Completion Handler Error in Swift

Question

I'm trying to make my own method with completion handler in Swift:

func callURL(url: NSURL, username: String, password: String, completionHandler: (NSData?) -> ()?) {
    let request = NSMutableURLRequest(URL: url)
    let un = username
    let pass = password
    let loginString = NSString(format: "%@:%@", un, pass)
    let loginData: NSData = loginString.dataUsingEncoding(NSUTF8StringEncoding)!
    let base64LoginString = loginData.base64EncodedStringWithOptions(NSDataBase64EncodingOptions(0))
    request.setValue("Basic \(base64LoginString)", forHTTPHeaderField: "Authorization")
    completionHandler(NSURLConnection.sendAsynchronousRequest(request, queue: NSOperationQueue.mainQueue()) {(response, data, error) in
        return data
    })
}

But I get error on completion handler line:

'Void' is not convertible to 'NSData'

Answer 1

You are returning an NSData in a function returning Void (the NSURLConnection callback).

You should call the completionHandler within the NSURLConnection callback as it:

func callURL(url: NSURL, username: String, password: String, completionHandler: ((NSData?) -> Void)?) {
    let request = NSMutableURLRequest(URL: url)
    let un = username
    let pass = password
    let loginString = NSString(format: "%@:%@", un, pass)
    let loginData: NSData = loginString.dataUsingEncoding(NSUTF8StringEncoding)!
    let base64LoginString = loginData.base64EncodedStringWithOptions(NSDataBase64EncodingOptions(0))
    request.setValue("Basic \(base64LoginString)", forHTTPHeaderField: "Authorization")
    NSURLConnection.sendAsynchronousRequest(request, queue: NSOperationQueue.mainQueue()) {
        response, data, error in
        if let completion = completionHandler {
            completion(data)
        }
    }