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iOS Build a Weather App with Swift (Retired) Concurrency Writing Concurrent Networking Code

Posted by Grace Copplestone
Grace Copplestone
3,779 Points

Add a ! to forecastURL

I was having trouble with code as it was written in the tutorial. May be an issue as a result of new release of xcode.

Anyway, if you're having trouble try unwrapping the forecastURL optional (see below).

''' override func viewDidLoad() { super.viewDidLoad()

    let baseURL = NSURL(string: "https://api.forecast.io/forecast/\(apiKey)/")
    let forecastURL = NSURL(string: "37.8267,-122.423", relativeToURL: baseURL)
    let sharedSession = NSURLSession.sharedSession()
    let downloadTask: NSURLSessionDownloadTask = sharedSession.downloadTaskWithURL(forecastURL!, completionHandler: { (location: NSURL!, response: NSURLResponse!, error: NSError!) -> Void in
        println(location)
        println(response)
    })
    downloadTask.resume()
}

'''

Note - You need to state apiKey beforehand

5 Answers

Jason Wayne
Jason Wayne
11,688 Points
Jason Wayne
Jason Wayne
11,688 Points

One thing I notice that is the reason why we needed to add the bang symbol (!) is because the forecastURL created is actually an optional NSURL string. It's different between a regular NSURL, since it can accept having it to be nil. So, when you type out NSURL(string:...............), Xcode will give a suggested list, and beside the NSURL, it is stated that it is an optional NSURL.

Hope that makes sense. =S

Tom Davis
Tom Davis
1,796 Points
Tom Davis
Tom Davis
1,796 Points

This solved my problem as well. They need to update this in the notes.

Brett Dillworth
Brett Dillworth
4,170 Points
Brett Dillworth
Brett Dillworth
4,170 Points

Thanks! I was stuck on that for a while.

gooolgi
gooolgi
2,032 Points
gooolgi
gooolgi
2,032 Points

Just to add, make sure your device is connected to wifi as well!!

My device's connection was dropped during the test and I kept getting 'nil'. After resetting my phone's wifi setting, everything works again.

Theresa Andelfinger
PLUS
Theresa Andelfinger
Courses Plus Student 2,400 Points
Theresa Andelfinger
Theresa Andelfinger
Courses Plus Student 2,400 Points

Hey guys, i have the same problem with the optional String but it doesn't help to add the bang. What could be the problem?

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

    downloadTask.resume()

Thanks!

Greg Melson
Greg Melson
3,037 Points
Greg Melson
Greg Melson
3,037 Points

change this piece in your code : "println(location) println(response) " to "println(response); println(error)"

I think your missing a semi colon

So it will look like this: "let downloadTask: NSURLSessionDownloadTask = sharedSession.downloadTaskWithURL(forcastURL!, completionHandler: { (location: NSURL!, response: NSURLResponse!, error: NSError!) -> Void in println(location) ; println(response) }) downloadTask.resume()"

Hope that helps