Question

I’m running into a problem that I’m not sure how to solve. Let me just give some relevant code.

FrontpageViewController (viewDidLoad)

NewsFetcher *newsFetcher = [[NewsFetcher alloc] initWithURL:url];
newsFetcher.delegate = self;
[newsFetcher loadData];

NewsFetcher.h

@property (nonatomic, unsafe_unretained) id <NewsFetcherDelegate> delegate;

I’m using unsafe_unretained because I want my app to work with iOS 4 as well, while still using ARC for convenience.

NewsFetcher.m

- (id)initWithURL:(NSURL *)url {

    self = [super init];

    if (self) {

        self.url = url;
        self.receivedData = [[NSData alloc] init];
    }

    return self;
}

- (void)loadData {

    NSLog(@"%@", self.delegate); // FrontpageViewController, as expected

    NSURLRequest *request = [NSURLRequest requestWithURL:self.url 
                                             cachePolicy:NSURLRequestReloadIgnoringCacheData 
                                         timeoutInterval:15];

    if (self.connectionInProgress)
        [self.connectionInProgress cancel];

    self.connectionInProgress = [[NSURLConnection alloc] initWithRequest:request
                                                                delegate:self
                                                        startImmediately:YES];
}

This all works fine. NewsFetcher conforms to the NSURLConnectionDelegate protocol, so the next method that’s being called is connection:didReceiveData:. However, when I do another NSLog(@"%@", self.delegate) within that method, I get varied results (EXEC_BAD_ACCESS, NSCFDictionary, etc.). I think this means that my delegate property points to a released object, which is weird because it’s supposed to be the view controller that’s still on screen (and therefore couldn’t have been released, right?).

How is my delegate available in one method, but not anymore in the next method? Does it have to do with the unsafe_unretained?

Answer 1

Delegate objects are not retained (by convention) by callers. The expectation is that the caller who set it on your object will retain it. Recommend you use the Instruments tool with zombies (and then with leaks) to see what’s going on.