-layoutSpecThatFits:`
 

examples/ASCollectionView/Sample/ViewController.m

@@ -23,7 +23,7 @@
 
 #define ASYNC_COLLECTION_LAYOUT 0
 
-@interface ViewController () <ASCollectionDataSource, ASCollectionDelegateFlowLayout>
+@interface ViewController () <ASCollectionDataSource, ASCollectionDelegateFlowLayout, ASCollectionGalleryLayoutSizeProviding>
 
 @property (nonatomic, strong) ASCollectionNode *collectionNode;
 @property (nonatomic, strong) NSArray *data;
@@ -47,8 +47,8 @@
   [super viewDidLoad];
 
 #if ASYNC_COLLECTION_LAYOUT
-  id<ASCollectionLayoutDelegate> layoutDelegate = [[ASCollectionGalleryLayoutDelegate alloc] initWithScrollableDirections:ASScrollDirectionVerticalDirections
+  ASCollectionGalleryLayoutDelegate *layoutDelegate = [[ASCollectionGalleryLayoutDelegate alloc] initWithScrollableDirections:ASScrollDirectionVerticalDirections];
-                                                                                                                 itemSize:CGSizeMake(180, 90)];
+  layoutDelegate.sizeProvider = self;
   self.collectionNode = [[ASCollectionNode alloc] initWithLayoutDelegate:layoutDelegate layoutFacilitator:nil];
 #else
   UICollectionViewFlowLayout *layout = [[UICollectionViewFlowLayout alloc] init];
@@ -108,6 +108,14 @@
   [self.collectionNode reloadData];
 }
 
+#pragma mark - ASCollectionGalleryLayoutSizeProviding
+
+- (CGSize)sizeForElements:(ASElementMap *)elements
+{
+  ASDisplayNodeAssertMainThread();
+  return CGSizeMake(180, 90);
+}
+
 #pragma mark - ASCollectionView Data Source
 
 - (ASCellNodeBlock)collectionNode:(ASCollectionNode *)collectionNode nodeBlockForItemAtIndexPath:(NSIndexPath *)indexPath;

examples/CustomCollectionView/Sample/MosaicCollectionLayoutDelegate.m

@@ -36,11 +36,13 @@
 
 - (ASScrollDirection)scrollableDirections
 {
+  ASDisplayNodeAssertMainThread();
   return ASScrollDirectionVerticalDirections;
 }
 
 - (id)additionalInfoForLayoutWithElements:(ASElementMap *)elements
 {
+  ASDisplayNodeAssertMainThread();
   return _info;
 }