ASCollectionLayout improvements

- During the first layout calculation, measure more than just elements in the visible viewport. - Remove unnecessary params in `-[ASCollectionLayoutState getAndRemoveUnmeasuredLayoutAttributesPageTableInRect`.]
TextureGroup · Aug 17, 2017 · 1f6488a · 1f6488a
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Showing 4 changed files with 14 additions and 13 deletions.
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -7,7 +7,7 @@
 - Negate iOS 11 automatic estimated table row heights. [Christian Selig](https://github.com/christianselig) [#485](https://github.com/TextureGroup/Texture/pull/485)
 - [Breaking] Add content offset bridging property to ASTableNode and ASCollectionNode. Deprecate related methods in ASTableView and ASCollectionView [Huy Nguyen](https://github.com/nguyenhuy) [#460](https://github.com/TextureGroup/Texture/pull/460)
 - Remove re-entrant access to self.view when applying initial pending state. [Adlai Holler](https://github.com/Adlai-Holler) [#510](https://github.com/TextureGroup/Texture/pull/510)
-- Small improvements in ASCollectionLayout [Huy Nguyen](https://github.com/nguyenhuy) [#509](https://github.com/TextureGroup/Texture/pull/509)
+- Small improvements in ASCollectionLayout [Huy Nguyen](https://github.com/nguyenhuy) [#509](https://github.com/TextureGroup/Texture/pull/509) [#513](https://github.com/TextureGroup/Texture/pull/513)
 
 ##2.4
 - Fix an issue where inserting/deleting sections could lead to inconsistent supplementary element behavior. [Adlai Holler](https://github.com/Adlai-Holler)

diff --git a/Source/Details/ASCollectionLayoutState.mm b/Source/Details/ASCollectionLayoutState.mm
@@ -170,9 +170,10 @@ - (UICollectionViewLayoutAttributes *)layoutAttributesForElement:(ASCollectionEl
 }
 
 - (ASPageToLayoutAttributesTable *)getAndRemoveUnmeasuredLayoutAttributesPageTableInRect:(CGRect)rect
-                                                                             contentSize:(CGSize)contentSize
-                                                                                pageSize:(CGSize)pageSize
 {
+  CGSize pageSize = _context.viewportSize;
+  CGSize contentSize = _contentSize;
+
   ASDN::MutexLocker l(__instanceLock__);
   if (_unmeasuredPageToLayoutAttributesTable.count == 0 || CGRectIsNull(rect) || CGRectIsEmpty(rect) || CGSizeEqualToSize(CGSizeZero, contentSize) || CGSizeEqualToSize(CGSizeZero, pageSize)) {
     return nil;

diff --git a/Source/Private/ASCollectionLayout.mm b/Source/Private/ASCollectionLayout.mm
@@ -93,15 +93,19 @@ + (ASCollectionLayoutState *)calculateLayoutWithContext:(ASCollectionLayoutConte
   ASCollectionLayoutState *layout = [context.layoutDelegateClass calculateLayoutWithContext:context];
   [context.layoutCache setLayout:layout forContext:context];
 
-  // Measure elements in the measure range ahead of time, block on the initial rect as it'll be visible shortly
+  // Measure elements in the measure range ahead of time
   CGSize viewportSize = context.viewportSize;
   CGPoint contentOffset = context.initialContentOffset;
   CGRect initialRect = CGRectMake(contentOffset.x, contentOffset.y, viewportSize.width, viewportSize.height);
   CGRect measureRect = CGRectExpandToRangeWithScrollableDirections(initialRect,
                                                                    kASDefaultMeasureRangeTuningParameters,
                                                                    context.scrollableDirections,
                                                                    kASStaticScrollDirection);
-  [self _measureElementsInRect:measureRect blockingRect:initialRect layout:layout];
+  // The first call to -layoutAttributesForElementsInRect: will be with a rect that is way bigger than initialRect here.
+  // If we only block on initialRect, a few elements that are outside of initialRect but inside measureRect
+  // may not be available by the time -layoutAttributesForElementsInRect: is called.
+  // Since this method is usually run off main, let's spawn more threads to measure and block on all elements in measureRect.
+  [self _measureElementsInRect:measureRect blockingRect:measureRect layout:layout];
 
   return layout;
 }
@@ -248,18 +252,16 @@ + (void)_measureElementsInRect:(CGRect)rect blockingRect:(CGRect)blockingRect la
   }
 
   // Step 2: Get layout attributes of all elements within the specified outer rect
-  ASCollectionLayoutContext *context = layout.context;
-  CGSize pageSize = context.viewportSize;
-  ASPageToLayoutAttributesTable *attrsTable = [layout getAndRemoveUnmeasuredLayoutAttributesPageTableInRect:rect
-                                                                                                contentSize:contentSize
-                                                                                                   pageSize:pageSize];
+  ASPageToLayoutAttributesTable *attrsTable = [layout getAndRemoveUnmeasuredLayoutAttributesPageTableInRect:rect];
   if (attrsTable.count == 0) {
     // No elements in this rect! Bail early
     return;
   }
 
   // Step 3: Split all those attributes into blocking and non-blocking buckets
   // Use ordered sets here because some items may span multiple pages, and the sets will be accessed by indexes later on.
+  ASCollectionLayoutContext *context = layout.context;
+  CGSize pageSize = context.viewportSize;
   NSMutableOrderedSet<UICollectionViewLayoutAttributes *> *blockingAttrs = hasBlockingRect ? [NSMutableOrderedSet orderedSet] : nil;
   NSMutableOrderedSet<UICollectionViewLayoutAttributes *> *nonBlockingAttrs = [NSMutableOrderedSet orderedSet];
   for (id pagePtr in attrsTable) {

diff --git a/Source/Private/ASCollectionLayoutState+Private.h b/Source/Private/ASCollectionLayoutState+Private.h
@@ -22,9 +22,7 @@ NS_ASSUME_NONNULL_BEGIN
  *
  * @discussion This method is atomic and thread-safe
  */
-- (nullable ASPageToLayoutAttributesTable *)getAndRemoveUnmeasuredLayoutAttributesPageTableInRect:(CGRect)rect
-                                                                                      contentSize:(CGSize)contentSize
-                                                                                         pageSize:(CGSize)pageSize;
+- (nullable ASPageToLayoutAttributesTable *)getAndRemoveUnmeasuredLayoutAttributesPageTableInRect:(CGRect)rect;
 
 @end