dotnet/wpf · error · NotSupportedException

Converter_ConvertToNotSupported

Error message

Converter_ConvertToNotSupported

What it means

ImageSourceConverter.ConvertTo throws NotSupportedException with 'Converter_ConvertToNotSupported' when the ImageSource instance cannot be serialized to a string (CanSerializeToString() returns false). Only certain ImageSources (e.g. those backed by a resolvable URI) support string conversion.

Solutions

  1. Set the image's UriSource so it can serialize to a pack URI string
  2. Avoid serializing non-URI-backed images; assign the image via a resource URI instead
  3. Handle CanSerializeToString()==false by skipping serialization or storing a different representation

Example fix

// before
var bmp = new BitmapImage();
bmp.BeginInit();
bmp.StreamSource = File.OpenRead("img.png"); // no UriSource
bmp.EndInit();
serializer.Serialize(writer, bmp); // throws
// after
var bmp = new BitmapImage(new Uri("pack://application:,,,/img.png"));
serializer.Serialize(writer, bmp);
Defensive patterns

Strategy: fallback

Validate before calling

if (imageSource is ImageSource src && !src.CanSerializeToString())
    throw new NotSupportedException("This ImageSource cannot be serialized to a string; assign a UriSource instead.");

Type guard

bool CanSerializeImage(ImageSource src) => src?.CanSerializeToString() == true;

Try / catch

try { return converter.ConvertTo(value, typeof(string)); }
catch (NotSupportedException) { return null; /* store bitmap via separate resource mechanism */ }

Prevention

When it happens

Trigger: XAML serialization or designer code calling ConvertTo(instance, typeof(string)) on an ImageSource such as a dynamically rendered DrawingImage or a stream-backed BitmapImage with no UriSource.

Common situations: Serializing visuals created at runtime (images loaded from streams or WriteableBitmap) back to XAML; designer round-tripping controls whose ImageSource was set programmatically without a URI.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/69eb9780a2f1c9bc. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/ImageSourceConverter.cs:197

        /// </exception>
        /// <param name="context"> The ITypeDescriptorContext for this call. </param>
        /// <param name="culture"> The CultureInfo which is respected when converting. </param>
        /// <param name="value"> The object to convert to an instance of "destinationType". </param>
        /// <param name="destinationType"> The type to which this will convert the ImageSource instance. </param>
        public override object ConvertTo(ITypeDescriptorContext context, CultureInfo culture, object value, Type destinationType)
        {
            if (destinationType != null && value is ImageSource)
            {
                ImageSource instance = (ImageSource)value;

                if (destinationType == typeof(string))
                {
                    // When invoked by the serialization engine we can convert to string only for some instances
                    if (context != null && context.Instance != null)
                    {
                        if (!instance.CanSerializeToString())
                        {
                            throw new NotSupportedException(SR.Converter_ConvertToNotSupported);
                        }
                    }

                    // Delegate to the formatting/culture-aware ConvertToString method.
                    return instance.ConvertToString(null, culture);
                }
            }

            // Pass unhandled cases to base class (which will throw exceptions for null value or destinationType.)
            return base.ConvertTo(context, culture, value, destinationType);
        }

        /// Try to get a bitmap out of a byte array.  This is an ole format that Access uses.
        /// this fails very quickly so we can try this first without a big perf hit.
        private unsafe Stream GetBitmapStream(byte[] rawData)
        {
            Debug.Assert(rawData != null, "rawData is null.");
            fixed (byte* pByte = rawData)

View on GitHub (pinned to 81131a70a4)