dotnet/wpf · error · InvalidOperationException

SR.XamlXmlWriterWriteNotSupportedInCurrentState…

Error message

SR.XamlXmlWriterWriteNotSupportedInCurrentState (WriteGetObject)

What it means

XamlXmlWriter.WriteGetObject throws InvalidOperationException naming "WriteGetObject" when the writer's current state does not allow starting a collection/dictionary get-object, i.e. the current member position cannot implicitly obtain an object value.

Solutions

Only call WriteGetObject after WriteStartMember for a property whose getter returns a collection/dictionary.
Ensure WriteStartObject was called for the parent before WriteGetObject.
Use WriteGetObject only via a XamlReader-driven loop mirroring the source node stream.

Example fix

// before: WriteGetObject with no member open
writer.WriteGetObject();
// after
writer.WriteStartObject(parentType);
writer.WriteStartMember(itemsProperty);
writer.WriteGetObject();

Defensive patterns

Strategy: try-catch

Validate before calling

bool canGet = lastNode == XamlNodeType.StartMember && currentMember.Type is { } mt &&
    (mt.IsCollection || mt.IsDictionary);

Try / catch

try { writer.WriteGetObject(); }
catch (InvalidOperationException ex) when (ex.Message.Contains("WriteGetObject")) { /* ensure member is a collection */ }

Prevention

Verify the current member's XamlType is a collection/dictionary before WriteGetObject.
Only emit WriteGetObject for implicit collection members (property-element syntax).
Mirror the exact node sequence from XamlXmlReader when testing.

When it happens

Trigger: Calling writer.WriteGetObject when not positioned after a member that represents a gettable collection/dictionary property, or when depth/state tracking shows the operation is invalid at this point.

Common situations: Serializing XAML where a collection member is written without the parent object/member structure being opened; custom writers emitting WriteGetObject for non-collection members.

Understand the failure class

Background: "Invalid state transition" errors: "status must be X, actually Y", "already rejected/charging/uninstalled", "cannot ... while running" — what they mean when a library rejects your call — this error's family across 31 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/aa1ed8bdf52e5cd6. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Xaml/XamlXmlWriter.cs:2065

                {
                    writer.ppStateInfo.Writer.WriteStartObject(type);
                    ThrowIfFailed(writer.ppStateInfo.Writer.Failed, "WriteStartObject");

                    XamlNode node = new XamlNode(XamlNodeType.StartObject, type);
                    if (writer.ppStateInfo.CurrentDepth == 0)
                    {
                        writer.ppStateInfo.NodesList.Add(new List<XamlNode> { node });
                    }
                    else
                    {
                        writer.ppStateInfo.NodesList[writer.ppStateInfo.NodesList.Count - 1].Add(node);
                    }

                    writer.ppStateInfo.CurrentDepth++;
                }
                else
                {
                    throw new InvalidOperationException(SR.Format(SR.XamlXmlWriterWriteNotSupportedInCurrentState, "WriteGetObject"));
                }
            }

            public override void WriteEndObject(XamlXmlWriter writer)
            {
                writer.ppStateInfo.Writer.WriteEndObject();
                ThrowIfFailed(writer.ppStateInfo.Writer.Failed, "WriteEndObject");

                XamlNode node = new XamlNode(XamlNodeType.EndObject);

                Debug.Assert(writer.ppStateInfo.CurrentDepth != 0);
                Debug.Assert(writer.ppStateInfo.NodesList.Count != 0);
                writer.ppStateInfo.NodesList[writer.ppStateInfo.NodesList.Count - 1].Add(node);
                writer.ppStateInfo.CurrentDepth--;
            }

            public override void WriteStartMember(XamlXmlWriter writer, XamlMember property)
            {

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