Switch to using maptables to track some metadata bout items so that we can match items up when we need to find them by indexPath or point. Remove uneeded ivar from layout. Add call to delegate when selecting item

Source/NSCollectionView.m

@@ -162,9 +162,9 @@ static NSString *placeholderItem = nil;
   _indexPathsForVisibleItems = [[NSMutableSet alloc] init];
   _visibleSupplementaryViews = [[NSMutableDictionary alloc] init];
   _indexPathsForSupplementaryElementsOfKind = [[NSMutableSet alloc] init];
-  _itemsToAttributes = [[NSMutableDictionary alloc] init];
-  _itemsToIndexPaths = RETAIN([NSMapTable weakToWeakObjectsMapTable]);
-  _indexPathsToItems = RETAIN([NSMapTable weakToWeakObjectsMapTable]);
+  _itemsToAttributes = RETAIN([NSMapTable strongToStrongObjectsMapTable]);
+  _itemsToIndexPaths = RETAIN([NSMapTable strongToStrongObjectsMapTable]);
+  _indexPathsToItems = RETAIN([NSMapTable strongToStrongObjectsMapTable]);
   
   // Registered nib/class
   _registeredNibs = RETAIN([NSMapTable weakToStrongObjectsMapTable]);
@@ -1418,9 +1418,25 @@ static NSString *placeholderItem = nil;
 
 - (NSIndexPath *) indexPathForItemAtPoint: (NSPoint)point
 {
-  NSInteger row = floor(point.y / (_itemSize.height + _verticalMargin));
-  NSInteger column = floor(point.x / (_itemSize.width + _horizontalMargin));
-  NSIndexPath *p = [NSIndexPath indexPathForRow: row inSection: column];
+  NSIndexPath *p = nil;
+  NSEnumerator *ke = [_itemsToAttributes keyEnumerator];
+  NSCollectionViewItem *item = nil;
+
+  while ((item = [ke nextObject]) != nil)
+    {
+      NSCollectionViewLayoutAttributes *attr = [_itemsToAttributes objectForKey: item];
+
+      if (attr != nil)
+        {
+          NSRect f = [attr frame];
+          
+          if (NSPointInRect(point, f))
+            {
+              p = [self indexPathForItem: item];
+              break;
+            }
+        }
+    }
 
   return p;
 }