Swift- Use of unresolved identifier

Question

I have the following Swift code where I am sending a POST request to a webserver and receiving a value back. The error that I receive is on the second to last line saying "Use of unresolved identifier"

func download_request() -> String {
    let url:NSURL = NSURL(string: "http://url.com/read.php")!
    let session = NSURLSession.sharedSession()

    let request = NSMutableURLRequest(URL: url)
    request.HTTPMethod = "POST"
    request.cachePolicy = NSURLRequestCachePolicy.ReloadIgnoringCacheData

    let paramString = "data=name"
    request.HTTPBody = paramString.dataUsingEncoding(NSUTF8StringEncoding)

    let task = session.downloadTaskWithRequest(request) {

        (let location, let response, let error) in

        guard let _:NSURL = location, let _:NSURLResponse = response  where error == nil else {
            print("Error")
            return
        }

        let urlContents = try! NSString(contentsOfURL: location!, encoding: NSUTF8StringEncoding)

        guard let _:NSString = urlContents else {
            print("Error")
            return
        }

     }

    task.resume()
    return urlContents
}

How would I fix this error? I think that it means that I cannot use urlContents outside of the let task = session.downloadTaskWithRequest(request) { } but how would I declare the variable so that I can use it outside?

Ike10 · Accepted Answer · 2016-06-14 03:54:07Z

2

Try declaring urlContents outside of the session.downloadTaskWithRequest(request) { } block. Like so:

func download_request() -> String? {
    let url:NSURL = NSURL(string: "http://url.com/read.php")!
    let session = NSURLSession.sharedSession()
    var urlContents: NSString?

    let request = NSMutableURLRequest(URL: url)
    request.HTTPMethod = "POST"
    request.cachePolicy = NSURLRequestCachePolicy.ReloadIgnoringCacheData

    let paramString = "data=name"
    request.HTTPBody = paramString.dataUsingEncoding(NSUTF8StringEncoding)

    let task = session.downloadTaskWithRequest(request) {

        (let location, let response, let error) in

        guard let _:NSURL = location, let _:NSURLResponse = response  where error == nil else {
            print("Error")
            return
        }

        urlContents = try? NSString(contentsOfURL: location!, encoding: NSUTF8StringEncoding)

        guard let _:NSString = urlContents else {
           print("Error")
           return
        }

     }

    task.resume()
    return (urlContents as! String)
}

Then when you need to use urlContents unwrap it with an if let binding

if let contents = download_request() {
    //Use safely unwrapped contents
}

edited Jun 14, 2016 at 3:54

answered Jun 14, 2016 at 3:34

Ike10

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10 Comments

zam Over a year ago

This fixed the error, however, I now get a different error when building and running: fatal error: unexpectedly found nil while unwrapping an Optional value

zam Over a year ago

The code fixed that problem but the if statement that lets me us the unwrapped urlContents is not running (as tested by else statement).

Ike10 Over a year ago

Try checking print(contents) inside the if let statement. If this returns nil, then you may want to check you link as it is probably returning nil for content. Also where did you put the if let statement? @DanielZam

zam Over a year ago

I put the if let statement inside of a button press

Ike10 Over a year ago

What are you trying to download? @DanielZam.

|

Santosh · Accepted Answer · 2016-06-14 03:49:54Z

You could make return type optional like below

func download_request() -> String? {
     var urlContents: String?
     ....
     ....
     let task = session.downloadTaskWithRequest(request) {

        (let location, let response, let error) in
        ...
        ...
        ...
        guard let _:NSURL = location, let _:NSURLResponse = response  where error == nil else {
            print("Error")
            return
        }
       urlContents = try! NSString(contentsOfURL: location!, encoding: NSUTF8StringEncoding) as String
        guard let _:NSString = urlContents else {
            print("Error")
            return
        }
    }
    task.resume()
    return urlContents
}

And call the method like

 if let request = download_request() {
     //do anything with your request
 }

Suggesting you to rename your method properly since you are returning the downloaded data not the request.

And this is not the correct way to get your downloaded data back as a return to the method since the completionHandler will be called once the operation is done so urlContents will be nil. Hence create another method which takes String as input and call it within the completionHandler of downloadTaskWithRequest

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