dotnet/wpf · error · ArgumentException

SR.Format(SR.ArgumentPropertyMustNotBeNull,"resourceLocator"…

Error message

SR.Format(SR.ArgumentPropertyMustNotBeNull,"resourceLocator", "OriginalString")

What it means

Application.LoadComponent(Object, Uri) validates the resourceLocator Uri before loading XAML. If the Uri's OriginalString is null it throws ArgumentException describing that resourceLocator.OriginalString must not be null. A Uri object can wrap a null string only via unsafe construction, so this is a defensive argument validation.

Solutions

Ensure the Uri is created from a non-null string, e.g. new Uri("MyPage.xaml", UriKind.Relative)
Guard the caller: skip LoadComponent when uri == null || uri.OriginalString == null
Fix the source of the null OriginalString (deserialization/property initialization)

Example fix

// before
Uri uri = GetUriSomehow(); // OriginalString == null
Application.LoadComponent(page, uri);

// after
var uri = new Uri("MyPage.xaml", UriKind.Relative);
Application.LoadComponent(page, uri);

Defensive patterns

Strategy: validation

Validate before calling

if (uri == null || uri.OriginalString == null)
    throw new ArgumentException("resourceLocator must have a non-null OriginalString");
Application.LoadComponent(component, uri);

Type guard

static bool IsValidLocator(Uri u) => u?.OriginalString != null;

Try / catch

try { Application.LoadComponent(component, uri); }
catch (ArgumentException ex) { Log(ex); LoadFallbackComponent(); }

Prevention

Always construct Uri from literal/validated non-null strings
Validate Uri arguments at component boundaries before calling LoadComponent
Never pass Uris that came from unchecked deserialization

When it happens

Trigger: Passing a Uri instance whose OriginalString is null into LoadComponent(Object component, Uri resourceLocator).

Common situations: Uri created through deserialization or interop with a null backing string; a default(Uri)-like flow assigning an uninitialized value that is later boxed into a property; binding a URI property that was never initialized.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/392d8092f0789f16. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Application.cs:352

            {
                bool canCache;
                return resources.FetchResource(resourceKey, allowDeferredResourceReference, mustReturnDeferredResourceReference, out canCache);
            }
        }

        /// <summary>
        /// Create logic tree from given resource Locator, and associate this
        /// tree with the given component.
        /// </summary>
        /// <param name="component">Root Element</param>
        /// <param name="resourceLocator">Resource Locator</param>
        public static void LoadComponent(Object component, Uri resourceLocator)
        {
            ArgumentNullException.ThrowIfNull(component);
            ArgumentNullException.ThrowIfNull(resourceLocator);

            if (resourceLocator.OriginalString == null)
                throw new ArgumentException(SR.Format(SR.ArgumentPropertyMustNotBeNull,"resourceLocator", "OriginalString"));

            if (resourceLocator.IsAbsoluteUri)
                throw new ArgumentException(SR.AbsoluteUriNotAllowed);

            // Passed a relative Uri here.
            // needs to resolve it to Pack://Application.
            //..\..\ in the relative Uri will get stripped when creating the new Uri and resolving to the
            //PackAppBaseUri, i.e. only relative Uri within the appbase are created here
            Uri currentUri = new Uri(BaseUriHelper.PackAppBaseUri, resourceLocator);

            //
            // Generate the ParserContext from packUri
            //
            ParserContext pc = new ParserContext
            {
                BaseUri = currentUri
            };

View on GitHub (pinned to 81131a70a4)