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iOS Build a Weather App with Swift (Retired) Concurrency Using Our JSON Data

Posted by Conor Quinn
Conor Quinn
3,461 Points

Download task issue with unwrapping optional

Hi, unless I change the dataObject parameter in weather dictionary to an optional xcode gives me an error. However, when I run it like that the console returns "fatal error: unexpectedly found nil while unwrapping an Optional value"

Thanks!

Here is my code:

let downloadTask: NSURLSessionDownloadTask = sharedSession.downloadTaskWithURL(forecastURL!, completionHandler: { (location: NSURL!, response: NSURLResponse!, error: NSError!) -> Void in

            if (error == nil) {
                let dataObject = NSData(contentsOfURL: location)
                let weatherDictionary: NSDictionary = NSJSONSerialization.JSONObjectWithData(dataObject!, options: nil, error: nil) as NSDictionary
                println(weatherDictionary)

            }

        })
Dave Faliskie
Dave Faliskie
17,793 Points
Dave Faliskie
Dave Faliskie
17,793 Points

I'm having the same problem did you find a way to fix it?

1 Answer

Unsubscribed User
Unsubscribed User
11,496 Points
Unsubscribed User
Unsubscribed User
11,496 Points

Hi Conor,

That code looks good to me. The error you're getting suggests that you're not getting any data back from web service. When you use the "!" you're promising the swift compiler that the value you're unwrapping will not be "nil", so when it turns out that it is "nil", you get an error.

The most likely cause is a typo or error in one of the above lines where you're defining the baseURL or forecastURL. Make sure you're using the correct api key and that the map coordinates you're giving it are valid. You can test the URL outside of xcode by just copy-pasting it into your browser. If it's correct, you should get a screen full of weather data back.

Kyle Vogel
Kyle Vogel
2,415 Points
Kyle Vogel
Kyle Vogel
2,415 Points

If we simulate an error with the URL on purpose, how can we fix the bang (!) operator unwrapping issue on forecastURL? How can we check to see if that's valid first?