dotnet/wpf · error · UnauthorizedAccessException

SR.StreamCannotBeWritten

Error message

SR.StreamCannotBeWritten

What it means

Flush() throws UnauthorizedAccessException (SR.StreamCannotBeWritten) when the underlying backing Stream is not writable. The store serializes pending annotations to this stream, so a read-only stream makes flushing impossible.

Solutions

1. Open the stream with write access: new FileStream(path, FileMode.OpenOrCreate, FileAccess.ReadWrite).
2. Check stream.CanWrite before creating/flushing the store and surface a clear error to the user.
3. Copy the annotation store to a writable location and reopen the store over that stream.
4. Remove read-only attributes or fix share/ACL permissions on the store file.

Example fix

// before
var stream = File.OpenRead(storePath);
var store = new XmlStreamStore(stream);
store.Flush();

// after
var stream = File.Open(storePath, FileMode.OpenOrCreate, FileAccess.ReadWrite);
var store = new XmlStreamStore(stream);
store.Flush();

if (!stream.CanWrite) throw new InvalidOperationException("Annotation store stream is read-only; cannot flush.");

try { store.Flush(); }
catch (UnauthorizedAccessException) { /* prompt user to save to a writable location */ }

When it happens

Trigger: Opening a stream with FileAccess.Read / FileMode.Open + read-only FileShare, or wrapping a write-protected file stream, then constructing XmlStreamStore over it and calling Flush() after annotations are marked dirty (or explicitly).

Common situations: Opening the annotation store file from a read-only location or medium (CD/DVD, read-only network share); opening the file while it is locked read-only; passing a MemoryStream that was created from a read-only buffer.

Understand the failure class

Background: "Permission denied" / "Failed to write" file errors: why a library can't write its files to disk (EACCES, EPERM, ENOSPC) and how to fix them — this error's family across 43 libraries.

Related errors

• SR.ReadNotSupported
• SR.UnauthorizedAccessExceptionWithFileName
• ArgumentOutOfRangeException(nameof(offset))
• can’t seek on baseStream
• Exception of type 'UnauthorizedAccessException' was thrown.

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/eeb9ec65cc880880. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Annotations/Storage/XmlStreamStore.cs:363

        /// <summary>
        ///     Causes any buffered data to be written to the underlying
        ///     storage mechanism.  Gets called after each operation if
        ///     AutoFlush is set to true.  The stream is truncated to
        ///     the length of the data written out by the store.
        /// </summary>
        /// <exception cref="UnauthorizedAccessException">stream cannot be written to</exception>
        /// <exception cref="InvalidOperationException">if no stream has been set on the store</exception>
        /// <exception cref="ObjectDisposedException">if object has been disposed</exception>
        /// <seealso cref="AutoFlush"/>
        public override void Flush()
        {
            lock (SyncRoot)
            {
                CheckStatus();
                if (!_stream.CanWrite)
                {
                    throw new UnauthorizedAccessException(SR.StreamCannotBeWritten);
                }

                if (_dirty)
                {
                    SerializeAnnotations();
                    _stream.Position = 0;
                    _stream.SetLength(0);
                    _document.PreserveWhitespace = true;
                    _document.Save(_stream);
                    _stream.Flush();
                    _dirty = false;
                }
            }
        }

        /// <summary>
        /// Returns a list of namespaces that are compatible with an  input namespace
        /// </summary>

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