NSURLConnection didFailWithError not called?

Why, when an image does not exist at a specified URL, does didFailWithError not get calle开发者_如何学Pythond? For example:

NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:@"http://www.google.com/images/someImageIknowDoesntExist.jpg"] 
                     cachePolicy:NSURLRequestReturnCacheDataElseLoad
                             timeoutInterval:10.0];

        urlConnection = [[NSURLConnection alloc] initWithRequest:request delegate:self];

Does not trigger didFailWithError. How can I get notified that there is no image at the url I try to connect to?

The status code in the response will be 404 when you get the connection:didReceieveResponse: method. The error method only gets called if there was an actually error fetching the URL (like the network went down, or the host doesn't exist, etc).