Swift. How can I deal with null values into json files?

Question

I'm reading json from a URL and, again (I had the same issue with ObjectiveC) the values crash my app. I don't have any problems with Strings and Numbers. I can println(value) but when I assign the value into a UILabel, it crashes.

I use this method to read the JSON:

func jsonFromURL(jsonURL: String) -> Dictionary<String, AnyObject> {
    var jsonNSURL: NSURL = NSURL(string: jsonURL)
    let jsonSource: NSData = NSData(contentsOfURL: jsonNSURL)
    var json = NSJSONSerialization.JSONObjectWithData(jsonSource, options:NSJSONReadingOptions.MutableContainers, error: nil) as Dictionary<String, AnyObject>
    return json
}

...and this code to assign values into a UILabel inside a custom Cell

func tableView(tableView: UITableView!, cellForRowAtIndexPath indexPath: NSIndexPath!) -> UITableViewCell? {

    var regularTextCell:celda = celda(style: UITableViewCellStyle.Default, reuseIdentifier: "cell")
    var cell:celda = NSBundle.mainBundle().loadNibNamed("celda", owner: self, options: nil)[0] as celda

    cell.name.text = myJson["list"]![indexPath.row]!["name"] as String
    cell.id.text = "id: " + String(myJson["list"]![indexPath.row]!["id"] as Int)

    // THIS line crash because some values of adress are <null>
    cell.address.text = myJson["list"]![indexPath.row]!["address"] as String

    return cell

}

You can view an example of the JSON at: https://dl.dropboxusercontent.com/u/787784/example.json

Thanks!

Answer 1

You'll get an exception from syntax like object as String if object is not a String. You can avoid the exception by using object as? String which may result in a nil being assigned into your text.

In your specific case you could use:

cell.address.text = (myJson["list"]![indexPath.row]!["address"] as? String) ?? "default"

where I've replaced your as with as? and exploited the nil-coalescing operator ??.

Answer 2

I found this solution in online Swift tutorial. It's very nice solution how to deal with null value in Swift.

This is the concept:

 let finalVariable = possiblyNilVariable ?? "Definitely Not Nil Variable"

In tutorial example :

  let thumbnailURL = result["artworkUrl60"] as? String ?? ""

Here is the link for tutorial: http://jamesonquave.com/blog/developing-ios-8-apps-using-swift-interaction-with-multiple-views/