Question

I have an iPhone app, where I’m displaying a tableview, that’s loaded from an RSS feed. When the view is loaded, I call this method to run in a new NSThread:

- (void)start:(NSURL*)url {
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    NSXMLParser *XMLParser = [[[NSXMLParser alloc] initWithContentsOfURL:url] autorelease];
    [XMLParser setDelegate:self];

    if (items) {
        [items release];
    }
    items = [[NSMutableArray alloc] init];

    [self startParsing:XMLParser];

    [pool drain];
}

It’s working fine, but if the user leaves the view while it’s downloading or parsing the xml, I want the thread to stop running, but how would I stop it from running without leaking memory? Also, if it’s running the -initWithContentsOfURL: method while I want it to stop, how would I stop that method?

Answer 1

If you anticipate needing to control connections (i.e. stopping a connection if the user cancels or navigates away) you should probably use the asynchronous NSURLConnection API to load your data before parsing the XML. In addition to giving you the ability to close connections as needed, you’ll also be able to better respond to network errors.

As NSD pointed out, you should probably implement some sort of cancel method on the class that’s driving your XML parsing thread – then just use performSelector:onThread:withObject:waitUntilDone: (or similar) from your main thread when the user cancels the download or navigates away.