Swift 4 - setNeedsDisplay and layoutIfNeeded not redrawing UILabel on self.UIView

Basically, I have a custom UILabel subclass that sets the label colors based on a variable.

class MyLabel: UILabel {
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        textColor = GlobalVars.mainTextColor
    }
}

On my view controller I have a button that sets a white background and sets the text color variable to black:

@IBAction func btnWhite(_ sender: UIButton) {
        GlobalVars.mainTextColor = UIColor.black
        GlobalVars.bgColor = UIColor.white
        self.view.backgroundColor = UIColor.white
        self.view.setNeedsDisplay()
        self.view.layoutIfNeeded()
        DispatchQueue.main.async { [weak self] in
            self?.view.setNeedsLayout()
            self?.view.layoutIfNeeded()
        }
    }

Once this is clicked and the variables updated, I want the ViewController to redraw the labels, which would update their text colors. This work fine if I pop the VC and come back, but I want the display to update when the buttons is clicked. I have a bunch of labels on the view and thy are all set to myLabel class. I do not want to have to manually code changes to every label on the screen, I just want to redraw it. The UIView is not a custom class, just the default UIView that comes with a View Controller. This should be occurring on the main thread already, but I have tried adding the dispatch.main.async just in case. I expect it would not need both in the end. Image of my view controller layout here

When I click the button, the background changes to white, but the label text colors do not update, I believe that is because it is not redrawing them. There is a second button btnBlack, that toggles it the exact opposite for a light/dark mode effect.

Thoughts?

Solution

Whenever GlobalVars.mainTextColor or GlobalVars.bgColor values change, you have to set the colors of all your labels again.

One option is to use Notifications. You can post a notification on didSet of your global variables and catch the notification in your MyLabel class and update the colors.

class GlobalVars {
    static let onChangeColorNotification = "onChangeColorNotification"
    static var mainTextColor:UIColor? {
        didSet {
            NotificationCenter.default.post(Notification.init(name: Notification.Name(rawValue: onChangeColorNotification)))
        }
    }
}

And in your MyLabel class

class MyLabel: UILabel {
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        onChangeGlogabColor()
        NotificationCenter.default.addObserver(self, selector: #selector(onChangeGlogabColor), name: NSNotification.Name(rawValue: GlobalVars.onChangeColorNotification), object: nil)
    }
    @objc func onChangeGlogabColor() {
        textColor = GlobalVars.mainTextColor
    }
}

You can do the same with all your custom classes like MyButton or MyView, catch the notification and update the colors.

And you don't have to call setNeedsDisplay() or layoutIfNeeded().

@IBAction func btnWhite(_ sender: UIButton) {
    GlobalVars.mainTextColor = UIColor.black
    GlobalVars.bgColor = UIColor.white
    self.view.backgroundColor = UIColor.white        
}