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Question

respondsToSelector send to deallocated object

Answer 1

A:

Zombie is disabled as you use it with Memory Leaks since all Zombies would be signaled as leaks. To run the Zombie tool you can go to the Instrument menu and do File>New and chose the Zombie tool alone, doing so the program will stop if a zombie has received a message and you'll be given a link in a small pop up to that zombie object and its history

rano 2010-08-28 18:51:44

Thanks for the hint! I realized this when reading http://www.corbinstreehouse.com/blog/2007/10/instruments-on-leopard-how-to-debug-those-random-crashes-in-your-cocoa-app/I didn't knew that Instruments is a standalone program and not part of Xcode. Nevertheless I don't understand why they are offering that menu entry, if it couldn't be used.

testing 2010-08-29 09:53:34

Answer 2

A:

Somewhere you're allocating the XMLParser. Let's see that code. You're not auto-releasing it, are you?

Somewhere it's getting released... is it assigned to a property? Let's see that property definition.

Later on the respondsToSelector: method is being invoked, but that could be any method. The point is that your XMLParser got released before you intended.

Graham Perks 2010-08-29 01:53:32

So I edited my question. I'm using alloc, so I don't think I'm autoreleasing it. I don't use the RSS Parser as a property. When it is the right time to release it?

testing 2010-08-29 09:58:47

Looks like your XMLParser class is expecting some async I/O response? If so, it needs to hang around until complete. Therefore you can't release it in loadData. Autoreleasing itself in connectionDidFinishLoading: would be worth trying, if that's when it completes processing. You'd have to do the same in any connection error handling method, too.

Graham Perks 2010-08-29 12:36:41

I didn't looked through the synchronous/asynchronous stuff. So I'm telling you what I use. I use NSURLConnection and NSXMLParser. NSURLConnection is creating asynchronous connections and the NSXMLParser is a SAX Parser. Since I'm starting the parsing in connectionDidFinishLoading: the parsing takes place, when the file was downloaded (the faulty file is a HTML file, where a redirection takes place after 5 seconds). The project is based on this tutorial: http://www.cocoadevblog.com/iphone-tutorial-creating-a-rss-feed-reader.

testing 2010-08-30 08:12:41

Answer 3

A:

In RootViewController.h I have declared the property rssParser:

@class XMLParser;

@interface RootViewController : UITableViewController {
    ...
    XMLParser *rssParser;
}
...
@property (retain, nonatomic) XMLParser *rssParser;

@end

In RootViewController.m I have a method called errorOccurred:

- (void)errorOccurred {
    [rssParser release];
    rssParser = nil;
    if ([activityIndicator isAnimating]) {
        [activityIndicator stopAnimating];
    }
}

In my XMLParser.m file I call the errorOccurred two times:

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
    ...

    if ([_delegate respondsToSelector:@selector(errorOccurred)])
        [_delegate errorOccurred];
    else  
    {   
        [NSException raise:NSInternalInconsistencyException  
                    format:@"Delegate doesn't respond to errorOccurred:"];  
    }
}

To see how _delegate is declared, look at the tutorial http://www.cocoadevblog.com/iphone-tutorial-creating-a-rss-feed-reader. It is an id variable and has a own setter and getter method (you can also declare it as property I think). The second time:

- (void)parser:(NSXMLParser *)parser parseErrorOccurred:(NSError *)parseError {
    ...

    if ([_delegate respondsToSelector:@selector(errorOccurred)])
        [_delegate errorOccurred];
    else  
    {   
        [NSException raise:NSInternalInconsistencyException  
                    format:@"Delegate doesn't respond to errorOccurred:"];  
    }
}

The release of my rssParser variables are like the following:

In loadData in RootViewController.m I never release it. Unfortunately it will crash if I do it in loadData. It is only released if a error occurred (see above) or in the dealloc method. But I think that should work fine as it is declared as property.

- (void)loadData {
    if (newsItems == nil) {
        [activityIndicator startAnimating];  

        self.rssParser = [[XMLParser alloc] init];  
        [rssParser parseRssFeed:@"http://www.wrongurl.com/wrongrss.xml" withDelegate:self];  
    } else {  
        [self.tableView reloadData];  
    }  
}

In XMLParser.m I release it after the parse method:

- (void)connectionDidFinishLoading:(NSURLConnection *)connection {  
   ...

    NSXMLParser *rssParser = [[NSXMLParser alloc] initWithData:responseData];

    [rssParser setDelegate:self];

    [rssParser parse];

    [rssParser release];
    rssParser = nil;
}

Note that the two variable names are the same (rssParser), but they are different. In RootViewController I'm creating an instance of XMLParser, and in XMLParser.m I'm creating an instance of NSXMLParser.

So I think I'll leave it at that, until I'm not experiencing a new error or someone of you explain me why this is bad.

testing 2010-08-30 11:42:23

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