Global variable in Appdelegate in swift

I am saving some data to a variable of appdelegate from a viewcontroller & fetching it from another view controller.Below is the code of app delegate
class AppDelegate: UIResponder, UIApplicationDelegate {
var window: UIWindow?
var navigationController: UINavigationController?
var mainDic:NSMutableDictionary?

Code to set the mainDic
func filterResponse(response:NSDictionary){

    var appDelegate=AppDelegate()
    appDelegate.mainDic=response.mutableCopy() as? NSMutableDictionary
}

Code to fetch the dictionary.
let appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
println(appDelegate.mainDic)

The issue is I am getting the output nil.Please make me correct.

This is your error
var appDelegate=AppDelegate() //You create a new instance, not get the exist one

You need to access the exiting AppDelegate
let appDelegate = UIApplication.shared.delegate as! AppDelegate

Swift 4.0
 let appDelegate = UIApplication.shared.delegate as! AppDelegate 
 let aVariable = appDelegate.value

Swift 3.0
let appDelegate = UIApplication.shared.delegate as! AppDelegate
let aVariable = appDelegate.someVariable

Swift 2.0
let appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
let aVariable = appDelegate.someVariable