dotnet/wpf · error · InvalidOperationException

SR.BamlWriterClosed

Error message

SR.BamlWriterClosed

What it means

BamlWriter.WriteStartDocument throws InvalidOperationException(SR.BamlWriterClosed) if the writer was already Closed, and SR.BamlWriterStartDoc if WriteStartDocument was already called. Writers are single-use: once closed, no further document writing is permitted.

Solutions

1. Create a new BamlWriter for each document; writers are single-shot
2. Check _closed/IsClosed before calling WriteStartDocument (guard in caller code)
3. Do not call Close before Serialize completes; use 'using' scoped tightly around a single serialization
4. If serializing many objects, wrap creation in a helper that yields a fresh writer per call

Example fix

// before
var w = new BamlWriter(s); w.Serialize(obj); w.Close(); w.Serialize(obj2);
// after
using (var w1 = new BamlWriter(s1)) w1.Serialize(obj);
using (var w2 = new BamlWriter(s2)) w2.Serialize(obj2);

// guard before use
if (writerIsClosed) throw new InvalidOperationException("Create a new BamlWriter; the current one is closed");

static bool CanStartDocument(BamlWriter w) => !wIsClosed(w); // expose or track _closed in your wrapper

try { writer.WriteStartDocument(); }
catch (InvalidOperationException ex) when (ex.Message.Contains("closed") || ex.Message.Contains("document")) {
    writer = new BamlWriter(stream); // recreate and retry once
}

When it happens

Trigger: Calling WriteStartDocument() after Close()/Dispose, or (via Serialize) reusing a BamlWriter for a second document — _closed flag set from prior Close().

Common situations: Serializing multiple objects by reusing one BamlWriter, calling Serialize after explicitly closing, event-driven code that closes the stream and then tries another write.

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

• SR.BamlReaderClosed
• SR.ParserMultiBamls
• Can't Assign to Known Type attributes
• Could not find prefix for type
• Current DocumentSequence, FixedDocument, or FixedPage not…

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/ce67b386085d44c1. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Markup/BamlWriter.cs:145

        }
        

#endregion IParserHelper

#region Record Writing

        /// <summary>
        /// Write the start of document record, giving the baml version string
        /// </summary>
        /// <remarks>
        /// This must be the first call made when creating a new baml file.  This
        /// is needed to specify the start of the document and baml version.
        /// </remarks>
        public void WriteStartDocument()
        {
            if (_closed)
            {
                throw new InvalidOperationException(SR.BamlWriterClosed);
            }
            if (_startDocumentWritten)
            {
                throw new InvalidOperationException(SR.BamlWriterStartDoc);
            }
            
            XamlDocumentStartNode node = new XamlDocumentStartNode(0,0,_depth);
            _bamlRecordWriter.WriteDocumentStart(node);
            _startDocumentWritten = true;
            Push(BamlRecordType.DocumentStart);
        }

        /// <summary>
        /// Write the end of document record.
        /// </summary>
        /// <remarks>
        /// This must be the last call made when creating a new baml file.
        /// </remarks>

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