Creating a global variable in swift - swift

Question

I am trying to create a global variable from my view controller (inside the class but outside the functions) as follows:
var modelData: CustomTabBarController.model // THE ERROR IS HERE
This is how that class is defined:
CustomTabBarController.swift:
import UIKit
// This class holds the data for my model.
class ModelData {
var name = "Fred"
var age = 50
}
class CustomTabBarController: UITabBarController {
// Instantiate the one copy of the model data that will be accessed
// by all of the tabs.
var model = ModelData()
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
}
}
However I am getting the following error:
"'model' is not a member type of "CustomTabBarController"
How do I declare it so that I can access model? Thanks.
Update #1
Sorry I forgot to mention this:
I need the model data to be the SAME in every tab of the tabbar. For example if I change the age to 51 in the first tab, the second tabbar should retrieve 51. Which would be the correct method above to use it this way?
Update #2
I am able to create the variable inside a function with dean's suggestion:
func setupModelData()
{
var modelData = (self.tabBarController as! CustomTabBarController).model
}
However this does not work, since I need to access the modelData from other functions. When I attempt to move this line outside of the function as follows:
import UIKit
class FirstViewController: UIViewController, UITableViewDelegate, UITableViewDataSource
{
var modelData = (self.tabBarController as! CustomTabBarController).model
...
I receive the error:
Value of type '(NSObject) -> () -> FirstViewController' has no member 'tabBarController'

Answer 1

I ended up following holex's suggestion of creating a shared class (singleton):
import UIKit
class ModelData: NSObject {
static let shared: ModelData = ModelData()
var name = "Fred"
var age = 50
}
Writing in first view: Set age to 51:
ModelData.shared.age = 51
Reading in second view: Get age of 51
let age = ModelData.shared.age

Answer 2

I'm not sure whether you truly want a global variable (i.e. a single instance of ModelData shared between all your view controllers) or an instance variable which is public, so I'll try to answer both :)
1) global model
This line attempts to get the model property from the CustomerTabBarController class - i.e. if you made multiple tab bar controllers they would all use the same model.
var modelData: CustomTabBarController.model
If this is what you want, then you need to change this line to include the static keyword.
static var model = ModelData()
However, this almost certainly isn't what you're after.
2) shared instance variable
This means that the model is part of each instance of CustomTabBarController. Here, you would need to change the line which is throwing the error to be something like this:
var modelData: myCustomTabBarController.model
Without knowing more about your architecture, I can't help you get hold of your tab bar controller instance, but something like this might work (inside other view controllers):
var modelData = (self.tabBarController as! CustomTabBarController).model

Answer 3

model is an instance variable.
Either create an instance of CustomTabBarController
var modelData = CustomTabBarController().model
Or declare model as class variable
static var model = ModelData()
...
var modelData = CustomTabBarController.model
However to use ModelData as a single global variable with the two members, use a struct rather than a class and declare the members as static.
struct ModelData {
static var name = "Fred"
static var age = 50
}
You can access the name from everywhere for example
let name = ModelData.name
and there is no need to create an extra variable in another class.
An – instance based –  alternative is a singleton
struct ModelData {
static let shared = ModelData()
var name = "Fred"
var age = 50
}
and use it
let name = ModelData.shared.name