Unexpected KVO Crash

I have a UITableView whose height changes at runtime: an application loads images and then displays them in a TableView. I applied pull to update as a function for the footer of my table view.

Since the row height is not constant, I added an observer to my UITableView:

[self.tableView addObserver:_refreshFooter
                 forKeyPath:@"contentSize"
                    options:NSKeyValueObservingOptionNew
                    context:NULL];

In my _refreshFooter , the following method is called as soon as the contentSize changes:

- (void)observeValueForKeyPath:(NSString *)keyPath
                      ofObject:(id)object
                        change:(NSDictionary *)change
                       context:(void *)context
{
  UITableView *tbV = object;

  float realBottom = MAX(tbV.frame.size.height, tbV.contentSize.height);
  self.frame = CGRectMake(self.frame.origin.x,
                          realBottom,
                          self.frame.size.width,
                          self.frame.size.height);
}

, TableViewController. iPhone 4 4S 5.0.1 5.1 - KVO, , , .

:

0   libobjc.A.dylib 0x3671bf78 objc_msgSend + 15
1   Foundation 0x31145659 NSKeyValuePushPendingNotificationPerThread + 68
2   Foundation 0x3113774b NSKeyValueWillChange + 414
3   Foundation 0x3110e84f -[NSObject(NSKeyValueObserverNotification) willChangeValueForKey:] + 182
4   Foundation 0x31190b23 _NSSetSizeValueAndNotify + 82
5   UIKit 0x32368f8d -[UITableView(_UITableViewPrivate) _updateContentSize] + 572
6   UIKit 0x3249cd51 -[UITableView setTableFooterView:] + 432