NSURLSession delegates not called

Question

In the following code, the file downloads just fine. However none of the delegate methods seem to be called as I receive no output whatsoever. the progressView is not update

Answer 1

Interestingly, Apple specifically explains this behavior in their NSURLSessionDataDelegate (but neither in the base delegate NSURLSessionTaskDelegate nor in NSURLSessionDownloadDelegate)

NOTE

An NSURLSession object need not have a delegate. If no delegate is assigned, when you create tasks in that session, you must provide a completion handler block to obtain the data.

Completion handler block are primarily intended as an alternative to using a custom delegate. If you create a task using a method that takes a completion handler block, the delegate methods for response and data delivery are not called.