app crashes on fast uisearchbar text entry - ios

Question

My app shows the following error when type into a UISearchBar quickly
Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[__NSArrayI objectAtIndex:]: index 206 beyond bounds [0 .. 13]
when typing slowly, search works just fine
-(void)searchBar:(UISearchBar*)searchBar textDidChange:(NSString*)text
{
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
if(text.length == 0)
{
isFiltered = FALSE;
}
else
{
filteredTableData = [[NSMutableArray alloc] init];
sortedCustomerID= [[NSMutableArray alloc]init];
sortedDefaultsShipingID=[[NSMutableArray alloc]init];
isFiltered = true;
if (text !=nil)
{
NSPredicate *predicate =[NSPredicate predicateWithFormat:#"lastName contains[cd] %# ",text];
[fetchedResultsController.fetchRequest setPredicate:predicate];
}
else
{
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"All"];
[fetchedResultsController.fetchRequest setPredicate:predicate];
}
NSError *error = nil;
if (![[self fetchedResultsController] performFetch:&error])
{
// Handle error
NSLog(#"Unresolved error %#, %#", error, [error userInfo]);
exit(-1); // Fail
}
_fetchedObjects = fetchedResultsController.fetchedObjects;
for (int i =0 ; i<_fetchedObjects.count ; i ++)
{
[filteredTableData addObject:[[_fetchedObjects valueForKey:#"lastName"]objectAtIndex:i]];
[sortedCustomerID addObject:[[_fetchedObjects valueForKey:#"customerID"]objectAtIndex:i]];
[sortedDefaultsShipingID addObject:[[_fetchedObjects valueForKey:#"defaultShippingID"]objectAtIndex:i]];
}
}
NSLog(#" name=%# customerID=%# shippingID=%#", filteredTableData,sortedCustomerID,sortedDefaultsShipingID);
dispatch_async(dispatch_get_main_queue(), ^{
// Return data and update on the main thread
// Task 3: Deliver the data to a 3rd party component (always do on the main thread).
});
});
}

Answer 1

With most exceptions you get quite a bit of additional information that can help you figure out what is going wrong.
In this case, the exception description is telling you that you tried to access an NSArray element that does not exist. It would appear that the NSArray object in question is _fetchedObjects. Furthermore, based on the name, it would seem that it is an ivar.
So consider what is happening here. Character is entered in search bar. Async operation gets launched and data is retrieved, stored in _fetchedObjects and then accessed. However, what happens when several of these operations get created very quickly and each of them try to access the same _fetchedObjects?
I would consider storing the search results in a local variable and then assigning it to an ivar/property at the end of the async op if you really need to store it.

Answer 2

Try changing your for loop to
for (int i =0 ; i<_fetchedObjects.count ; i ++)
{
[filteredTableData addObject:[[_fetchedObjects objectAtIndex:i] valueForKey:#"lastName"]];
[sortedCustomerID addObject:[[_fetchedObjects objectAtIndex:i] valueForKey:#"customerID"]];
[sortedDefaultsShipingID addObject:[[_fetchedObjects objectAtIndex:i] valueForKey:#"defaultShippingID"]];
}