dotnet/wpf · error · NotSupportedException

SR.Converter_ConvertToNotSupported

Error message

SR.Converter_ConvertToNotSupported

What it means

This SR resource string backs a NotSupportedException thrown by generated TypeConverter ConvertTo code for animatable WPF resource types (mcg generator, ManagedResource.cs). Animatable resources must be frozen before conversion; the generated converter refuses to convert instances whose CanFreeze is true but are not frozen. It signals that the requested type conversion is not supported for this resource instance in its current state.

Solutions

1. Freeze the resource (or make it immutable) before invoking the converter, so CanFreeze is false
2. Verify the resource type actually supports ConvertTo conversion; use a converter intended for the target type
3. If you own the mcg resource definition, mark the resource as not animatable or provide a custom TypeConverter
4. Catch NotSupportedException and fall back to manual serialization of the resource

Example fix

// before
object v = converter.ConvertTo(resource, typeof(string)); // throws if unfrozen
// after
if (resource.CanFreeze) resource.Freeze();
object v = converter.ConvertTo(resource, typeof(string));

if (resource.CanFreeze) resource.Freeze();
// ConvertTo is now safe for animatable resources

try { return converter.ConvertTo(value, targetType); }
catch (NotSupportedException) { return manualSerialize(value); }

When it happens

Trigger: Calling TypeConverter.ConvertTo on a generated wrapper for an animatable resource (resource.IsAnimatable) when the instance reports CanFreeze == true (i.e. it is still freezable/unfrozen and therefore mutable).

Common situations: Using the design-time or serialization converter on an unfrozen Animatable-derived resource (e.g. a Brush or DoubleAnimation wrapper) during XAML serialization or tooling; passing a freshly created, never-frozen instance to a converter.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

• SR.Converter_ConvertToNotSupported
• Cannot convert from type.
• Cannot convert to type.
• Converter_ConvertToNotSupported
• General_Expected_Type (ImageSource)

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/d7b07f117a43dc77. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/WpfGfx/codegen/mcg/generators/ManagedResource.cs:2771

            if (resource.IsAbstract)
            {
                return
                    [[inline]]internal abstract InstanceDescriptor ToInstanceDescriptor();[[/inline]];
            }

            if (resource.IsCollection)
            {
                StringCodeSink notSupportedCheck = new StringCodeSink();
                string modifiers = "";

                if (resource.IsAnimatable)
                {
                    notSupportedCheck.Write(
                        [[inline]]
                            if (!CanFreeze)
                            {
                                throw new NotSupportedException(SR.Converter_ConvertToNotSupported);
                            }
                        [[/inline]]
                    );
                }

                if (resource.Extends != null)
                {
                    modifiers = "override";
                }

                // Override if derived from parent class.  If abstract provide abstract implementation.

                return
                    [[inline]]
                        internal [[modifiers]] InstanceDescriptor ToInstanceDescriptor()
                        {
                            [[notSupportedCheck]]

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