AutoCompleteTableView responding very slow - objective-c

Question

I'm trying to access my web service for getting string from there and plae it into my AutoCompleteTableView with below method -
- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
NSString *substring = [NSString stringWithString:txtSearching.text];
substring = [substring stringByReplacingCharactersInRange:range withString:string];
if (([substring isEqualToString:#""]) || (substring == nil) || ([substring length] == 0)){
autoCompleteTableView.hidden=YES;
}
NSString *jsonUrl = [NSString stringWithFormat:MYAPI,substring];
NSURL *url = [NSURL URLWithString:[jsonUrl stringByReplacingOccurrencesOfString:#" " withString:#"%20"]];
NSData *jsonData = [NSData dataWithContentsOfURL:url];
NSArray *data = [jsonData objectFromJSONData];
for (int i = 0; i< [data count]; i++) {
NSDictionary * dic = [data objectAtIndex:i];
[elementArray addObject:[dic objectForKey:#"keyword"]];
}
[self searchAutocompleteEntriesWithSubstring:substring];
[elementArray removeAllObjects];
return YES;
}
And, my searchAutocompleteEntriesWithSubstring
- (void)searchAutocompleteEntriesWithSubstring:(NSString *)substring {
// Put anything that starts with this substring into the autoCompleteArray
// The items in this array is what will show up in the table view
//[elementArray removeAllObjects];
[autoCompleteArray removeAllObjects];
int lengthOfSubstring = [substring length];
for(NSString *curString in elementArray) {
int lengthOfCurentString = [curString length];
if (lengthOfCurentString >=lengthOfSubstring) {
NSString *substringRangeLowerCase = [[curString substringWithRange:NSMakeRange(0,[substring length])] lowercaseString];
NSString *substringRangeUpperCase = [[curString substringWithRange:NSMakeRange(0,[substring length])] uppercaseString];
NSString *substringRangeCase = [[curString substringWithRange:NSMakeRange(0,[substring length])] capitalizedString];
if (([substring isEqualToString:#""]) || (substring == nil) || ([substring length] == 0)) {
// NSLog(#"current string = [%#]",curString);
}else{
if (([substring isEqualToString:substringRangeLowerCase]) || ([substring isEqualToString:substringRangeUpperCase]) || ([substring isEqualToString:substringRangeCase])) {
[autoCompleteArray addObject:curString];
}
}
}
}
autoCompleteTableView.hidden = NO;
[autoCompleteTableView reloadData];
}
My data-
[{"keyword":"qwerty"},{"keyword":"question paper judicial"},{"keyword":"qwe"},{"keyword":"quilts"},{"keyword":"quinoa"},{"keyword":"qwerty0disk"},{"keyword":"q"}]
I don't know why my UI getting very slow.. Am using JSONKit also.

Answer 1

NSData *jsonData = [NSData dataWithContentsOfURL:url]; is a synchronous call.
It means that the call is done in the main thread and it will block the execution during its process. If the connection is slow, it will block the interface (which runs in the main thread as well) until it receives datas.
In order to avoid blocking your interface while dataWithContentOfURL finish, you should use gcd or implement an asynchronous class to fetch the data.
Here is a discussion about gcd and asynchronous connections
I hope this will help.