Initialization of immutable value 'dataTask'

Question

I'm not getting any errors, but I am getting the following issue (the yellow triangle in the gutter): "Initialization of immutable value 'dataTask' was never used; consider replacing with assignment to '_' or removing it"

Here is my code:

class NetworkOperation {

    lazy var config: NSURLSessionConfiguration = NSURLSessionConfiguration.defaultSessionConfiguration()
    lazy var session: NSURLSession = NSURLSession(configuration: self.config)
    let queryURL: NSURL

    typealias JSONDictionaryCompletion = ([String: AnyObject]?) -> Void

    init(url: NSURL) {
        self.queryURL = url
    }

    func downloadJSONFromURL(completion: JSONDictionaryCompletion) {

        let request: NSURLRequest = NSURLRequest(URL: queryURL)
        let dataTask = session.dataTaskWithRequest(request) {
            (let data, let response, let error) in

            // 1. Check HTTP response for successful GET request

            if let httpResponse = response as? NSHTTPURLResponse {

                switch(httpResponse.statusCode) {
                case 200:
                    // 2. Create JSON object with data
                    do {
                        let jsonDictionary = try NSJSONSerialization.JSONObjectWithData(data!, options: []) as! [String: AnyObject]
                        completion(jsonDictionary)
                    } catch let error {
                        print("JSON Serialization failed. Error: \(error)")
                    }
                default:
                    print("GET request not successful. HTTP status code: \(httpResponse.statusCode)")
                }

            } else {
                print("Error: Not a valid HTTP response")
            }
        }
    }
}

So what's my problem?

Answer 1 · 2016-03-21T04:37:15Z

March 21, 2016 4:37am

The problem is that you created the dataTask constant, but you never use it at all. To fix the warning (and also actually download data), you need to tell the task to start, using the resume method, like this:

let dataTask = session.dataTaskWithRequest(request) { (let data, let response, let error) in
    // All your handling code here omitted for brevity
}
// Right after you create the task, you need to start it
dataTask.resume()

Answer 2 · 2016-03-21T07:08:39Z

March 21, 2016 7:08am

Glad you posted this!

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Brad Forsyth

Brad Forsyth

Initialization of immutable value 'dataTask'

2 Answers

Michael Hulet

Michael Hulet

Brad Forsyth

Brad Forsyth

Atif Naqvi

Atif Naqvi