This is about iOS 17 only. The only way I could hack around and achieve something like this was

• find the actual, real, border, get its real values
• sadly just add a fake on top of that layer once found, perfectly replicating it

so

///True™ iOS look of the border, and you can change the color
class FixedUITextField: UITextField {
    
    var completed: Bool = true {
        didSet {
            fakeLayer.borderColor = completed ? rememberDefaultColor : UIColor.red.cgColor
        }
    }
    
    private var rememberDefaultColor: CGColor? = UIColor.gray.cgColor
    
    private lazy var fakeLayer: CALayer = {
        let v = RepairedCALayer()
        for found in layer.sublayers ?? [] {
            if found.borderWidth > 0 {
                layer.insertSublayer(v, above: found)
                v.backgroundColor = found.backgroundColor
                v.borderColor = found.borderColor
                v.borderWidth = found.borderWidth
                v.cornerRadius = found.cornerRadius
                v.cornerCurve = found.cornerCurve
                print("found and covered")
                rememberDefaultColor = found.borderColor
                return v
            }
        }
        // defaults ICO disaster
        v.backgroundColor = UIColor.systemBackground.cgColor
        v.borderColor = UIColor.blue.cgColor
        v.borderWidth = 1.0 / UIScreen.main.scale
        v.cornerRadius = 4.0
        v.cornerCurve = .circular
        layer.addSublayer(v)
        return v
    }()
    
    override func layoutSubviews() {
        super.layoutSubviews()
        fakeLayer.frame = bounds
    }
}

This is about iOS 17 only. Am I missing something really obvious?

This is about iOS 17 only. Even more issues on this time waste …

• for some reason I couldn’t find _UlTextFieldRoundedRectBackgroundViewNeue which appears to be the culprit. It’s right there in Xcode, click and see it, but I couldn’t find anything named that.

• Bizarre: take my code above, instead of adding the fake layer, just change the color of the found layer. You’d think! I cannot for the life of me figure out where in the view cycle they set it. Any place I changed the color, “they” would change it back! The only way I could make it stick was with a timer, for goodness sake – give it a go.

This is about iOS 17 only. Am I missing something really obvious? – is there a way to change the border color of a UITextField as is?

If you are a new SO user or inexperienced programmer, please read this, thanks: don’t click “duplicate” due to the 100 ancient questions that have nothing to do with the subtlety asked here, thank you in advance.