Detecting Change in iOS Dark Mode

Question

I've found a couple questions on here related to the issue I'm having but since I'm fairly new to iOS development I'm not sure how/where people are implementing their solutions. Since I am also new to StackOverflow I cannot comment on their posts so any help would be greatly appreciated.

Detecting iOS Dark Mode Change

How to detect Light\Dark mode change in iOS 13?

I have a collectionView that when I change to and from Dark Mode, the cell borderColor is changing to what looks like black instead of the color it should be based on the systemGray color that I have assigned to it.

In the answers I linked above people suggested using layoutSubviews() and/or traitCollectionDidChange() but I'm not exactly sure where to implement those functions. I can't seem to find the functions in the definitions of UIViewController or UICollectionView.

When I reload the views using reloadData(), the colors change to what they should be but I would like to know when/where the functions layoutSubviews() and/or traitCollectionDidChange() are being called.

It's really difficult to help you fix your code when you don't show your code. Please [edit] your question and include, as text, relevant code that produces your issue. — rmaddy, Sep 28 '19 at 18:13

Anthony · Accepted Answer · 2019-10-21T00:04:07.117

If you'd like to understand how to implement dark mode in iOS 13 I would suggest you watch this wwdc video. However, if you just want a quick understanding of when the methods are called, here is a summary:

layoutSubviews(): The layoutSubviews method is for UIView subclasses. You can override this in your own UIView subclasses like so:

class CustomCollectionView: UICollectionView {
    override func layoutSubviews() {
        super.layoutSubviews()
        // your implementation here
    }
}

traitCollectionDidChange(): The traitCollectionDidChange method can be overrided for UIViewController subclasses. You can override this in your own UIViewController subclasses like so:

class CustomViewController: UIViewController {
    override func traitCollectionDidChange(_ previousTraitCollection: UITraitCollection?) {
        super.traitCollectionDidChange(previousTraitCollection)
        // your implementation here.
    }
}

If you want to specifically know when the theme has changed then your implementation of traitCollectionDidChange would look something like:

public override func traitCollectionDidChange(_ previousTraitCollection: UITraitCollection?) {
    super.traitCollectionDidChange(previousTraitCollection)

    if #available(iOS 13, *), traitCollection.hasDifferentColorAppearance(comparedTo: previousTraitCollection) {
        // handle theme change here.
    }
}

Detecting Change in iOS Dark Mode

1 Answers1