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.

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
• All action arguments must be provided if any are provided.
• childDependencyObject
• comboBox

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

Appendix: 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)