How can I force XDocument to output “UTF-8” in the declaration line?

Question

The following code produces this output:

Answer 1

This is not a bug in .NET. This is due to you using StringWriter as the target for your XDocument. Since StringWriter internally uses UTF-16, the document must also use UTF-16 as encoding. If you save the XDoc to a stream or a file, it will use UTF-8 as instructed.

For more information, see MSDN information about StringWriter.Encoding:

This property is necessary for some XML scenarios where a header must be written containing the encoding used by the StringWriter. This allows the XML code to consume an arbitrary StringWriter and generate the correct XML header.

Answer 2

Allow me answer my own question, this seems to work:

private static string BuildXmlWithLINQ()
{
    XDocument xdoc = new XDocument
    (
        new XDeclaration("1.0", "utf-8", "yes"),
        new XElement("customers",
            new XElement("customer",
                new XElement("firstName", "Jim"),
                new XElement("lastName", "Smith")
            )
        )
    );
    return xdoc.Declaration.ToString() + Environment.NewLine + xdoc.ToString();
}

Answer 3

You can use the following code as an example

XDocument doc = GetXmlDoc();
using (var stream = new MemoryStream())
{
    doc.Save(stream, SaveOptions.DisableFormatting);
    var docBytes = stream.ToArray();
    File.WriteAllBytes("fileName.xml", docBytes);
}