Update to latest state

AsyncDisplayKit/ASPagerFlowLayout.m

@@ -7,73 +7,78 @@
 //
 
 #import "ASPagerFlowLayout.h"
-#import "ASPagerNode.h"
 
 @interface ASPagerFlowLayout ()
 
 @property (strong, nonatomic) NSIndexPath *currentIndexPath;
-@property (weak, nonatomic) id<ASPagerFlowLayoutPageProvider> pageProvider;
 
 @end
 
-@implementation ASPagerFlowLayout
-
-#pragma mark - Lifecycle
-
-- (instancetype)initWithPageProvider:(id<ASPagerFlowLayoutPageProvider>)pageProvider
-{
-  self = [super init];
-  if (self == nil) { return self; }
-  _pageProvider = pageProvider;
-  return self;
+@implementation ASPagerFlowLayout {
+    BOOL _didRotate;
+    CGRect _cachedCollectionViewBounds;
 }
 
-#pragma mark - UICollectionViewFlowLayout
-
-- (BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)newBounds
+- (CGPoint)targetContentOffsetForProposedContentOffset:(CGPoint)proposedContentOffset withScrollingVelocity:(CGPoint)velocity
 {
-  CGRect oldBounds = self.collectionView.bounds;
-  if (!CGSizeEqualToSize(oldBounds.size, newBounds.size)) {
-    return YES;
-  }
+    NSInteger currentPage = ceil(proposedContentOffset.x / self.collectionView.bounds.size.width);
+    self.currentIndexPath = [NSIndexPath indexPathForItem:currentPage inSection:0];
     
-  return NO;
+    return [super targetContentOffsetForProposedContentOffset:proposedContentOffset withScrollingVelocity:velocity];
 }
 
+
+- (void)prepareForAnimatedBoundsChange:(CGRect)oldBounds
+{
+  // Cache the current page if a rotation did happen. This happens before the rotation animation
+  // is occuring and the bounds changed so we use this as an opportunity to cache the current index path
+  if (_cachedCollectionViewBounds.size.width != self.collectionView.bounds.size.width) {
+      _cachedCollectionViewBounds = self.collectionView.bounds;
+        
+    // Figurring out current page based on the old bounds visible space
+    CGRect visibleRect = oldBounds;
+           
+    CGFloat visibleXCenter = CGRectGetMidX(visibleRect);
+    NSArray<UICollectionViewLayoutAttributes *> *layoutAttributes = [self layoutAttributesForElementsInRect:visibleRect];
+    for (UICollectionViewLayoutAttributes *attributes in layoutAttributes) {
+      if ([attributes representedElementCategory] == UICollectionElementCategoryCell && attributes.center.x == visibleXCenter) {
+        self.currentIndexPath = attributes.indexPath;
+        break;
+      }
+    }
+      
+      _didRotate = YES;
+    }
+    
+    [super prepareForAnimatedBoundsChange:oldBounds];
+}
 - (CGPoint)targetContentOffsetForProposedContentOffset:(CGPoint)proposedContentOffset
+{
+    // Don't mess around if the user is interacting with the page node. Although if just a rotation happened we should
+    // try to use the current index path to not end up setting the target content offset to something in between pages
+    if (_didRotate || (!self.collectionView.isDecelerating && !self.collectionView.isTracking)) {
+        _didRotate = NO;
+        if (self.currentIndexPath) {
+            return [self _targetContentOffsetForItemAtIndexPath:self.currentIndexPath proposedContentOffset:proposedContentOffset];
+        }
+    }
+    
+    return [super targetContentOffsetForProposedContentOffset:proposedContentOffset];
+}
+
+- (CGPoint)_targetContentOffsetForItemAtIndexPath:(NSIndexPath *)indexPath proposedContentOffset:(CGPoint)proposedContentOffset
 {
   if ([self _dataSourceIsEmpty]) {
     return proposedContentOffset;
   }
   
-  if (_pageProvider == nil || [self _visibleRectIsInvalid]) {
-    return [super targetContentOffsetForProposedContentOffset:proposedContentOffset];
-  }
-
-  NSIndexPath *indexPath = [NSIndexPath indexPathForItem:_pageProvider.currentPageIndex inSection:0];
-  UICollectionViewLayoutAttributes *attributes = [self layoutAttributesForItemAtIndexPath:indexPath];
-  CGFloat xOffset = (CGRectGetWidth(self.collectionView.bounds) - CGRectGetWidth(attributes.frame)) / 2;
-  return CGPointMake(attributes.frame.origin.x - xOffset, proposedContentOffset.y);
+  CGFloat currentPageXOffset = self.currentIndexPath.item * CGRectGetWidth(self.collectionView.bounds);
+    return CGPointMake(currentPageXOffset, proposedContentOffset.y);
 }
 
-#pragma mark - Helper
-
 - (BOOL)_dataSourceIsEmpty
 {
-  return ([self.collectionView numberOfSections] == 0 || [self.collectionView numberOfItemsInSection:0] == 0);
-}
-
-- (CGRect)_visibleRect
-{
-  CGRect visibleRect;
-  visibleRect.origin = self.collectionView.contentOffset;
-  visibleRect.size = self.collectionView.bounds.size;
-  return visibleRect;
-}
-
-- (BOOL)_visibleRectIsInvalid
-{
-  return CGRectEqualToRect([self _visibleRect], CGRectZero);
+    return ([self.collectionView numberOfSections] == 0 || [self.collectionView numberOfItemsInSection:0] == 0);
 }
 
 @end