view.traitCollection.horizontalSizeClass returning undefined (0) in viewDidLoad

Question

I\'m using a UITextView inside a UIPageViewController, and I want to determine the font size based on the size class of the device.

The first slide of the page view is l

Answer 1

In my case I needed my view to know about the horizontalSizeClass so accessing the UIScreen traitCollection was tempting but not encouraged, so I had something like this:

override func layoutSubviews() {
    super.layoutSubviews()
    print("\(self.traitCollection.horizontalSizeClass.rawValue)")

    switch self.traitCollection.horizontalSizeClass {
    case .regular, .unspecified:
        fontSize = 28

    case .compact:
        fontSize = 20
    }
}

override func traitCollectionDidChange(_ previousTraitCollection: UITraitCollection?) {
    super.traitCollectionDidChange(previousTraitCollection)
    print("\(self.traitCollection.horizontalSizeClass.rawValue)")

    guard let previousTraitCollection = previousTraitCollection else { return }

    if self.traitCollection.horizontalSizeClass != previousTraitCollection.horizontalSizeClass {
        layoutIfNeeded()
    }
}