Need to adjust NSJSONSerialization to iOS10 - swift

Question

After upgrading to iOS10 users started complaining about crashes of my app.
I am testing it with iOS10 on the simulator and indeed the app crashes with a message saying "Could not cast value of type '__NSArrayI' to 'NSMutableArray'". Here's my code, please help:
import Foundation
protocol getAllListsModel: class {
func listsDownloadingComplete(downloadedLists: [ContactsList])
}
class ListsDownloader: NSObject, NSURLSessionDataDelegate{
//properties
weak var delegate: getAllListsModel!
var data : NSMutableData = NSMutableData()
func downloadLists() {
let urlPath: String = "http://..."
let url: NSURL = NSURL(string: urlPath)!
var session: NSURLSession!
let configuration = NSURLSessionConfiguration.ephemeralSessionConfiguration() //defaultSessionConfiguration()
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 {
self.parseJSON()
print("Lists downloaded")
}
}
func parseJSON() {
var jsonResult: NSMutableArray = NSMutableArray()
do{
try jsonResult = NSJSONSerialization.JSONObjectWithData(self.data, options:NSJSONReadingOptions.AllowFragments) as! NSMutableArray
} catch let error as NSError {
print(error)
}
var jsonElement: NSDictionary = NSDictionary()
var downloadedLists: [ContactsList] = []
for i in 0...jsonResult.count-1 {
jsonElement = jsonResult[i] as! NSDictionary
let tempContactsList = ContactsList()
//the following insures none of the JsonElement values are nil through optional binding
let id = jsonElement["id"] as? String
let name = jsonElement["name"] as? String
let pin = jsonElement["pin"] as? String
let lastUpdated = jsonElement["created"] as? String
let listAdminDeviceID = jsonElement["admin"] as? String
tempContactsList.id = id
tempContactsList.name = name
tempContactsList.pin = pin
tempContactsList.lastUpdated = lastUpdated
tempContactsList.listAdmin = listAdminDeviceID
downloadedLists.append(tempContactsList)
}
dispatch_async(dispatch_get_main_queue(), { () -> Void in
self.delegate.listsDownloadingComplete(downloadedLists)
})
}
}

Answer 1

Even in iOS 9, there was no guarantee NSJSONSerialization.JSONObjectWithData(_:options:) would return mutable object or not. You should have specified NSJSONReadingOptions.MutableContainers.
And in your code, you are not modifying jsonResult, which means you have no need to declare it as NSMutableArray. Just replace NSMutableArray to NSArray, and then you have no need to specify NSJSONReadingOptions.MutableContainers.
But as vadian is suggesting, you better use Swift types rather than NSArray or NSDictionary. This code should work both in iOS 9 and 10.
func parseJSON() {
var jsonResult: [[String: AnyObject]] = [] //<- use Swift type
do{
try jsonResult = NSJSONSerialization.JSONObjectWithData(self.data, options: []) as! [[String: AnyObject]] //<- convert to Swift type, no need to specify options
} catch let error as NSError {
print(error)
}
var downloadedLists: [ContactsList] = []
for jsonElement in jsonResult { //<- your for-in usage can be simplified
let tempContactsList = ContactsList()
//the following insures none of the JsonElement values are nil through optional binding
let id = jsonElement["id"] as? String
let name = jsonElement["name"] as? String
let pin = jsonElement["pin"] as? String
let lastUpdated = jsonElement["created"] as? String
let listAdminDeviceID = jsonElement["admin"] as? String
tempContactsList.id = id
tempContactsList.name = name
tempContactsList.pin = pin
tempContactsList.lastUpdated = lastUpdated
tempContactsList.listAdmin = listAdminDeviceID
downloadedLists.append(tempContactsList)
}
dispatch_async(dispatch_get_main_queue(), { () -> Void in
self.delegate.listsDownloadingComplete(downloadedLists)
})
}
Try this and check it on iOS 10 devices.
(The as! conversion would cause some weird crashes when your server is malfunctioning, but that would be another issue, so I keep it there.)