Execute a method when a variable value changes in Swift

Question

I need to execute a function when a variable value changes.

I have a singleton class containing a shared variable called labelChange. Values of this va

Answer 1

You can simply use a property observer for the variable, labelChange, and call the function that you want to call inside didSet (or willSet if you want to call it before it has been set):

class SharingManager {
    var labelChange: String = Model().callElements() {
        didSet {
            updateLabel()
        }
    }
    static let sharedInstance = SharingManager()
}

This is explained in Property Observers.

I'm not sure why this didn't work when you tried it, but if you are having trouble because the function you are trying to call (updateLabel) is in a different class, you could add a variable in the SharingManager class to store the function to call when didSet has been called, which you would set to updateLabel in this case.

Edited:

So if you want to edit a label from the ViewController, you would want to have that updateLabel() function in the ViewController class to update the label, but store that function in the singleton class so it can know which function to call:

class SharingManager {
    static let sharedInstance = SharingManager()
    var updateLabel: (() -> Void)?
    var labelChange: String = Model().callElements() {
        didSet {
            updateLabel?()
        }
    }
}

and then set it in whichever class that you have the function that you want to be called, like (assuming updateLabel is the function that you want to call):

SharingManager.sharedInstance.updateLabel = updateLabel

Of course, you will want to make sure that the view controller that is responsible for that function still exists, so the singleton class can call the function.

If you need to call different functions depending on which view controller is visible, you might want to consider Key-Value Observing to get notifications whenever the value for certain variables change.

Also, you never want to initialize a view controller like that and then immediately set the IBOutlets of the view controller, since IBOutlets don't get initialized until the its view actually get loaded. You need to use an existing view controller object in some way.

Hope this helps.