XML序列化父/子元素命名空间配置问题：重复父元素解决求助

问题说明 #

XML序列化时配置命名空间后，生成的XML出现嵌套重复的parentElement，期望仅保留一个parentElement，并正确嵌套childElement及其子元素。

示例代码 #

using System;
using System.IO;
using System.Xml.Serialization;

namespace XmlSerializationExample
{
    class Program
    {
        static void Main(string[] args)
        {
            var grandchild = new grandchild_element { Value = "randomResults" };
            var child = new child_element { grandchildElement = grandchild };
            var parent = new parent_element { childElement = child };

            var serializer = new XmlSerializer(typeof(parent_element), "www.testing.com");
            var namespaces = new XmlSerializerNamespaces(new[]
            {
                new XmlQualifiedName("xsi", "http://www.w3.org/2001/XMLSchema-instance")
            });
            var settings = new XmlWriterSettings
            {
                OmitXmlDeclaration = true,
                Indent = true,
                Encoding = System.Text.Encoding.UTF8
            };

            string xmlOutPut = @"C:\Users\[user]\Desktop\xml_test_file_" + DateTime.Now.ToString("HHmmss") + ".xml";

            using (var fileStream = new FileStream(xmlOutPut, FileMode.Create))
            using (var xmlWriter = XmlWriter.Create(fileStream, settings))
            {
                xmlWriter.WriteStartElement("parentElement", "www.testing.com");

                serializer.Serialize(xmlWriter, parent, namespaces);

                xmlWriter.WriteEndElement();
            }
        }
    }

    [XmlRoot(ElementName = "parentElement", Namespace = "www.testing.com")]
    public class parent_element
    {
        public child_element childElement { get; set; }
    }

    public class child_element
    {
        [XmlElement(ElementName = "grandchildElement")]
        public grandchild_element grandchildElement { get; set; }

        [XmlAttribute(AttributeName = "xsi", Namespace = "http://www.w3.org/2000/xmlns/")]
        public string xsi = "http://www.w3.org/2001/XMLSchema-instance";

        [XmlAttribute(AttributeName = "type", Namespace = "http://www.w3.org/2001/XMLSchema-instance")]
        public string type = "text_type";
    }

    public class grandchild_element
    {
        [XmlText]
        public string Value { get; set; }
    }
}

当前输出 #

<parentElement xmlns="www.testing.com">

  <parentElement xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">

    <childElement xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:type="text_type">

      <grandchildElement>randomResults</grandchildElement>

    </childElement>

  </parentElement>

</parentElement>

期望输出 #

<parentElement xmlns="www.testing.com">

    <childElement xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:type="text_type">

      <grandchildElement>randomResults</grandchildElement>

    </childElement>

</parentElement>

修复方案 #

1. 核心问题定位 #

重复的parentElement是因为手动调用xmlWriter.WriteStartElement/WriteEndElement生成了一个父元素，同时XmlSerializer.Serialize会自动序列化parent_element类对应的父元素，导致嵌套重复。

2. 修复步骤 #

步骤1：移除手动写入的父元素标签

删除代码中手动创建parentElement的两行代码，让序列化器完整输出整个结构：

// 移除以下两行
xmlWriter.WriteStartElement("parentElement", "www.testing.com");
xmlWriter.WriteEndElement();

步骤2：优化命名空间配置

移除child_element类中手动定义的xsi命名空间属性，避免重复声明。如果需要让xsi命名空间仅出现在childElement上，可通过XmlNamespaceDeclarations属性在child_element类中单独声明：

public class child_element
{
    [XmlElement(ElementName = "grandchildElement")]
    public grandchild_element grandchildElement { get; set; }

    [XmlNamespaceDeclarations]
    public XmlSerializerNamespaces Namespaces = new XmlSerializerNamespaces(new[]
    {
        new XmlQualifiedName("xsi", "http://www.w3.org/2001/XMLSchema-instance")
    });

    [XmlAttribute(AttributeName = "type", Namespace = "http://www.w3.org/2001/XMLSchema-instance")]
    public string type = "text_type";
}

同时序列化时不传递全局的namespaces参数，确保xsi命名空间仅出现在childElement标签上。

修复后完整代码 #

using System;
using System.IO;
using System.Xml.Serialization;

namespace XmlSerializationExample
{
    class Program
    {
        static void Main(string[] args)
        {
            var grandchild = new grandchild_element { Value = "randomResults" };
            var child = new child_element { grandchildElement = grandchild };
            var parent = new parent_element { childElement = child };

            var serializer = new XmlSerializer(typeof(parent_element), "www.testing.com");
            var settings = new XmlWriterSettings
            {
                OmitXmlDeclaration = true,
                Indent = true,
                Encoding = System.Text.Encoding.UTF8
            };

            string xmlOutPut = @"C:\Users\[user]\Desktop\xml_test_file_" + DateTime.Now.ToString("HHmmss") + ".xml";

            using (var fileStream = new FileStream(xmlOutPut, FileMode.Create))
            using (var xmlWriter = XmlWriter.Create(fileStream, settings))
            {
                serializer.Serialize(xmlWriter, parent);
            }
        }
    }

    [XmlRoot(ElementName = "parentElement", Namespace = "www.testing.com")]
    public class parent_element
    {
        public child_element childElement { get; set; }
    }

    public class child_element
    {
        [XmlElement(ElementName = "grandchildElement")]
        public grandchild_element grandchildElement { get; set; }

        [XmlNamespaceDeclarations]
        public XmlSerializerNamespaces Namespaces = new XmlSerializerNamespaces(new[]
        {
            new XmlQualifiedName("xsi", "http://www.w3.org/2001/XMLSchema-instance")
        });

        [XmlAttribute(AttributeName = "type", Namespace = "http://www.w3.org/2001/XMLSchema-instance")]
        public string type = "text_type";
    }

    public class grandchild_element
    {
        [XmlText]
        public string Value { get; set; }
    }
}

修复后输出 #

<parentElement xmlns="www.testing.com">
    <childElement xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:type="text_type">
        <grandchildElement>randomResults</grandchildElement>
    </childElement>
</parentElement>

内容的提问来源于stack exchange，提问作者learning