[ASCollectionView] Improve performance and behavior of rotation / bounds changes.

CHANGELOG.md

@@ -1,6 +1,7 @@
 ## master
 
 * Add your own contributions to the next release on the line below this with your name.
+- [ASCollectionView] Improve performance and behavior of rotation / bounds changes. [Scott Goodson](https://github.com/appleguy) [#431](https://github.com/TextureGroup/Texture/pull/431)
 - [ASCollectionView] Improve index space translation of Flow Layout Delegate methods. [Scott Goodson](https://github.com/appleguy)
 - [ASVideoNode] Fix unreleased time observer. [Flo Vouin](https://github.com/flovouin)
 - [PINCache] Set a default .byteLimit to reduce disk usage and startup time. [#595](https://github.com/TextureGroup/Texture/pull/595) [Scott Goodson](https://github.com/appleguy)

Source/ASCollectionView.mm

@@ -367,7 +367,9 @@ - (void)scrollToItemAtIndexPath:(NSIndexPath *)indexPath atScrollPosition:(UICol
 
 - (void)relayoutItems
 {
-  [_dataController relayoutAllNodes];
+  [_dataController relayoutAllNodesWithInvalidationBlock:^{
+    [self.collectionViewLayout invalidateLayout];
+  }];
 }
 
 - (BOOL)isProcessingUpdates
@@ -2271,10 +2273,9 @@ - (void)layer:(CALayer *)layer didChangeBoundsWithOldValue:(CGRect)oldBounds new
   BOOL changedInNonScrollingDirection = (fixedHorizontally && newBounds.size.width != lastUsedSize.width) || (fixedVertically && newBounds.size.height != lastUsedSize.height);
 
   if (changedInNonScrollingDirection) {
-    [_dataController relayoutAllNodes];
-    [_dataController waitUntilAllUpdatesAreProcessed];
-    // We need to ensure the size requery is done before we update our layout.
-    [self.collectionViewLayout invalidateLayout];
+    [_dataController relayoutAllNodesWithInvalidationBlock:^{
+      [self.collectionViewLayout invalidateLayout];
+    }];
   }
 }
 

Source/ASTableView.mm

@@ -553,7 +553,7 @@ - (void)scrollToRowAtIndexPath:(NSIndexPath *)indexPath atScrollPosition:(UITabl
 
 - (void)relayoutItems
 {
-  [_dataController relayoutAllNodes];
+  [_dataController relayoutAllNodesWithInvalidationBlock:nil];
 }
 
 - (void)setTuningParameters:(ASRangeTuningParameters)tuningParameters forRangeType:(ASLayoutRangeType)rangeType
@@ -760,7 +760,7 @@ - (void)layoutSubviews
     _nodesConstrainedWidth = constrainedWidth;
 
     [self beginUpdates];
-    [_dataController relayoutAllNodes];
+    [_dataController relayoutAllNodesWithInvalidationBlock:nil];
     [self endUpdatesAnimated:(ASDisplayNodeLayerHasAnimations(self.layer) == NO) completion:nil];
   } else {
     if (_cellsForLayoutUpdates.count > 0) {

Source/Details/ASDataController.h

@@ -244,8 +244,11 @@ extern NSString * const ASCollectionInvalidUpdateException;
  * 
  * @discussion Used to respond to a change in size of the containing view
  * (e.g. ASTableView or ASCollectionView after an orientation change).
+ *
+ * The invalidationBlock is called after flushing the ASMainSerialQueue, which ensures that any in-progress
+ * layout calculations have been applied. The block will not be called if data hasn't been loaded.
  */
-- (void)relayoutAllNodes;
+- (void)relayoutAllNodesWithInvalidationBlock:(nullable void (^)())invalidationBlock;
 
 /**
  * Re-measures given nodes in the backing store.

Source/Details/ASDataController.mm

@@ -759,7 +759,7 @@ - (void)relayoutNodes:(id<NSFastEnumeration>)nodes nodesSizeChanged:(NSMutableAr
   }
 }
 
-- (void)relayoutAllNodes
+- (void)relayoutAllNodesWithInvalidationBlock:(nullable void (^)())invalidationBlock
 {
   ASDisplayNodeAssertMainThread();
   if (!_initialReloadDataHasBeenCalled) {
@@ -770,6 +770,13 @@ - (void)relayoutAllNodes
   // i.e there might be some nodes that were measured using the old constrained size but haven't been added to _visibleMap
   LOG(@"Edit Command - relayoutRows");
   [self _scheduleBlockOnMainSerialQueue:^{
+    // Because -invalidateLayout doesn't trigger any operations by itself, and we answer queries from UICollectionView using layoutThatFits:,
+    // we invalidate the layout before we have updated all of the cells. Any cells that the collection needs the size of immediately will get
+    // -layoutThatFits: with a new constraint, on the main thread, and synchronously calculate them. Meanwhile, relayoutAllNodes will update
+    // the layout of any remaining nodes on background threads (and fast-return for any nodes that the UICV got to first).
+    if (invalidationBlock) {
+      invalidationBlock();
+    }
     [self _relayoutAllNodes];
   }];
 }

Tests/ASTableViewTests.mm

@@ -37,10 +37,10 @@ @interface ASTestDataController : ASDataController
 
 @implementation ASTestDataController
 
-- (void)relayoutAllNodes
+- (void)relayoutAllNodesWithInvalidationBlock:(nullable void (^)())invalidationBlock
 {
   _numberOfAllNodesRelayouts++;
-  [super relayoutAllNodes];
+  [super relayoutAllNodesWithInvalidationBlock:invalidationBlock];
 }
 
 @end