如何在不修改自动生成类时自定义XmlSerializer日期序列化格式

问题背景 #

有从第三方XSD自动生成的partial实体类：

public partial class MyRegistry
{
    public DateTime MyDateTime { get; set; }
}

使用默认XmlSerializer序列化时，日期输出为ISO标准格式：

var myRegistry = new MyRegistry()
{
    MyDateTime = DateTime.Now
};

var serializer = new XmlSerializer(typeof(MyRegistry));

using (var stringWriter = new StringWriter()) 
{
    serializer.Serialize(stringWriter, myRegistry);
    Console.WriteLine(stringWriter.ToString());
}

输出结果：

<?xml version="1.0" encoding="utf-16"?>
<MyRegistry xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <MyDateTime>2024-04-07T12:05:21.9739342+02:00</MyDateTime>
</MyRegistry>

需要将日期格式改为*dd/MM/yyyy hh:mm*，但直接修改自动生成的类会在XSD更新时丢失，因此需寻找无需修改原始类/XSD的解决方案。

解决方案 #

方案1：Partial类扩展 + XmlAttributeOverrides动态配置 #

利用C# partial类的特性，在独立文件中扩展类并添加格式化属性，再通过XmlAttributeOverrides告诉序列化器忽略原日期属性：

1. 创建独立文件扩展partial类：

// 此文件不会被XSD生成工具覆盖
public partial class MyRegistry
{
    [XmlElement("MyDateTime")]
    public string MyDateTimeFormatted
    {
        get => MyDateTime.ToString("dd/MM/yyyy hh:mm");
        set => MyDateTime = DateTime.ParseExact(value, "dd/MM/yyyy hh:mm", null);
    }
}

2. 序列化时应用属性覆盖配置：

var overrides = new XmlAttributeOverrides();
// 标记原MyDateTime属性为XmlIgnore
var ignoreAttrs = new XmlAttributes { XmlIgnore = true };
overrides.Add(typeof(MyRegistry), nameof(MyRegistry.MyDateTime), ignoreAttrs);

// 使用配置好的overrides创建序列化器
var serializer = new XmlSerializer(typeof(MyRegistry), overrides);

var myRegistry = new MyRegistry()
{
    MyDateTime = DateTime.Now
};

using (var stringWriter = new StringWriter())
{
    serializer.Serialize(stringWriter, myRegistry);
    Console.WriteLine(stringWriter.ToString());
}

方案2：自定义XmlTextWriter处理日期格式 #

通过自定义XmlTextWriter，在写入XML时针对性替换指定节点的日期格式：

1. 实现自定义XmlWriter：

public class CustomDateXmlWriter : XmlTextWriter
{
    private string _currentElement;

    public CustomDateXmlWriter(TextWriter writer) : base(writer) { }

    public override void WriteStartElement(string prefix, string localName, string ns)
    {
        _currentElement = localName;
        base.WriteStartElement(prefix, localName, ns);
    }

    public override void WriteString(string text)
    {
        // 仅处理MyDateTime节点的日期格式
        if (_currentElement == "MyDateTime" && DateTime.TryParse(text, out var date))
        {
            base.WriteString(date.ToString("dd/MM/yyyy hh:mm"));
        }
        else
        {
            base.WriteString(text);
        }
    }
}

2. 序列化时使用自定义Writer：

var myRegistry = new MyRegistry()
{
    MyDateTime = DateTime.Now
};

var serializer = new XmlSerializer(typeof(MyRegistry));

using (var stringWriter = new StringWriter())
using (var xmlWriter = new CustomDateXmlWriter(stringWriter))
{
    serializer.Serialize(xmlWriter, myRegistry);
    Console.WriteLine(stringWriter.ToString());
}

内容的提问来源于stack exchange，提问作者Art