Delay asset controller layout until frame is correct and layout is complete

QBImagePicker/QBAssetsViewController.m

@@ -105,8 +105,12 @@ - (void)viewWillAppear:(BOOL)animated
 
     // Scroll to bottom
     if (self.fetchResult.count > 0 && self.isMovingToParentViewController && !self.disableScrollToBottom) {
-        NSIndexPath *indexPath = [NSIndexPath indexPathForItem:(self.fetchResult.count - 1) inSection:0];
-        [self.collectionView scrollToItemAtIndexPath:indexPath atScrollPosition:UICollectionViewScrollPositionTop animated:NO];
+        // when presenting as a .FormSheet on iPad, the frame is not correct until just after viewWillAppear:
+        // dispatching to the main thread waits one run loop until the frame is update and the layout is complete
+        dispatch_async(dispatch_get_main_queue(), ^{
+            NSIndexPath *indexPath = [NSIndexPath indexPathForItem:(self.fetchResult.count - 1) inSection:0];
+            [self.collectionView scrollToItemAtIndexPath:indexPath atScrollPosition:UICollectionViewScrollPositionTop animated:NO];
+        });
     }
 }