dotnet/wpf · error · NotSupportedException

SR.Unsupported_MouseAction (mouseActionToken)

Error message

SR.Unsupported_MouseAction (mouseActionToken)

What it means

MouseActionConverter.ConvertFrom parses a string into a MouseAction; a token that matches none of the known names (LeftClick, RightClick, MiddleClick, WheelClick, LeftDoubleClick, RightDoubleClick, MiddleDoubleClick) throws NotSupportedException with SR.Unsupported_MouseAction. Matching is case-insensitive but the text must equal one of these tokens exactly.

Solutions

  1. Use one of the exact token names: LeftClick, RightClick, MiddleClick, WheelClick, LeftDoubleClick, RightDoubleClick, MiddleDoubleClick (case-insensitive)
  2. Fix typos in XAML, e.g. Gesture="LeftClick" instead of "Click"
  3. Pre-validate the string against the token list and show a friendly message

Example fix

// before
<MouseBinding Gesture="Click" Command="..."/>
// after
<MouseBinding Gesture="LeftClick" Command="..."/>
Defensive patterns

Strategy: validation

Validate before calling

string[] valid = {"LeftClick","RightClick","MiddleClick","WheelClick","LeftDoubleClick","RightDoubleClick","MiddleDoubleClick"};
bool ok = valid.Contains(s, StringComparer.OrdinalIgnoreCase);

Try / catch

try { action = (MouseAction)converter.ConvertFrom(s); } catch (NotSupportedException ex) { /* unknown MouseAction token */ }

Prevention

When it happens

Trigger: Calling ConvertFrom with strings like "Click", "LeftClick2", "DoubleClick", or localized/translated names; also XAML attribute values with typos.

Common situations: XAML MouseBinding Gesture="Click" (missing the Left prefix) or parsing user-supplied shortcut strings that don't match the canonical token names.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/4ded541f49d3642c. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Input/Command/MouseActionConverter.cs:70

        /// <returns>A <see cref="MouseAction"/> representing the <see langword="string"/> specified by <paramref name="source"/>.</returns>
        public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object source)
        {
            if (source is not string mouseAction)
                throw GetConvertFromException(source);

            ReadOnlySpan<char> mouseActionToken = mouseAction.AsSpan().Trim();
            return mouseActionToken switch
            {
                _ when mouseActionToken.IsEmpty => MouseAction.None, // Special casing as produced by "ConvertTo"
                _ when mouseActionToken.Equals("None", StringComparison.OrdinalIgnoreCase) => MouseAction.None,
                _ when mouseActionToken.Equals("LeftClick", StringComparison.OrdinalIgnoreCase) => MouseAction.LeftClick,
                _ when mouseActionToken.Equals("RightClick", StringComparison.OrdinalIgnoreCase) => MouseAction.RightClick,
                _ when mouseActionToken.Equals("MiddleClick", StringComparison.OrdinalIgnoreCase) => MouseAction.MiddleClick,
                _ when mouseActionToken.Equals("WheelClick", StringComparison.OrdinalIgnoreCase) => MouseAction.WheelClick,
                _ when mouseActionToken.Equals("LeftDoubleClick", StringComparison.OrdinalIgnoreCase) => MouseAction.LeftDoubleClick,
                _ when mouseActionToken.Equals("RightDoubleClick", StringComparison.OrdinalIgnoreCase) => MouseAction.RightDoubleClick,
                _ when mouseActionToken.Equals("MiddleDoubleClick", StringComparison.OrdinalIgnoreCase) => MouseAction.MiddleDoubleClick,
                _ => throw new NotSupportedException(SR.Format(SR.Unsupported_MouseAction, mouseActionToken.ToString()))
            };
        }

        /// <summary>
        /// Converts a <paramref name="value"/> of <see cref="MouseAction"/> to its <see langword="string"/> represensation.
        /// </summary>
        /// <param name="context">Serialization Context</param>
        /// <param name="culture">Culture Info</param>
        /// <param name="value">MouseAction value </param>
        /// <param name="destinationType">Type to Convert</param>
        /// <returns>A <see langword="string"/> representing the <see cref="MouseAction"/> specified by <paramref name="value"/>.</returns>
        public override object ConvertTo(ITypeDescriptorContext context, CultureInfo culture, object value, Type destinationType)
        {
            ArgumentNullException.ThrowIfNull(destinationType);

            if (value is null || destinationType != typeof(string))
                throw GetConvertToException(value, destinationType);

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