UITableView cellForRowAtIndexPath gets called to early

I have a UITableView that loads its array items fine on the first call. However when i refresh the tableview it crashes because the delegate method cellForRowAtIndexPath gets called to early. I have an integer which represents the index of my main data array and this gets reset to 0 in my refresh button. However its crashing because its trying to reload the data before its been reset. I would normally use indexPath.row as my index however the array is complicated and the indexPath.row will not match up to what i want to show for each cell. Heres some code, any help is appreciated.

This gets called when i pull down to refresh AND in viewDidLoad to prepare the data

- (IBAction)refresh:(id)sender {
itemIndexer = 0;
[sender beginRefreshing];
[self loadData];
}

Part of my loadData method

-(void) loadData {
dispatch_queue_t backgroundQueue = dispatch_queue_create("com.Foo.myqueue", 0);
dispatch_queue_t mainQueue = dispatch_get_main_queue();

dispatch_async(backgroundQueue, ^{

   [self downloadData];

    dispatch_async(mainQueue, ^{
            [self.tableView reloadData];
            [_rcRefresh endRefreshing];
    });
});

In viewDidLoad i call to initially load the tableview:

[self refresh:_rcRefresh];

I am getting a index outside bounds of array error. Which i have used breakpoints to determine why, the reason is simply because the refresh isn't getting called at all otherwise itemIndexer would be set to 0. Instead its a number 1 greater than the array size. If its really necessary i can post cellForRowAtIndexPath however I'm unsure if you need it if it works on the first call. So to summarise the first call to the tableview works and the data is loaded fine however the refresh causes the index to be outside the bounds of the array as if refresh: is never called.

Solution

For what you say, I can only try guessing:

Your numberOfSectionsInTableView/numberOfRowsInSection is returning a wrong number.
If [self downloadData] is asynchronous (you are making a server request and not waiting for the response), you should reloadData once you have the data.
The data you download is not merged properly with the data you already have.

Some more code (numberOfSectionsInTableView, numberOfRowsInSection, cellForRowAtIndexPath, downloadData) would definitely help.