Exception thrown if no data are received - ios

Question

I am using following Class to receive data from an external database:
import Foundation
protocol HomeModelProtocal: class {
func itemsDownloaded(items: NSArray)
}
class HomeModel: NSObject, NSURLSessionDataDelegate {
//properties
weak var delegate: HomeModelProtocal!
var data : NSMutableData = NSMutableData()
var mi_movil: String = ""
let misDatos:NSUserDefaults = NSUserDefaults.standardUserDefaults()
var urlPath: String = "http:...hidden here.."
let parametros = "?id="
func downloadItems() {
mi_movil = misDatos.stringForKey("ID_IPHONE")!
print ("mi_movil en HOMEMODEL:",mi_movil)
urlPath = urlPath + parametros + mi_movil
let url: NSURL = NSURL(string: urlPath)!
var session: NSURLSession!
let configuration = NSURLSessionConfiguration.defaultSessionConfiguration()
print ("LA URL ES: ",url)
session = NSURLSession(configuration: configuration, delegate: self, delegateQueue: nil)
let task = session.dataTaskWithURL(url)
task.resume()
}
func URLSession(session: NSURLSession, dataTask: NSURLSessionDataTask, didReceiveData data: NSData) {
self.data.appendData(data);
}
func URLSession(session: NSURLSession, task: NSURLSessionTask, didCompleteWithError error: NSError?) {
if error != nil {
print("Failed to download data")
}else {
print("Data downloaded")
self.parseJSON()
}
}
func parseJSON() {
var jsonResult: NSMutableArray = NSMutableArray()
do{
jsonResult = try NSJSONSerialization.JSONObjectWithData(self.data, options:NSJSONReadingOptions.AllowFragments) as! NSMutableArray
} catch let error as NSError {
print(error)
}
var jsonElement: NSDictionary = NSDictionary()
let locations: NSMutableArray = NSMutableArray()
for(var i = 0; i < jsonResult.count; i++)
{
jsonElement = jsonResult[i] as! NSDictionary
print (jsonElement)
let location = MiAutoModel()
//the following insures none of the JsonElement values are nil through optional binding
if let id_mis_autos = jsonElement["id_mis_autos"] as? String,
let modelo = jsonElement["modelo"] as? String,
let ano = jsonElement["ano"] as? String,
let id_movil = jsonElement["id_movil"] as? String
{
location.id_mis_autos = id_mis_autos
location.modelo = modelo
location.ano = ano
location.id_movil = id_movil
}
locations.addObject(location)
}
dispatch_async(dispatch_get_main_queue(), { () -> Void in
self.delegate.itemsDownloaded(locations)
})
}
}
If there are received data, it works fine but if there are no data an exception is thrown:
Could not cast value of type '__NSArray0' (0x1a0dd2978) to 'NSMutableArray' (0x1a0dd3490)
What should I change to detect if there are no data to avoid the exception?

Answer 1

Since you don't seem to be modifying jsonResult anywhere, the obvious choice is to make it an NSArray instead of an NSMutableArray, and change the downcasting to match that.

Answer 2

I'm not sure why you're using NSDictionary and NSMutableArray but this is how I would do it:
for result in jsonResult {
guard let jsonElement = result as? [String:AnyObject] else { return }
let locations: [MiAutoModel] = []
let location = MiAutoModel()
//the following insures none of the JsonElement values are nil through optional binding
let id_mis_autos = jsonElement["id_mis_autos"] as? String ?? ""
let modelo = jsonElement["modelo"] as? String ?? ""
let ano = jsonElement["ano"] as? String ?? ""
let id_movil = jsonElement["id_movil"] as? String ?? ""
location.id_mis_autos = id_mis_autos
location.modelo = modelo
location.ano = ano
location.id_movil = id_movil
locations.append(location)
}
You might have to change some of the code depending on your situation.