通过 StringBuilder 使用 XmlWriter 进行 XML 序列化是 utf-16，而通过 Stream

当我遇到它时，我很惊讶，并编写了一个控制台应用程序来检查它并确保我没有做任何其他事情。

谁能解释一下？

代码如下：

using System;    
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Xml;
using System.Xml.Serialization;
namespace ConsoleApplication1
{
    public class Program
    {
        static void Main(string[] args)
        {
            var o = new SomeObject { Field1 = "string value", Field2 = 8 };
            Console.WriteLine("ObjectToXmlViaStringBuilder");
            Console.Write(ObjectToXmlViaStringBuilder(o));
            Console.WriteLine();
            Console.WriteLine();
            Console.WriteLine("ObjectToXmlViaStream");
            Console.Write(StreamToString(ObjectToXmlViaStream(o)));
            Console.ReadKey();
        }
        public static string ObjectToXmlViaStringBuilder(SomeObject someObject)
        {
            var output = new StringBuilder();
            var settings = new XmlWriterSettings { Encoding = Encoding.UTF8, Indent = true };
            using (var xmlWriter = XmlWriter.Create(output, settings))
            {
                var serializer = new XmlSerializer(typeof(SomeObject));
                var namespaces = new XmlSerializerNamespaces();
                xmlWriter.WriteStartDocument();
                xmlWriter.WriteDocType("Field1", null, "someObject.dtd", null);
                namespaces.Add(string.Empty, string.Empty);
                serializer.Serialize(xmlWriter, someObject, namespaces);
            }
            return output.ToString();
        }
        private static string StreamToString(Stream stream)
        {
            var reader = new StreamReader(stream);
            return reader.ReadToEnd();
        }
        public static Stream ObjectToXmlViaStream(SomeObject someObject)
        {
            var output = new MemoryStream();
            var settings = new XmlWriterSettings { Encoding = Encoding.UTF8, Indent = true };
            using (var xmlWriter = XmlWriter.Create(output, settings))
            {
                var serializer = new XmlSerializer(typeof(SomeObject));
                var namespaces = new XmlSerializerNamespaces();
                xmlWriter.WriteStartDocument();
                xmlWriter.WriteDocType("Field1", null, "someObject.dtd", null);
                namespaces.Add(string.Empty, string.Empty);
                serializer.Serialize(xmlWriter, someObject, namespaces);
            }
            output.Seek(0L, SeekOrigin.Begin);
            return output;
        }
        public class SomeObject
        {
            public string Field1 { get; set; }
            public int Field2 { get; set; }
        }
    }
}

结果如下：

ObjectToXmlViaStringBuilder

<?xml version="1.0" encoding="utf-16"?>
<!DOCTYPE Field1 SYSTEM "someObject.dtd">
<SomeObject>
<Field1>string value</Field1>
<Field2>8</Field2>
</SomeObject>

ObjectToXmlViaStream

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE Field1 SYSTEM "someObject.dtd">
<SomeObject>
<Field1>string value</Field1>
<Field2>8</Field2>
</SomeObject>

        using (MemoryStream memS = new MemoryStream())
        {
            //set up the xml settings
            XmlWriterSettings settings = new XmlWriterSettings();
            settings.OmitXmlDeclaration = OmitXmlHeader;
            using (XmlWriter writer = XmlTextWriter.Create(memS, settings))
            {
                //write the XML to a stream
                xmlSerializer.Serialize(writer, objectToSerialize);
                writer.Close();
            }
            //encode the memory stream to xml
            retString.AppendFormat("{0}", encoding.GetString(memS.ToArray()));
            memS.Close();
        }