Shared session vs. session with default configuration

Question

What are the differences between the two session objects created in these two different ways:

NSURLSession *session = [NSURLSession sharedSession];

and

NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration defaultSessionConfiguration];
NSURLSession *session = [NSURLSession sessionWithConfiguration:configuration];

Answer 1

As you're using them, they're functionally very similar. But using sharedSession doesn't give you the ability to customize the NSURLSessionConfiguration (e.g. tweak the cache, custom headers, etc.) nor use the delegate-based rendition of NSURLSession. But if you don't need those features, feel free to use sharedSession as it's easier.

Answer 2

NSURLSessionConfiguration

session with basic set of properties that control various policies on a sessionwide basis. These properties are set on a session at the time of its creation and cannot be changed later. If you need to change these policy properties, create a new session with a modified session configuration.

sharedSession

Returns a shared singleton session object.

Please review Apple Documents first as these are the source of very information.