Get JSON data function - Address noch reachable - NSURLErrorDomain error -1002 - json

Question

I have a function to retrieve JSON data from an certain ip address.
if the ip is not reachable, xcode gives me following error at
var jsonResult = NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions.MutableContainers, error: &err) as NSDictionary
The operation couldn’t be completed. (NSURLErrorDomain error -1002.) fatal error: unexpectedly found nil while unwrapping an Optional value
How can I check, if jsonResult is valid or if ip-address is valid?
func getJsonData() {
let urlAsString = NSUserDefaults.standardUserDefaults().objectForKey("ipAddress") as String
let url: NSURL = NSURL(string: urlAsString)!
let urlSession = NSURLSession.sharedSession()
let jsonQuery = urlSession.dataTaskWithURL(url, completionHandler: { data, response, error -> Void in
if (error != nil) {
println(error.localizedDescription)
}
var err: NSError?
var jsonResult = NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions.MutableContainers, error: &err) as NSDictionary
if (err != nil) {
println("JSON Error \(err!.localizedDescription)")
}
//Display Data
dispatch_async(dispatch_get_main_queue(), {
self.label.text = String(format: "%.3f", (jsonResult["pwr"] as Float!)/1000)
})
})
jsonQuery.resume()
}
Thanks!

Answer 1

if (error != nil) {
println(error.localizedDescription)
}
It's not enough to print an error to debugger console. The error must be handled. Ask yourself - what do you want to do if there is no internet connection? Do you want to display an error to the user? Try to send the request again?
The basic fact is that if there was an error, you cannot continue and parse the data. The data is not there, it was not loaded. If you try to parse the data (which is nil), your app will crash.
if (error != nil) {
//XXX: display error to the user, e.g. using an alert
return; //return immediately, don't proceed to parsing.
}

Answer 2

Create a method like below to check valid url.
func validateUrl (stringURL : NSString) -> Bool {
var urlRegEx = "((https|http)://)((\\w|-)+)(([.]|[/])((\\w|-)+))+"
let predicate = NSPredicate(format:"SELF MATCHES %#", argumentArray:[urlRegEx])
var urlTest = NSPredicate.predicateWithSubstitutionVariables(predicate)
return predicate.evaluateWithObject(stringURL)
}
And then update your method. Add a line to call validate url method.
func getJsonData() {
let urlAsString = NSUserDefaults.standardUserDefaults().objectForKey("ipAddress") as String
var isValidURL = validateUrl(urlAsString)
if (!isValidURL) {
// Return from here. URL is invalid
return
}
let url: NSURL = NSURL(string: urlAsString)!
let urlSession = NSURLSession.sharedSession()
let jsonQuery = urlSession.dataTaskWithURL(url, completionHandler: { data, response, error -> Void in
if (error != nil) {
println(error.localizedDescription)
}
var err: NSError?
var jsonResult = NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions.MutableContainers, error: &err) as NSDictionary
if (err != nil) {
println("JSON Error \(err!.localizedDescription)")
}
//Display Data
dispatch_async(dispatch_get_main_queue(), {
self.label.text = String(format: "%.3f", (jsonResult["pwr"] as Float!)/1000)
})
})
jsonQuery.resume()
}