dotnet/wpf · error · InvalidOperationException

SR.Format(SR.MarkupExtensionNoContext, GetType().Name…

Error message

SR.Format(SR.MarkupExtensionNoContext, GetType().Name, "IProvideValueTarget")

What it means

ProvideValue needs the WPF XAML parser's IProvideValueTarget service to learn which object/property the extension is being applied to. When the service provider returns null (extension used outside a XAML parse, e.g. in design-time tools or manually constructed markup-extension evaluation), it throws InvalidOperationException naming MarkupExtensionNoContext.

Solutions

  1. Only evaluate the extension through the WPF XAML loader, which supplies IProvideValueTarget.
  2. In custom hosts, provide a service provider implementing IProvideValueTarget that returns the target ResourceDictionary and its Source property.
  3. Construct the theme-sourced dictionary directly in code (set ResourceDictionary.Source to a theme-pack URI) instead of using the extension.

Example fix

// before
var sp = new ServiceProvider(); // no IProvideValueTarget
var uri = (Uri)ext.ProvideValue(sp); // throws
// after
var rd = new ResourceDictionary
{
    Source = new Uri("pack://application:,,,/MyApp;component/Themes/Default.xaml")
};
Defensive patterns

Strategy: try-catch

Validate before calling

var target = serviceProvider?.GetService(typeof(IProvideValueTarget));
if (target == null) throw new InvalidOperationException("ProvideValue requires IProvideValueTarget from a XAML host.");

Type guard

bool HasContext(IServiceProvider sp) => sp?.GetService(typeof(IProvideValueTarget)) is IProvideValueTarget;

Try / catch

try { return (Uri)ext.ProvideValue(sp); }
catch (InvalidOperationException ex) when (ex.Message.Contains("IProvideValueTarget")) { return FallbackUri(); }

Prevention

When it happens

Trigger: Calling ThemeDictionaryExtension.ProvideValue with an IServiceProvider that does not implement IProvideValueTarget; evaluating the extension outside of XAML loading (unit tests, code-generated dictionaries).

Common situations: Unit tests that build ResourceDictionaries in code and evaluate markup extensions manually; custom XAML loaders missing the standard service provider; designer/host environments that partially implement the service provider.

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/9a1e4241ee430ae5. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/ThemeDictionaryExtension.cs:74

        ///  Return an object that should be set on the targetObject's targetProperty
        ///  for this markup extension.  For ThemeDictionaryExtension, this is the Uri
        ///  pointing to theme specific dictionary in the specified assembly by AssemblyName.
        /// </summary>
        /// <param name="serviceProvider">ServiceProvider that can be queried for services.</param>
        /// <returns>
        ///  The object to set on this property.
        /// </returns>
        public override object ProvideValue(IServiceProvider serviceProvider)
        {
            if (string.IsNullOrEmpty(AssemblyName))
            {
                throw new InvalidOperationException(SR.ThemeDictionaryExtension_Name);
            }

            IProvideValueTarget provideValueTarget = serviceProvider.GetService(typeof(IProvideValueTarget)) as IProvideValueTarget;
            if( provideValueTarget == null )
            {
                throw new InvalidOperationException(SR.Format(SR.MarkupExtensionNoContext, GetType().Name, "IProvideValueTarget" ));
            }
                
            object targetObject = provideValueTarget.TargetObject;
            object targetProperty = provideValueTarget.TargetProperty;

            ResourceDictionary dictionary = targetObject as ResourceDictionary;
            PropertyInfo propertyInfo = targetProperty as PropertyInfo;

            // Allow targetProperty to be null or ResourceDictionary.Source
            if (dictionary == null || (targetProperty != null && propertyInfo != SourceProperty))
            {
                throw new InvalidOperationException(SR.ThemeDictionaryExtension_Source);
            }

            Register(dictionary, _assemblyName);
            dictionary.IsSourcedFromThemeDictionary = true;

            return GenerateUri(_assemblyName, SystemResources.ResourceDictionaries.ThemedResourceName, MS.Win32.UxThemeWrapper.ThemeName);

View on GitHub (pinned to 81131a70a4)