How do I know when iPhone download is complete?

I create an array using: 

NSURL *url = [NSURL URLWithString:@"http;//www.myadress.myplist.plist"];f

NSArray *tmp = [NSArray arrayWithContentsOfURL:url];

How do I know when the download is complete? 

-[NSArray arrayWithContentsOfURL] is a synchronous method--the thread will block until the download is complete. (For this reason, it's usually a bad idea to use it on the main thread--either use it on a separate thread or use the asynchronous NSURLConnection methods instead).