I have a ViewController declared as:
@interface DownloadViewController : UIViewController
<
If you're having problems, you could consider using the well regarded ASIHTTPRequest library to manage your download. It takes care of everything for you.
For example, just 2 lines will do it.
ASIHTTPRequest *request = [ASIHTTPRequest requestWithURL:url];
[request setDownloadDestinationPath:fullPathOfWhereToStoreFile];