Swift Passing data from appDelegate to another class

Question

I need to pass a variable from the AppDelegate to another class that I have created to hold global variables of the project and I'm not able to find a way to make it work.

This is the code in the AppDelegate:

func application(application: UIApplication!, didRegisterForRemoteNotificationsWithDeviceToken deviceToken: NSData!) {
    println("Device's token is: \(deviceToken)")

    //Global Variables Class Instance
    let globals:Globals = Globals()

    globals.setDeviceToken("test1") //method1 not working
    globals.deviceToken = "test2"   //method2 not working
}

This is my Globals Class:

public class Globals {
    var deviceToken = String()

    init() {
        //nothing
    }

    func setDeviceToken(s:String){
        deviceToken = s
    }

    func getDeviceToken() -> String {
        return deviceToken
    }
}

If i try to print the value, from other files of the project, I'm not able to get anything, just an empty string.

class ViewController: UIViewController {

    //Global Variables Class Instance
    let globals:Globals = Globals()

    override func viewDidLoad() {
        println(globals.getDeviceToken())  //return empty string
        println(globals.deviceToken)       //return empty string

How much data should be held in the app delegate? NONE! EVER! Don't do it. It isn't what the app delegate is for. — Fogmeister, Nov 03 '14 at 14:38
There is no need to get upset, I'm just a beginner and I'm trying to learn. @Fogmeister — MeV, Nov 06 '14 at 11:05

score 15 · Accepted Answer · answered Nov 03 '14 at 14:38

There are several patterns you can use to achieve what you want

You could access the AppDelegate through the UIApplication:

let delegate = UIApplication.sharedApplication().delegate as AppDelegate
let deviceToken = delegate.deviceToken

Look into singletons. A quick google search for 'Swift singleton' will get you a long way. The first result:

class SingletonB {

        class var sharedInstance : SingletonB {
        struct Static {
            static let instance : SingletonB = SingletonB()
        }
        return Static.instance
    }
}

Then use sharedInstance to instantiate the singleton anywhere and access the same variables.

The first one is quick and dirty, so for more serious projects I would recommend the singleton pattern.

There are probably a million ways to do this, but this should get you started

(More at this link, which explores a few ways to implement singletons: https://github.com/hpique/SwiftSingleton )

Thanks for your reply. I never used singleton and need to read some documentation about it. But the code looks very similar to the one I was using for Globals. @Bob Vork — MeV, Nov 03 '14 at 14:53
As documented in the linked-to article, the above rather convoluted way of creating a singleton is not needed if you're using Swift 1.2 or later. — RenniePet, Mar 03 '17 at 06:08

score 5 · Answer 2 · edited Sep 18 '18 at 12:21

5

I simply solved my problem using NSUserDefaults

in the AppDelegate:

NSUserDefaults.standardUserDefaults().setObject(deviceToken, forKey: "deviceToken")
NSUserDefaults.standardUserDefaults().synchronize()

From other classes:

NSUserDefaults.standardUserDefaults().objectForKey("deviceToken")

Honestly I don't know if this is a good way to do it but it's working

edited Sep 18 '18 at 12:21

Matei Suica

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answered Nov 03 '14 at 14:55

MeV

3,761
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hi! I'd like to know why it is not recommended to use NSUserDefaults ? – Matthew Usdin Aug 17 '15 at 21:06
mattyU you need to ask @Fogmeister up here, cause he commented my question – MeV Aug 18 '15 at 17:09
1

NSUserdefaults takes time to store data, and you can't store any type of data without trouble. NSUserdefaults should only be used to save data between sessions. – Rickard Elimää Apr 09 '18 at 07:29

Swift Passing data from appDelegate to another class

2 Answers2