Get Firebase Documents as Array

Question

I've created a document which contains an array within Firestore.

I now want to store that array locally within my app

I have create an array manually, But how can I populate it with the data from my Firestore document?

//Manually created Array
var devices = [ "Laptop",
                "Tablet",
                "Smartphone",
                "Smartwatch",
                "Games Console"]

override func viewDidLoad() {
    super.viewDidLoad()
    createDevicePicker()
    createToolbar()
    getPickerData()
}

//Function to pull data from Firestore
func getPickerData() {
    let docRef = firebaseDB.collection("devices").document("types")
    docRef.getDocument { (document, error) in
        if let document = document, document.exists {
            //This will print out the data
            var test = document.data()
            print(test)
        } else {
            print("Document does not exist")
        }
    }
}

This is what my Firestore DB looks like

Answer 1

document.data() comes in as [String: Any].

As long as it's an Array of Strings in your Firestore

let array = document.data()["devices"] as! [String]
print(array) 

UPDATE TO QUESTION

How to append to the already created devices array.

 var devices = [ "Laptop",
                 "Tablet",
                 "Smartphone",
                 "Smartwatch",
                 "Games Console"]

 let array = data["sub_category"] as! [String]
 devices += array
 print(devices)