How do you properly implement async search results? - ios

Question

I made a clone of UITableView called TableView with its own dataSource and delegate that mimics the original UITableView but is intended to do some things differently. I also made a GoogleSuggest class with its own delegate that requests google autocomplete suggestions from a known URL.
The GoogleSuggest class has this method:
- (void)requestSuggestionsForText:(NSString *)text {
[NSThread detachNewThreadSelector:#selector(asyncRequestSuggestionsForText:)
toTarget:self
withObject:text];
}
When called it dispatches this private background thread:
- (void)asyncRequestSuggestionsForText:(NSString *)text;
When it receives results it calls this delegate method:
- (void)googleSuggestDidReceiveResult:(GoogleSuggestResult *)result;
Everything worked fine with little controlled experiments until I put it all together in the main ViewController.
Initially, this method returned a "UI API called on a background thread" error:
#pragma mark - GoogleSuggestDelegate
- (void)googleSuggestDidReceiveResult:(GoogleSuggestResult *)result {
_googleSuggestions = result.suggestions;
[_tableView reloadData];
}
Then I replaced the last line with this and it worked:
dispatch_async(dispatch_get_main_queue(), ^{
[self.tableView reloadData];
});
Now, I'm getting a "-[__NSCFNumber length]: unrecognized selector sent to instance 0xbbe7252cd9143595" error.
The result.suggestions is a simple NSMutableArray with NSString variables, no NSNumbers anywhere.
This works and I get to see all results logged:
- (TableViewCell *)tableView:(tableView *)tableView cellAtIndex:(NSUInteger)index {
TableViewCell *cellView = [[TableViewCell alloc] init];
NSString *result = [_googleSuggestions objectAtIndex:index];
NSLog(#"Result: %#", result);
// cellView.titleLabel.text = result;
return cellView;
}
This also works and I get to see all results logged:
- (TableViewCell *)tableView:(tableView *)tableView cellAtIndex:(NSUInteger)index {
TableViewCell *cellView = [[TableViewCell alloc] init];
NSString *result = [_googleSuggestions objectAtIndex:index];
NSLog(#"Result: %#", result);
cellView.titleLabel.text = #"example text";
return cellView;
}
This fails when I try to assign the result to the titleLabel.text:
- (TableViewCell *)tableView:(tableView *)tableView cellAtIndex:(NSUInteger)index {
TableViewCell *cellView = [[TableViewCell alloc] init];
NSString *result = [_googleSuggestions objectAtIndex:index];
NSLog(#"Result: %#", result);
cellView.titleLabel.text = result;
return cellView;
}
It makes no sense, it's clearly an NSString variable assigned to an object that has no problem with NSString variables like shown in the working examples above.
How do you properly implement async search results?
How do you properly update UI elements from a background thread?