rkeniger · November 28, 2013 04:33 · Nov 28, 2013
diff --git a/gistfile1.m b/gistfile1.m
@@ -0,0 +1,66 @@
+- (CGPoint)targetContentOffsetForProposedContentOffset:(CGPoint)proposedContentOffset withScrollingVelocity:(CGPoint)velocity
+{
+	CGFloat offSetAdjustment = MAXFLOAT;
+	CGFloat horizontalCenter = (CGFloat) (proposedContentOffset.x + (self.collectionView.bounds.size.width / 2.0));
+
+	CGRect targetRect = CGRectMake(proposedContentOffset.x, 0.0, self.collectionView.bounds.size.width, self.collectionView.bounds.size.height);
+
+	NSArray *array = [self layoutAttributesForElementsInRect:targetRect];
+	for (UICollectionViewLayoutAttributes *layoutAttributes in array)
+	{
+		if(layoutAttributes.representedElementCategory == UICollectionElementCategoryCell)
+		{
+			CGFloat itemHorizontalCenter = layoutAttributes.center.x;
+			if (ABS(itemHorizontalCenter - horizontalCenter) < ABS(offSetAdjustment))
+			{
+				offSetAdjustment = itemHorizontalCenter - horizontalCenter;
+			}
+		}
+	}
+
+	CGFloat nextOffset = proposedContentOffset.x + offSetAdjustment;
+
+	do {
+		proposedContentOffset.x = nextOffset;
+		CGFloat deltaX = proposedContentOffset.x - self.collectionView.contentOffset.x;
+		CGFloat velX = velocity.x;
+
+		if(deltaX == 0.0 || velX == 0 || (velX > 0.0 && deltaX > 0.0) || (velX < 0.0 && deltaX < 0.0))
+		{
+			break;
+		}
+
+		if(velocity.x > 0.0)
+		{
+			nextOffset += [self snapStep];
+		}
+		else if(velocity.x < 0.0)
+		{
+			nextOffset -= [self snapStep];
+		}
+	} while ([self isValidOffset:nextOffset]);
+
+	proposedContentOffset.y = 0.0;
+
+	return proposedContentOffset;
+}
+
+- (BOOL)isValidOffset:(CGFloat)offset
+{
+    return (offset >= [self minContentOffset] && offset <= [self maxContentOffset]);
+}
+
+- (CGFloat)minContentOffset
+{
+    return -self.collectionView.contentInset.left;
+}
+
+- (CGFloat)maxContentOffset
+{
+	return [self minContentOffset] + self.collectionView.contentSize.width - self.itemSize.width;
+}
+
+- (CGFloat)snapStep
+{
+	return self.itemSize.width + self.minimumLineSpacing;
+}