dotnet/wpf · error · NotImplementedException

NotImplementedException

Error message

NotImplementedException

What it means

BamlRecordReader.ReadOptimizedStaticContent throws NotImplementedException for the deferring-branch that was never implemented (the SetDeferableContent call is commented out). It performs the ReliableRead into a scratch buffer first, then unconditionally throws, meaning this BAML content-loading path is not supported in the current framework version.

Solutions

  1. Remove or rewrite the XAML so it avoids the optimized deferred static-content path (e.g. non-deferred ResourceDictionary)
  2. Compile and run with the same framework version; check for known fixes in newer .NET releases
  3. Split resource dictionaries so keys are resolved eagerly instead of via optimized static content
  4. If unavoidable, report the repro to the WPF repo — this is a framework limitation, not user error

Example fix

// before: deferred optimized static resource in dictionary
<ResourceDictionary><x:Static Member="lib:Foo.Bar"/></ResourceDictionary>
// after: eager instance resource
<ResourceDictionary><lib:Foo /></ResourceDictionary>
Defensive patterns

Strategy: try-catch

Validate before calling

// avoid constructs that trigger optimized deferred static content; prefer plain StaticResource/direct instances in ResourceDictionary XAML

Try / catch

try { LoadBaml(stream); }
catch (NotImplementedException) {
    // fall back to loading loose XAML via XamlReader.Load on the original .xaml
    return XamlReader.Load(new StringReader(originalXaml));
}

Prevention

When it happens

Trigger: Loading BAML whose optimized static-content section requires reading deferred dictionary values from an in-memory buffer (valuesSize > 0 branch) — the reader reaches ReadOptimizedStaticContent with a deferred-key dictionary whose values must be read from a buffer.

Common situations: BAML produced by toolchains or scenarios that emit buffered optimized static content the runtime reader never implemented; custom BAML tooling or cross-version loading of deferred resource dictionaries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/d32220ed002796b6. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Markup/BamlRecordReader.cs:1707

                BaseReadDeferableContentStart(bamlRecord, out defKeyList, out staticResourceValuesList);

                // If we don't own the stream, someone might close it when the parse is complete,
                // so copy the defer load contents into a buffer.  If we own the
                // stream, then we'll assume the owner will keep it open.
                long endOfKeysPosition = stream.Position;
                Int32 valuesSize = (Int32)(bamlRecord.ContentSize - endOfKeysPosition + startPosition);

                if (!ParserContext.OwnsBamlStream)
                {
                    byte[] buffer = new byte[valuesSize];

                    if (valuesSize > 0)
                    {
                        MS.Internal.IO.Packaging.PackagingUtilities.ReliableRead(
                            BinaryReader, buffer, 0, valuesSize);
                    }

                    throw new NotImplementedException();
                    //dictionary.SetDeferableContent(buffer,
                    //        ParserContext, _rootElement, defKeyList, staticResourceValuesList);
                }
                else
                {
                    throw new NotImplementedException();
                    //dictionary.SetDeferableContent(_bamlStream,
                    //        endOfKeysPosition, valuesSize,
                    //        ParserContext, _rootElement, defKeyList, staticResourceValuesList);

                    //_bamlStream.Seek(valuesSize, SeekOrigin.Current);
                }
            }
        }

        internal void BaseReadDeferableContentStart(
            BamlDeferableContentStartRecord bamlRecord,
            out ArrayList                   defKeyList,

View on GitHub (pinned to 81131a70a4)