如何将对象序列化为XDocument?

您可以直接在xdocument中创建一个xmlwriter:

XDocument doc = new XDocument();
using (var writer = doc.CreateWriter())
{
    // write xml into the writer
    var serializer = new DataContractSerializer(objectToSerialize.GetType());
    serializer.WriteObject(writer, objectToSerialize);
}
Console.WriteLine(doc.ToString());