Why my font size is not scaling dynamically

Question

Created Jul ’25

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Hello everyone, I am having an issue where the attributed text that I have in my UITextView is not scaling dynamically with phone text size, whenever I remove the attributed text logic, it scales fine, however, with it, it stays at a set font size.

struct AutoDetectedClickableDataView: UIViewRepresentable {
    let text: String
    @Binding var height: CGFloat

    func makeUIView(context: Context) -> UITextView {
        let textView = UITextView()
        textView.dataDetectorTypes = [.phoneNumber, .address, .link]
        textView.isEditable = false
        textView.isScrollEnabled = false
        textView.backgroundColor = .clear
        textView.font = UIFont.preferredFont(forTextStyle: .body) /*UIFontMetrics(forTextStyle: .body).scaledFont(for: UIFont.systemFont(ofSize: 16.0)) */
        textView.adjustsFontForContentSizeCategory = true
        textView.textContainer.lineBreakMode = .byWordWrapping
        textView.textContainerInset = .zero
        textView.textContainer.lineFragmentPadding = 0
        textView.translatesAutoresizingMaskIntoConstraints = false
        textView.setContentCompressionResistancePriority(.defaultLow, for: .horizontal)
        textView.setContentHuggingPriority(.defaultHigh, for: .horizontal)
        return textView
    }

    func updateUIView(_ uiView: UITextView, context: Context) {

        let attributed = NSMutableAttributedString(string: text, attributes: [
            .font: UIFont.preferredFont(forTextStyle: .body)
        ])
        
        let detector = try? NSDataDetector(types: NSTextCheckingResult.CheckingType.address.rawValue |
                                           NSTextCheckingResult.CheckingType.link.rawValue |
                                           NSTextCheckingResult.CheckingType.phoneNumber.rawValue)

        detector?.enumerateMatches(in: text, options: [], range: NSRange(location: 0, length: text.utf16.count)) { match, _, _ in
            guard let match = match else { return }
            
            attributed.addAttributes([
                .foregroundColor: UIColor.systemBlue,
                .underlineStyle: NSUnderlineStyle.single.rawValue,
            ], range: match.range)
        }
        
        uiView.attributedText = attributed
//        uiView.text = text
        DispatchQueue.main.async {
            uiView.layoutIfNeeded()
            let fittingSize = CGSize(width: uiView.bounds.width, height: .greatestFiniteMagnitude)
            let size = uiView.sizeThatFits(fittingSize)
            height = size.height
        }
    }
}

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Answer 1

Etresoft OP

Jul ’25

That's an inherent problem with attributed strings. Should they appear as the current appearance or as specified by the attributes? There are valid reasons for either approach.

You are assigning a font attribute both to the text view and the attributed string. If you remove the attribute from the string, then it might work as you want. Sometimes attributed views can make sense of partial attributes where the text colour is defined by the system appearance, the font is specified as a dynamic type on the view, and the style is defined in the attributed string itself.

Alas, no guarantees. In some cases, you have to hack it. Apple provides the UIFontMetrics class so that you can manually scale things along with dynamic type.

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