Question

I am trying to load JSON from a sever and then display it in a UITableView. The request goes fine however when I try to add the data to the tableview the app crashes when I call then [tableView reloadData] method is called. I have the variable jsonArray reference in the UITableView methods so that the TableView displays the contents of that variable. Is this the best way to do it and what am I doing wrong?

The connection

NSURLConnection *theConnection=[[NSURLConnection alloc] initWithRequest:theRequest delegate:self];

Main HTTP Callback

- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    [connection release];

    NSString *responseString = [[NSString alloc] initWithData:responseData encoding:NSUTF8StringEncoding];
    [responseData release];

    //Declare the parser
    SBJsonParser *parser = [[SBJsonParser alloc] init];

    jsonArray = [parser objectWithString:responseString];

    [tableView reloadData];

    [parser release];
    [responseString release];
}

Error

2011-07-07 14:42:56.923 Viiad[16370:207] -[__NSSet0 objectAtIndex:]: unrecognized selector sent to instance 0x5a4a0b0
2011-07-07 14:42:56.925 Viiad[16370:207] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSSet0 objectAtIndex:]: unrecognized selector sent to instance 0x5a4a0b0'

EDIT

UITableViewMethods

// Customize the appearance of table view cells.
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {

    static NSString *CellIdentifier = @"Cell";

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];

    if (cell == nil) {
        cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease];
    }

    NSArray *results = [[jsonArray valueForKey:@"Rows"] valueForKey:@"name"];

    cell.textLabel.text = (NSString *)[results objectAtIndex:indexPath.row];
    return cell;
}

Answer 1

This message

-[__NSSet0 objectAtIndex:]: unrecognized selector sent to instance 0x5a4a0b0

means that someplace in the code, the objectAtIndex: message was sent to an instance of __NSSet0. To me, that looks like you’re passing around an NSSet where you’re expecting an NSArray.

Set a debugger breakpoint before you call [results objectAtIndex:indexPath.row] and see what results actually contains. My guess is that the JSON parser isn’t returning what you think it is. Objective-C is dynamically typed: just because you say that a variable is an NSArray type doesn’t mean it can’t contain some other object. If a function returns type id, there is no type information for the compiler to check at all.