What causes "SR.ReachSerializationAsync_NoNgcType" in dotnet/wpf?

Pass an NgcSerializationManagerAsync instance to the NGCSerializerAsync constructor.

dotnet/wpf · error · XpsSerializationException

SR.ReachSerializationAsync_NoNgcType

Error message

SR.ReachSerializationAsync_NoNgcType

What it means

The NGCSerializerAsync constructor requires an NgcSerializationManagerAsync; the manager argument is first null-checked and then cast. If the manager is any other NgcBaseSerializationManager-derived type (not the async one), an XpsSerializationException with SR.ReachSerializationAsync_NoNgcType is thrown.

Solutions

Pass an NgcSerializationManagerAsync instance to the NGCSerializerAsync constructor.
If synchronous serialization is intended, use NGCSerializer with the matching synchronous manager instead.
Add a compile-time or factory check so manager type and serializer type always correspond.

Example fix

// before
var serializer = new NGCSerializerAsync(new NgcSerializationManager(stream, false));
// after
var serializer = new NGCSerializerAsync(new NgcSerializationManagerAsync(stream, false));

Defensive patterns

Strategy: type-guard

Validate before calling

if (manager is not NgcSerializationManagerAsync asyncManager)
    throw new ArgumentException("NGCSerializerAsync requires NgcSerializationManagerAsync");

Type guard

bool IsAsyncManager(NgcBaseSerializationManager m) => m is NgcSerializationManagerAsync;

Try / catch

try { var s = new NGCSerializerAsync(manager); }
catch (XpsSerializationException ex) {
    // fall back to NGCSerializer for synchronous managers
}

Prevention

Pair each serializer type with its matching manager type in a factory method.
Avoid mixing sync and async XPS APIs in the same pipeline.
Null-check and type-check the manager before constructing the serializer.

When it happens

Trigger: Constructing new NGCSerializerAsync(manager) where manager is null or is a synchronous NgcSerializationManager (or other manager type) instead of NgcSerializationManagerAsync.

Common situations: Mixing sync and async XPS serialization APIs, e.g. passing a plain NgcSerializationManager to the async serializer after refactoring code from synchronous to asynchronous saving of XPS documents.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/ea9ac8f2039056a8. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/ReachFramework/Serialization/manager/NGCSerializerAsync.cs:34

        /// <summary>
        /// Constructor for class ReachSerializer
        /// </summary>
        /// <param name="manager">
        /// The serializtion manager, the services of which are
        /// used later for the serialization process of the type.
        /// </param>
        public
        NGCSerializerAsync(
            PackageSerializationManager   manager
            )
        {
            ArgumentNullException.ThrowIfNull(manager);

            _serializationManager = manager as NgcSerializationManagerAsync;

            if(_serializationManager == null)
            {
                throw new XpsSerializationException(SR.ReachSerializationAsync_NoNgcType);
            }
        }

        #endregion Constructor

        #region Public Methods


        public
        virtual
        void
        AsyncOperation(
            NGCSerializerContext context
            )
        {
            if(context == null)
            {

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