dotnet/wpf · error · ArgumentException

SR.DocumentViewerArgumentMustBePercentage

Error message

SR.DocumentViewerArgumentMustBePercentage

What it means

The FitToWidth (zoom percentage) command handler converts its parameter back to a double using the viewer's ZoomPercentageConverter; if the converter returns DependencyProperty.UnsetValue the argument is not a valid percentage and ArgumentException (SR.DocumentViewerArgumentMustBePercentage) is thrown naming data.

Solutions

1. Pass a valid percentage string (e.g. "75") or double as the command parameter
2. Verify ZoomPercentageConverter (custom ones included) accepts the formats your UI produces
3. Parse/normalize the zoom input in the view model before invoking the command

Example fix

// before
zoomButton.CommandParameter = string.Format("{0} %", zoom);
// after
zoomButton.CommandParameter = zoom.ToString(CultureInfo.InvariantCulture);

var conv = new ZoomPercentageConverter();
bool ok = conv.ConvertBack(data, typeof(double), null, CultureInfo.InvariantCulture) != DependencyProperty.UnsetValue;

try { viewer.FitToWidthCommand.Execute(data); }
catch (ArgumentException) { /* data is not a valid percentage */ }

When it happens

Trigger: Executing FitToWidthCommand with a parameter the ZoomPercentageConverter cannot parse (e.g. "abc", "150%%", unsupported type); replacing the default ZoomPercentageConverter with one that rejects the input.

Common situations: Toolbar zoom combo boxes emitting formatted strings like "75 %" that the converter does not accept; custom converters returning UnsetValue for localized input.

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

• SR.DocumentViewerArgumentMustBeInteger
• ArgumentOutOfRangeException (timeout was Duration.Automatic)
• Cannot have empty collection of DocumentPageView objects.
• Collection_BadRank
• Collection_CopyTo_ArrayCannotBeMultidimensional

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/17120dd7e86ea39e. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Controls/DocumentViewer.cs:1960

            // Check that args is valid
            ArgumentNullException.ThrowIfNull(data);

            // If a ZoomConverter doesn't exist, create one.
            if (dv._zoomPercentageConverter == null)
            {
                dv._zoomPercentageConverter = new ZoomPercentageConverter();
            }

            // Use ZoomConverter to convert argument to zoom value.
            // We use InvariantCulture because the Command arguments are typically
            // defined in XAML or code, which is culture invariant.
            object zoomValue = dv._zoomPercentageConverter.ConvertBack(data, typeof(double),
                null, CultureInfo.InvariantCulture);

            // Argument wasn't a valid percent, throw an exception.
            if (zoomValue == DependencyProperty.UnsetValue)
            {
                throw new ArgumentException(SR.DocumentViewerArgumentMustBePercentage, nameof(data));
            }
            dv.Zoom = (double)zoomValue;
        }

        #endregion Commands

        /// <summary>
        /// Register our properties' metadata so that our DependencyProperties function.
        /// </summary>
        private static void RegisterMetadata()
        {
            DefaultStyleKeyProperty.OverrideMetadata(typeof(DocumentViewer), new FrameworkPropertyMetadata(typeof(DocumentViewer)));
            _dType = DependencyObjectType.FromSystemTypeInternal(typeof(DocumentViewer));
        }

        /// <summary>
        /// Initializes our DocumentScrollInfo.
        /// </summary>

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