Is keeping a reference to an URLSessionTask necessary?

Question

I've reading several examples related to URLSession and URLSessionTask where code snippets were shown and/or the sample project was available to download. Examples were about the quite common scenario of requesting some info to a REST service by using URLSessionDataTask, most of them having classes similar to this:

var defaultSession: URLSession
var dataTask: URLSessionDataTask?

override init() {
   let configuration = URLSessionConfiguration.default
   self.defaultSession = URLSession(configuration: configuration, delegate: nil, delegateQueue: self.operationQueue)

   super.init()
}

func callService(with searchUrl: URL, completion: @escaping (Data?, URLResponse?, Error?) -> Void) {
   dataTask = defaultSession.dataTask(with: searchUrl, completionHandler: completion)
   dataTask?.resume()
}

I find that usually a reference to dataTask is kept but it is not used at any other place out of that func. Which would be the reasons to keep a reference to the dataTask?

You can use the reference to cancel/suspend it later – dan May 14 '18 at 14:52 — dan, May 14 '18 at 14:52

Dávid Pásztor · Answer 1 · 2018-07-09T16:08:27.310

6

There's no need to keep reference to a URLSessionDataTask instance if you simply want to execute the data task once. You can simply do defaultSession.dataTask(with: searchUrl, completionHandler: completion).resume()

However, keeping a reference to a URLSessionDataTask instance can be useful in case you want to suspend or cancel it before it finishes execution.

There also seems to be a typo in your callService method. The withUrl input parameter isn't used anywhere, but there's a reference to searchUrl, which isn't an input parameter, so I suppose you wanted to call the URL input parameter searchUrl.

func callService(with searchUrl: URL, completion: @escaping (Data?, URLResponse?, Error?) -> Void) {
   defaultSession.dataTask(with: searchUrl, completionHandler: completion).resume()
}

edited Jul 09 '18 at 16:08

answered May 14 '18 at 14:51

Dávid Pásztor

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Thanks. Indeed, there is a typo in my code snippet, I just corrected it. – AppsDev May 14 '18 at 15:07
I just noticed something in your answer, I guess you meant "cancel an ongoing dataTask" instead of "cancel it before it executes". – AppsDev Jul 07 '18 at 18:59
@AppsDev yeah that was meant to be "cancel before it finishes execution", so I corrected it – Dávid Pásztor Jul 09 '18 at 16:08

Is keeping a reference to an URLSessionTask necessary?

1 Answers1