SR.Format(SR.ParserCannotConvertPropertyValue, "Value"…

Error message

SR.Format(SR.ParserCannotConvertPropertyValue, "Value", typeof(Object).FullName)

What it means

SetterTriggerConditionValueConverter.ResolveValue needs IXamlSchemaContextProvider from the service provider to convert the 'Value' string of a Setter/Trigger/Condition. If the schema context service is absent, the converter cannot operate, so it throws NotSupportedException indicating it cannot convert the Value property to Object.

Solutions

Ensure conversion happens within the standard WPF XAML load pipeline which supplies IXamlSchemaContextProvider
If calling manually, provide an IServiceProvider that implements GetService(typeof(IXamlSchemaContextProvider))
Use a different conversion mechanism (e.g. TypeDescriptor.GetConverter) when not under XAML parse

Example fix

// before
var converter = new SetterTriggerConditionValueConverter();
var value = converter.ConvertFromString(null); // no schema context service
// after
// let the XAML parser perform the conversion, or supply a proper service provider
var value = (string)xamlSchemaContextClrValue; // convert via schema context when hand-rolling

Defensive patterns

Strategy: try-catch

Validate before calling

var sc = serviceProvider.GetService(typeof(IXamlSchemaContextProvider)) as IXamlSchemaContextProvider;
if (sc == null) throw new InvalidOperationException("Setter/Trigger conversion requires a XAML schema context");

Type guard

bool HasSchemaContext(IServiceProvider sp) => sp?.GetService(typeof(IXamlSchemaContextProvider)) is IXamlSchemaContextProvider;

Try / catch

try { value = converter.ConvertFromString(serviceProvider, valueString); }
catch (NotSupportedException ex) { /* conversion attempted outside XAML parse; use parser or proper service provider */ }

Prevention

Let the WPF XAML parser perform Setter/Trigger Value conversions
Do not call SetterTriggerConditionValueConverter directly with minimal service providers
Provide IXamlSchemaContextProvider when hand-rolling XAML tooling

When it happens

Trigger: Using SetterTriggerConditionValueConverter (the Value of Setter/Trigger/Condition properties) outside of a proper XAML schema context, e.g. calling TypeConverter.ConvertFromString with a bare or incomplete ITypeDescriptorContext/IServiceProvider that doesn't supply IXamlSchemaContextProvider.

Common situations: Invoking the converter directly at runtime without going through the XAML parser; custom tooling that fakes the service provider; parsing Styles with a non-WPF XAML reader lacking schema-context services.

Understand the failure class

Background: "not installed", "pip install", "required for": how missing-dependency errors surface across open-source libraries — this error's family across 34 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/6dffa12c1020ee18. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Markup/SetterTriggerConditionValueConverter.cs:97

        #endregion Public Methods

        internal static object ResolveValue(ITypeDescriptorContext serviceProvider,
            DependencyProperty property, CultureInfo culture, object source)
        {
            ArgumentNullException.ThrowIfNull(serviceProvider);
            ArgumentNullException.ThrowIfNull(source);

            // Only need to type convert strings and byte[]
            if (!(source is byte[] || source is String || source is Stream))
            {
                return source;
            }

            IXamlSchemaContextProvider ixsc = (serviceProvider.GetService(typeof(IXamlSchemaContextProvider))
                as IXamlSchemaContextProvider);
            if (ixsc == null)
            {
                throw new NotSupportedException(SR.Format(SR.ParserCannotConvertPropertyValue, "Value", typeof(Object).FullName));
            }
            XamlSchemaContext schemaContext = ixsc.SchemaContext;

            if (property != null)
            {
                //Get XamlMember from dp
                System.Xaml.XamlMember xamlProperty = 
                    schemaContext.GetXamlType(property.OwnerType).GetMember(property.Name);
                if (xamlProperty == null)
                    xamlProperty = 
                        schemaContext.GetXamlType(property.OwnerType).GetAttachableMember(property.Name);

                System.Xaml.Schema.XamlValueConverter<TypeConverter> typeConverter = null;
                
                if (xamlProperty != null)
                { 
                    // If we have a Baml2006SchemaContext and the property is of type Enum, we already know that the 
                    // type converter must be the EnumConverter.

View on GitHub (pinned to 81131a70a4)