Crash when loading data?

[Jake]

Hello everyone. I'm noticing a very strange problem when trying to access string values from an NSDictionary. I load the data from a URL and parse the JSON with this code, storing only the 'sets' value as an NSArray of NSDictionaries:

 // Prepare URL request to download data
    NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:urlString]];
    
    // Perform request and get JSON back as a NSData object
    NSData *response = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];
    
    // Get JSON as a NSString from NSData response
    NSString *responseData = [[NSString alloc] initWithData:response encoding:NSUTF8StringEncoding];
    
    NSDictionary *results = [responseData JSONValue];
    
    resultArray = (NSArray *)[results objectForKey:@"sets"];

I then try to populate a UITableView with that data using the following code (downloadManager was the class where the code above is located):

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    return [[downloadManager resultArray] count];
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    // Set up cell
    static NSString *cellIdentifier = @"TableCellIdentifier";
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:cellIdentifier];
    
    // If a cell doesn't exist, create it.
    if (cell == nil) {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:cellIdentifier];
    }
    
    // Set up cell
    if ([[downloadManager resultArray] count] > 0) {
        NSDictionary *rowData = [[downloadManager resultArray] objectAtIndex:[indexPath row]]; // <- always produces a crash, without any log info
        [[cell textLabel] setText:[rowData objectForKey:@"title"]];
    }else{
        NSLog(@"No data returned.");
    }
    
    // Return the cell
    return cell;
}

Maybe I'm missing something obvious, but I simply cannot access the data from the dictionary without the simulator crashing. (Even with NSLog.) Is there something wrong with my code that could be causing this?

[dljeffery]

Turn on zombies. I would guess that the "[responseData JSONValue]" result is autoreleased (should be) and you don't seem to be doing anything to retain your "resultArray".

[Jake]

Originally Posted by dljeffery

Turn on zombies. I would guess that the "[responseData JSONValue]" result is autoreleased (should be) and you don't seem to be doing anything to retain your "resultArray".

I think you may be right. With zombies enabled I'm getting the following error in the console:

*** -[__NSArrayM count]: message sent to deallocated instance 0x5977370

In the DownloadManager.h file, I set the 'resultArray' to 'retain' in the property declaration. Is there something else I need to do to prevent the variable from being released?

[dljeffery]

There absolutely is. You need to use your property properly. Right now you're just setting the variable directly, and bypassing the generated setter. There are tons of posts on the forum about this; I'd suggest reading through some of them.

But in short, use "self.resultArray = ...", not just "resultArray = ...".

[Jake]

Originally Posted by dljeffery

There absolutely is. You need to use your property properly. Right now you're just setting the variable directly, and bypassing the generated setter. There are tons of posts on the forum about this; I'd suggest reading through some of them.

But in short, use "self.resultArray = ...", not just "resultArray = ...".

I completely forgot about the setters used by Obj-C. (I come from a PHP background.) I changed my code to have the DownloadManager return the array to the view controller instead of accessing it directly, and then properly set it to a variable. The UITableView now displays the data properly, without crashing.

Thank you very much for your help! I'll be sure to remember to use the default setters from now on.