#define kBgQueue dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,0)

-(void)searchBar:(UISearchBar*)searchBar textDidChange:(NSString*)text
{
    if(text.length == 0)
    {
        jsonResults = nil;
        [self.tableView reloadData];
    }
    else
    {
        jsonResults = nil;
        [self.tableView reloadData];
        NSURL *searchUrl = [NSURL URLWithString:[NSString stringWithFormat:@"https://itunes.apple.com/search?term=%@&country=gb&entity=software",text]];
         dispatch_async(kBgQueue, ^{
         NSData* data = [NSData dataWithContentsOfURL:searchUrl];
         [self performSelectorOnMainThread:@selector(fetchedData:)
         withObject:data waitUntilDone:NO];
         });
    }
}


-(void)fetchedData:(NSData *)responseData{
    NSError* error;
    NSDictionary* json = [NSJSONSerialization
                          JSONObjectWithData:responseData
                          options:kNilOptions
                          error:&error];
    jsonResults = [json objectForKey:@"results"];
    [self.tableView reloadData];
}

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    //Do the computing-research

     dispatch_async(dispatch_get_main_queue(), ^{
        //do UI update here
    });
});