How to use NSURLSessionDataTask in Swift

Question

Can someone help me? I can't find a good example for the completion syntax.

var url : NSURL = NSURL.URLWithString("https://itunes.apple.com/search?term=\(searchTerm)&media=software")
var request: NSURLRequest = NSURLRequest(URL:url)
let config = NSURLSessionConfiguration.defaultSessionConfiguration()
let session = NSURLSession.sessionWithConfiguration(config)

NSURLSessionDataTask(session.dataTaskWithRequest(request, completionHandler: ((NSData!, NSURLResponse!, NSError!) -> Void)?)

score 72 · Accepted Answer · edited Jan 08 '16 at 15:07

72

It's unclear what you're asking, but I noticed that you have a couple of errors in the code:

You should create your session using NSURLSession(configuration: config)
session.dataTaskWithRequest returns a NSURLSessionDataTask, so there's no need to wrap it inside NSURLSessionDataTask() (a.k.a instantiating a new NSURLSessionDataTask object).

The completion handler is a closure and here's how you create that particular clousure:

{(data : NSData!, response : NSURLResponse!, error : NSError!) in

    // your code

}

Here's the updated code:

let url = NSURL(string: "https://itunes.apple.com/search?term=\(searchTerm)&media=software")
let request = NSURLRequest(URL: url)
let config = NSURLSessionConfiguration.defaultSessionConfiguration()
let session = NSURLSession(configuration: config)

let task = session.dataTaskWithRequest(request, completionHandler: {(data, response, error) in

    // notice that I can omit the types of data, response and error

    // your code

});

// do whatever you need with the task e.g. run
task.resume()

edited Jan 08 '16 at 15:07

tobiasdm

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answered Jun 04 '14 at 15:12

akashivskyy

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1

You can accept my answer if it was what you were looking for. :) – akashivskyy Jun 05 '14 at 09:16
is it possible to use this implementation for POST as well? – Wojtek Turowicz Jul 09 '14 at 12:42
how do you println the error message? – Alex Nolasco Jul 17 '14 at 00:48
3

make sure to call task .resume() after the closure. this will fire off the request – Tony Aug 14 '14 at 11:34
I tried this code but I get an syntax error : "'URLWithString' is unavailable: use object construction 'NSURL(string:)'" at the first line starting with "var url" . I am using SDK 8.1. Any hints ? – mcfly soft Feb 14 '15 at 19:54
@user1344545 You should do what the error says. ;) – akashivskyy Feb 14 '15 at 21:24
Ok. Understood. Still learning swift :-) – mcfly soft Feb 15 '15 at 09:14
Latest swift wants me to use `NSURLRequest(URL: url!)`. Other than that, it works perfectly, thanks! – Todd Mar 01 '16 at 13:11
See my update for Swift 3.0 below. – Francis Jervis Sep 29 '16 at 18:18

Bogdan · Answer 2 · 2014-06-04T19:26:07.040

13

If you have problems with completion syntax, you can create function for completion before calling dataTaskWithRequest(..) to make it clearer

func handler (data: NSData!, response: NSURLResponse!, error: NSError!) {
            //handle what you need
        }

session.dataTaskWithRequest(request, completionHandler: handler)

edited Jun 04 '14 at 19:26

answered Jun 04 '14 at 15:15

Bogdan

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This is so much easier thanks – Ryan Heitner Jun 10 '14 at 11:26
1

In your simple example right here you have made the structure of closures clear to me. The fact that you can replace them with a func is very enlightening. – almel Jul 03 '14 at 09:47

score 5 · Answer 3 · answered Jul 08 '14 at 06:03

5

You can also use it simply by :-

let url = "api url"

let nsURL = NSURL

let task = NSURLSession.sharedSession().dataTaskWithURL(nsURL) {
(data, response, error) in
   // your condition on success and failure
}

task.resume()

answered Jul 08 '14 at 06:03

Rachit

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Francis Jervis · Answer 4 · 2016-09-29T18:23:39.803

2

Updated @duemonk's code for Swift 3:

do {
    var request = URLRequest(url: URL(string: "https://www.example.com/api/v1")!, cachePolicy: .useProtocolCachePolicy, timeoutInterval: 10.0)

    let config = URLSessionConfiguration.default
    let session = URLSession(configuration: config)

    let task = session.dataTask(with: request, completionHandler: {(data, response, error) in

         if error != nil {

              print(error!.localizedDescription)

         }

         else {
              print(response)
         }
     })

    task.resume()
}

catch {
// handle the error
}

edited Sep 29 '16 at 18:23

answered Sep 29 '16 at 18:17

Francis Jervis

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5

you haven't added anything about the request, if it is SET or GET – μολὼν.λαβέ Dec 20 '16 at 07:03

score 1 · Answer 5 · answered Nov 26 '18 at 21:08

Swift 4.2

    let url = URL(string: "http://url.com")!
    let request = URLRequest(url: url)
    let config = URLSessionConfiguration.default
    let session = URLSession(configuration: config)

    let task = session.dataTask(with: request, completionHandler: {(data, response, error) in
        print(String(data: data!, encoding: .utf8)!)
    });

    task.resume()

score 0 · Answer 6 · answered Jun 10 '14 at 21:00

0

session.dataTaskWithRequest(request, completionHandler: {(data: NSData!, response: NSURLResponse!, error: NSError!) in 
    //code
)}

Hopefully Xcode will be updated to support auto-complete for these, cause the syntax is kind of tricky, and Swift doesn't appear to support declaring the return type yet when used like this.

answered Jun 10 '14 at 21:00

malhal

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Yea, I've noticed that the auto-complete when using swift is pretty hit and miss. There have been a couple of instances that it stopped working all together and I had to restart Xcode. – DookieMan Jun 11 '14 at 21:37
I noticed that even in the Xcode 6.1 GM the auto-complete of params inside the closure doesn't work. And you cant "Jump to definition" while the syntax is incorrect, making the feature rather useless. – malhal Oct 05 '14 at 15:34

How to use NSURLSessionDataTask in Swift

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