Question

I have a UISearchBar that is hooked up with a NSFetchedResultsController.

It searches as the user enters text into the search bar. I notice for the first few letters it lags, but then it quickens up and their is no lag. Is there any way to reduce the initial lag and make the search very snappy?

- (void)filterResultsUsingString:(NSString *)filterString {
    self.billingSearchText = filterString;      

    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:YES];
    NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];
    [fetchRequest setSortDescriptors:sortDescriptors];
    NSEntityDescription *entity = nil;
    if ([self.billingSearchCategory isEqualToString:@"icd9"]) {
         entity = [NSEntityDescription entityForName:@"ICD9" inManagedObjectContext:managedObjectContext];
    }
    else if ([self.billingSearchCategory isEqualToString:@"cpt"]) {
        entity = [NSEntityDescription entityForName:@"CPT" inManagedObjectContext:managedObjectContext];
    }

    [fetchRequest setEntity:entity];
    [sortDescriptors release];
    [sortDescriptor release];

    self.fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:managedObjectContext sectionNameKeyPath:nil cacheName:@"Root"];

    [fetchRequest release];
    NSPredicate *predicate =[NSPredicate predicateWithFormat:@"(name contains[cd] %@) OR (code contains[cd] %@)", self.billingSearchText, self.billingSearchText];
    [self.fetchedResultsController.fetchRequest setPredicate:predicate];
    NSError *error = nil;
    if (![[self fetchedResultsController] performFetch:&error]) 
    {
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        exit(-1);  // Fail
    } 

    [self.tableView reloadData];
}

Answer 1

Based on the code youve posted I can see that you create a new FetchedResultsController each time the user changes the search string. That means that it is not the creation of the FRC thats causing the lag.

Are you running the search query on the mainthread?
That could be one reason for the lag.
And that could also explain the first query lagging more than the subsequent ones. It might be because the query runs faster as the search string gets longer and possible results are narrowed down (and require less processing time).

Id suggest that you implement a solution that waits 0.1-0.3 seconds after each keypress before performing a search. This reduces unnecessary search queries as the user types longer queries. And I would advice you to perform the search in a separate thread to avoid locking the GUI during the search. When the search thread is finished, you perform a callback to the mainthread and update the screen with the results.