traitCollectionDidChange strange behavior

问题

override func traitCollectionDidChange(_ previousTraitCollection: UITraitCollection?) {
    super.traitCollectionDidChange(previousTraitCollection)
    if traitCollection.hasDifferentColorAppearance(comparedTo: previousTraitCollection) {
        print("changed")
    }
}

The iOS 13 application just goes to background without changing the mode (light/dark) but the "print" function is called. Is it possible to determine the moment when the mode really changed?

Thank You.

回答1:

I observed this myself as well.
The user interface toggles as soon as you go to the background, however - it immediately toggles back.
I guess you should simple follow the changes and react as needed.
You can find the current interface style by checking traitCollection.userInterfaceStyle.
For instance:
let isDark = traitCollection.userInterfaceStyle == .dark

来源：https://stackoverflow.com/questions/59139757/traitcollectiondidchange-strange-behavior