dotnet/wpf · error · IOException

SR.Format(SR.UnableToLocateResource, _name)

Error message

SR.Format(SR.UnableToLocateResource, _name)

What it means

GetStreamCore asks the ResourceManagerWrapper for a stream named _name; if the resource manager cannot locate that resource it returns null and the part throws IOException with SR.UnableToLocateResource naming the missing resource. This is the library's way of reporting a missing embedded resource.

Solutions

1. Verify the resource exists: check the assembly with ildasm/ILSpy for the exact embedded resource name
2. Ensure the file's Build Action is Page or Resource in the project file
3. Fix casing/spelling in the pack URI — resource lookups are case-sensitive
4. Deploy required satellite/localized assemblies alongside the app

Example fix

// before
var uri = new Uri("pack://application:,,,/MyApp;component/views/mypage.xaml"); // file is Views/MyPage.xaml, not embedded
// after
<!-- csproj --> <Page Include="Views\MyPage.xaml" />  // then the URI resolves

bool ResourceExists(Assembly asm, string name) => asm.GetManifestResourceNames().Any(n => n.EndsWith(name, StringComparison.OrdinalIgnoreCase));

try { var s = part.GetStream(); } catch (IOException ex) when (ex.Message.Contains("Unable to locate")) { /* fix resource name/build action */ }

When it happens

Trigger: Requesting a resource part stream via GetStream()/GetStreamCore where the resource name does not exist in the assembly (missing .baml/.xaml resource, wrong casing, resource not embedded).

Common situations: Missing Build Action=Page/Resource in the csproj so the .baml was never embedded; renamed file without updating the pack URI; satellite assembly not deployed; pack URI case mismatch.

Understand the failure class

Background: 'Could not be found', 'does not exist', 'not found in database': the resource-not-found family when an ID, slug, key, or URI lookup comes back empty — this error's family across 20 libraries.

Related errors

• ArgumentOutOfRangeException(nameof(offset))
• can’t seek on baseStream
• Cannot perform this function on a stream that does not…
• Image_CannotCreateTempFile
• No file exists at

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/aff173f168351d1b. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/MS/Internal/AppModel/ResourcePart.cs:62

        #region Protected Methods

        protected override Stream GetStreamCore(FileMode mode, FileAccess access)
        {
            Stream stream = null;

            stream = EnsureResourceLocationSet();
            // in order to find the resource we might have to open a stream.
            // rather than waste the stream it is returned here and we can use it.
            if (stream == null)
            {
                // Start looking for resources using the current ui culture.
                // The resource manager will fall back to invariant culture automatically.
                stream = _rmWrapper.GetStream(_name);

                if (stream == null)
                {
                    throw new IOException(SR.Format(SR.UnableToLocateResource, _name));
                }
            }

            // 
            // If this is a Baml stream, it will return BamlStream object, which contains
            // both raw stream and the host assembly.
            //
            ContentType curContent = new ContentType(ContentType);

            if (MimeTypeMapper.BamlMime.AreTypeAndSubTypeEqual(curContent))
            {
                BamlStream bamlStream = new BamlStream(stream, _rmWrapper.Assembly);

                stream = bamlStream;
            }

            return stream;
        }

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