使用 xsi:nil="true" C# 序列化删除 xml 元素

Question

我有一个 XML，它有一些值，有时可能有如下所示的空值：我不希望在 XML 中列出所有具有空值的节点！元素在类中设置为IsNullable = true。任何建议，因为我在 Google 中尝试了很多东西.. 没有任何帮助！

<?xml version="1.0" encoding="utf-8"?>
<Materials>
  <Material>
    <MaterialName>ABC</MaterialName>
    <Weight Value="0.303">
      <Weight_A xsi:nil="true" />
      <Weight_B xsi:nil="true" />
    </Weight>
    <Density Value="800">
      <Density_A xsi:nil="true" />
      <Density_B xsi:nil="true" />
    </Density>
    <Volume Value="8771.427" />
  </Material>
  <Material>
    <MaterialName>ABC</MaterialName>
    <Weight>
      <V5_Weight>2.009</V5_Weight>
      <V6_Weight>1.3318154561904</V6_Weight>
    </Weight>
    <Density>
      <V5_density>1000</V5_density>
      <V6_density>663</V6_density>
    </Density>
    <Volume Value="2008771.427" />
  </Material>
</Materials>

类结构如下：

[XmlRoot(ElementName = "Weight")]
public class Weight
{
    [XmlElement(ElementName = "Weight_A", IsNullable = true)]
    public string Weight_A { get; set; }

    [XmlElement(ElementName = "Weight_B", IsNullable = true)]
    public string Weight_B { get; set; }

    [XmlAttribute(AttributeName = "Value")]
    public string Value { get; set; }

}

[XmlRoot(ElementName = "Density")]
public class Density
{
    [XmlElement(ElementName = "Density_A", IsNullable = true)]
    public string Density_A { get; set; }
    [XmlElement(ElementName = "Density_B", IsNullable = true)]
    public string Density_B { get; set; }

    [XmlAttribute(AttributeName = "Value")]
    public string Value { get; set; }
}

[XmlRoot(ElementName = "Volume")]
public class Volume
{
    [XmlElement(ElementName = "Volume_A")]
    public string Volume_A { get; set; }
    [XmlElement(ElementName = "Volume_B")]
    public string Volume_B { get; set; }

    [XmlAttribute(AttributeName = "Value")]
    public string Value { get; set; }
}

[XmlRoot(ElementName = "Material")]
public class Material
{
    [XmlElement(ElementName = "MaterialName")]
    public string MaterialName { get; set; }
    [XmlElement(ElementName = "Weight")]
    public Weight Weight { get; set; }

    [XmlElement(ElementName = "Density")]
    public Density Density { get; set; }
    [XmlElement(ElementName = "Volume")]
    public Volume Volume { get; set; }
}

[XmlRoot(ElementName = "Materials")]
public class Materials
{
    [XmlElement(ElementName = "Material")]
    public List<Material> Material { get; set; }
}

Answer 1

基本问题是您设置了XmlElementAttribute.IsNullable = true。来自docs：

获取或设置一个值，该值指示XmlSerializer 是否必须将设置为null 的成员序列化为xsi:nil 属性设置为true 的空标记。

因此，理论上您可以将其设置为 false（或根本不设置），并且不会为空值发出 xsi:nil 属性：

[XmlRoot(ElementName = "Weight")]
public class Weight
{
    [XmlElement(ElementName = "Weight_A" /*, IsNullable = true*/)]
    public string Weight_A { get; set; }
    [XmlElement(ElementName = "Weight_B" /*, IsNullable = true*/)]
    public string Weight_B { get; set; }

    [XmlAttribute(AttributeName = "Value")]
    public string Value { get; set; }
}

[XmlRoot(ElementName = "Density")]
public class Density
{
    [XmlElement(ElementName = "Density_A"/*, IsNullable = true*/)]
    public string Density_A { get; set; }
    [XmlElement(ElementName = "Density_B"/*, IsNullable = true*/)]
    public string Density_B { get; set; }

    [XmlAttribute(AttributeName = "Value")]
    public string Value { get; set; }
}

但是，如果您这样做，您可能会遇到反序列化遗留 XML 文件的问题，即字符串值的 xsi:nil 元素现在将被反序列化为空字符串，而不是 null 字符串。 （演示小提琴#1 here。）如果这成为一个问题，您必须保留XmlElementAttribute.IsNullable = true 设置，而是使用this answer 中描述的条件序列化模式之一到ShouldSerialize*() vs *Specified Conditional Serialization Pattern ：

[XmlRoot(ElementName = "Weight")]
public class Weight
{
    [XmlElement(ElementName = "Weight_A", IsNullable = true)]
    public string Weight_A { get; set; }

    public bool ShouldSerializeWeight_A() { return Weight_A != null; }

    [XmlElement(ElementName = "Weight_B", IsNullable = true)]
    public string Weight_B { get; set; }

    public bool ShouldSerializeWeight_B() { return Weight_B != null; }

    [XmlAttribute(AttributeName = "Value")]
    public string Value { get; set; }
}

[XmlRoot(ElementName = "Density")]
public class Density
{
    [XmlElement(ElementName = "Density_A", IsNullable = true)]
    public string Density_A { get; set; }

    public bool ShouldSerializeDensity_A() { return Density_A != null; }

    [XmlElement(ElementName = "Density_B", IsNullable = true)]
    public string Density_B { get; set; }

    public bool ShouldSerializeDensity_B() { return Density_B != null; }

    [XmlAttribute(AttributeName = "Value")]
    public string Value { get; set; }
}

完成此操作后，<NodeName xsi:nil="true" /> 元素将在反序列化期间映射到 null 字符串，并在序列化期间完全跳过。

注意事项：

• 您的 XML 格式不正确。它缺少xsi: 命名空间前缀的定义，可能是因为它是某个较大文档的片段。这个答案假定它应该是：

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

• 某些元素根本不绑定到您的 c# 数据模型，包括：

  <V5_Weight>2.009</V5_Weight>
  <V6_Weight>1.3318154561904</V6_Weight>
  

  和

  <V5_density>1000</V5_density>
  <V6_density>663</V6_density>
  

  这个答案并没有试图解决这个问题（如果它实际上是一个问题）。

小提琴样本 #2 here.