Update UI when toggle between darkmode and lightmode then enter foreground

Question

I have a login screen which look like this:

Basically, i want to setup so that after the following actions: when in this login screen -> enter background -> toggle darkmode or lightmode in settings -> enter foreground ,the dropShadowView and its element are changed accordingly. Here down below is my code:

in viewDidLoad():

override func viewDidLoad() {
        super.viewDidLoad()
        setupForDarkmode()
        NotificationCenter.default.addObserver(self, selector: #selector(willEnterForeground), name: UIApplication.willEnterForegroundNotification, object: nil)
    }

And function:

@objc func willEnterForeground() {
        setupForDarkmode()
    }

    private func setupForDarkmode() {
        if #available(iOS 13.0, *) {
            overrideUserInterfaceStyle = .unspecified
            if traitCollection.userInterfaceStyle == .dark {
                dropShadowView.backgroundColor = .black
                userNameTextField.backgroundColor = .black
                userNameTextField.textColor = .white
                passwordTextField.backgroundColor = .black
                passwordTextField.textColor = .white
            } else {
                dropShadowView.backgroundColor = .white
                userNameTextField.backgroundColor = .gray
                userNameTextField.textColor = .blue
                passwordTextField.backgroundColor = .gray
                passwordTextField.textColor = .blue
            }
        }
    }

screen's background was already set as system's background color.

However these above code wasn't worked as i expected. The first time it enter foreground right after the change in setting, the dropShadowView and its element keep its appearance until the second time.

After debug a while, i found that right after the change in settings (lightmode -> darkmode for exp), at line if traitCollection.userInterfaceStyle == .dark {, it wasn't recognized current userInterfaceStyle at first (unlike system's background color).

My application's target is lower than iOS 11 so i also have some prolem using colorset.

The question is is there and posible way to update the UI for darkmode programmatically when enter foreground?

Thanks in advance.

Just for debugging change your `setupForDarkMode()` to `DispatchQueue.main.asyncAfter(deadline: .now()+2.0) { setupForDarkmode() }` inside `willEnterForeground()` and see if it works — Keshu R., Feb 21 '20 at 07:37
If you use dynamic colours then the UI will update automatically. See https://stackoverflow.com/questions/56487679/how-do-i-easily-support-light-and-dark-mode-with-a-custom-color-used-in-my-app and the WWDC 2019 session on adopting dark mode — Paulw11, Feb 21 '20 at 08:17

score 0 · Accepted Answer · answered Feb 24 '20 at 03:38

The problem is solved. I used custom color and UI was automatically update: How do I easily support light and dark mode with a custom color used in my app?

It should look like this:

extension UIColor {
    static var dropShadowViewBackground: UIColor {
        if #available(iOS 13.0, *) {
            return UIColor { (traits) -> UIColor in
                // Return one of two colors depending on light or dark mode
                return traits.userInterfaceStyle == .dark ? .black : .white
            }
        } else {
            // Same old color used for iOS 12 and earlier
            return .white
        }
    }
}

This work perfectly!

Update UI when toggle between darkmode and lightmode then enter foreground

1 Answers1