MaterialDesignInXAML/MaterialDesignInXamlToolkit · info · ArgumentNullException

textBox

Error message

textBox

What it means

TextBoxHintProxy is the private adapter binding a WPF TextBox to SmartHint. Its constructor throws ArgumentNullException(nameof(textBox)) if given a null TextBox. Like the RichTextBox proxy it is a private nested class instantiated only by HintProxyFabric.Get(), which already filters nulls, so the guard is defensive and not reachable through the supported public API.

Source

Thrown at src/MaterialDesignThemes.Wpf/HintProxyFabric.TextBox.cs:24

    {
        private readonly TextBox _textBox;

        public bool IsLoaded => _textBox.IsLoaded;

        public bool IsVisible => _textBox.IsVisible;

        public bool IsEmpty() => string.IsNullOrEmpty(_textBox.Text);

        public bool IsFocused() => _textBox.IsKeyboardFocusWithin;

        public event EventHandler? ContentChanged;
        public event EventHandler? IsVisibleChanged;
        public event EventHandler? Loaded;
        public event EventHandler? FocusedChanged;

        public TextBoxHintProxy(TextBox textBox)
        {
            _textBox = textBox ?? throw new ArgumentNullException(nameof(textBox));
            _textBox.TextChanged += TextBoxTextChanged;
            _textBox.Loaded += TextBoxLoaded;
            _textBox.IsVisibleChanged += TextBoxIsVisibleChanged;
            _textBox.IsKeyboardFocusWithinChanged += TextBoxIsKeyboardFocusedChanged;
        }

        private void TextBoxIsKeyboardFocusedChanged(object sender, DependencyPropertyChangedEventArgs e)
            => FocusedChanged?.Invoke(sender, EventArgs.Empty);

        private void TextBoxIsVisibleChanged(object sender, DependencyPropertyChangedEventArgs e)
            => IsVisibleChanged?.Invoke(sender, EventArgs.Empty);

        private void TextBoxLoaded(object sender, RoutedEventArgs e)
            => Loaded?.Invoke(sender, EventArgs.Empty);

        private void TextBoxTextChanged(object sender, TextChangedEventArgs e)
            => ContentChanged?.Invoke(sender, EventArgs.Empty);

View on GitHub (pinned to 98edec3a0b)

Solutions

1. Use HintProxyFabric.Get(control) instead of the private proxy constructor.
2. When registering a custom builder, have the build delegate return null for unsupported/null controls rather than building a proxy with null.

if (control is null) return null;
var proxy = HintProxyFabric.Get(control);

When it happens

Trigger: Only reachable via reflection over the private constructor, or if a future HintProxyFabric change bypasses its existing null check before casting the control to TextBox.

Common situations: Forking/extending the fabric or using reflection to add hint support to a custom control; ordinary SmartHint usage does not trigger it.

Related errors

• textBox
• canBuild
• content
• session
• session

AI-assisted analysis of MaterialDesignInXAML/MaterialDesignInXamlToolkit@98edec3a0b (2026-08-13). Data as JSON: /api/errors/d045dc3cb71cacdd. Report an issue: GitHub.