iOS - calling Webservice and parsing JSON in Swift - ios

Question

I am using NSURLSession to call my own Webservice which returns JSON, works fine with this code:
func getJSONFromDatabase(){
let url = NSURL(string: "http://www.myurl/mysqlapi.php")
let task = NSURLSession.sharedSession().dataTaskWithURL(url!) {(data, response, error) in
self.json = NSString(data: data!, encoding: NSUTF8StringEncoding)
print(self.json)
}
task.resume()
}
However, it seems that this Task is not executed in the right order, because when i run the following function after the "getJSONFromDatabase" function, the "print" statement in the Task is executed after the "print" statement from the "parseJSON" function.
func parseJSON(){
let data = self.json.dataUsingEncoding(NSUTF8StringEncoding, allowLossyConversion: false)
do {
let json = try NSJSONSerialization.JSONObjectWithData(data!, options: []) as! NSArray
for event in json {
let name = event["name"]
let startDate = event["startDate"]
let dateFormatter = NSDateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd"
let date = dateFormatter.dateFromString(startDate as! String)
if date != nil {
self.events.append(Event(name: name as! String, startDate: date!))
}
else {
print("Date is nil")
}
}
for event in self.events {
print(event.name)
}
} catch let error as NSError {
print("Failed to load: \(error.localizedDescription)")
}
}
My goal is to save the JSON Data in an Object Array of "Event", but this doesn't seem to work because when i iterate over my "self.events" array, it is empty.
Another problem is: When i split this 2 things like i posted here (2 functions), the "parseJSON" throws an error:
Failed to load: The data couldn’t be read because it isn’t in the correct format.
However, if i add the content of "parseJSON" into the Task of the "getJSONFromDatabase" function, there is no such error, but the array is still empty

Answer 1

dataTaskWithURL is asynchronous so you your code won't execute from the top down. Use a completion handler to work on the result from the asynchronous call.
func getJSONFromDatabase(success: ((json: String)->())){
let url = NSURL(string: "http://www.myurl/mysqlapi.php")
let task = NSURLSession.sharedSession().dataTaskWithURL(url!) {(data, response, error) in
let json = NSString(data: data!, encoding: NSUTF8StringEncoding)
success(json: json)
}
task.resume()
}
in use
getJSONFromDatabase(success: {json in
//do stuff with json
})