Function to read web via JSON - ios

Question

I am getting this error while trying to write a function which returns an NSDictionary after reading data using JSON:
 Cannot convert the expression's type NSDictionary? to type Void
func readJsonData() -> NSDictionary{
let urlPath = "http://www.telize.com/geoip"
let url = NSURL(string: urlPath)
let session = NSURLSession.sharedSession()
let task = NSURLSession.sharedSession().dataTaskWithURL(url!, completionHandler:{(data , response, error) -> Void in
if (error != nil){
println(error)
}else{
let jsonresult = NSJSONSerialization.JSONObjectWithData(data, options: .MutableContainers, error: nil) as? NSDictionary
return jsonresult
}
})
task.resume()
}

Answer 1

Your completionHandler has a return type of Void but you are returning jsonresult which is of type NSDictionary.
You should remove the line:
return jsonresult
As you should not return a value to a completion handler.
If you want to set a variable in your class on the completion, you can execute a thread on the main queue and set the variable equal to jsonresult:
let task = NSURLSession.sharedSession().dataTaskWithURL(url!, completionHandler:{(data , response, error) -> Void in
if (error != nil){
println(error)
}else{
let jsonresult = NSJSONSerialization.JSONObjectWithData(data, options: .MutableContainers, error: nil) as? NSDictionary
dispatch_async(dispatch_get_main_queue(), {
self.jsonData = jsonresult
//Update GUI, etc.
})
}
})

Answer 2

You'll need to learn how an asynchronous call works. Your function readJsonData cannot work that way.
You call dataTaskWithURL. The call returns immediately, without any result. That's why readJsonData cannot return a dictionary. However, the data that dataTaskWithURL downloads arrives a long time later (100s of milliseconds, or seconds, or maybe a minute). When the data arrives, your callback function is called. The callback cannot return anything because its call has long since returned. The callback must deliver the data to whoever wants it.