当IXmlSerializable.ReadXml（）中发生架构验证错误时，XmlSerializer为什么会引发异常并引发ValidationEvent。

Question

我已经编写了一些测试来读取XML文件并针对XSD架构对其进行验证。我的数据对象混合使用基于属性和自定义IXmlSerializable的实现，并且使用XmlSerializer进行反序列化。

我的测试包括将未知元素插入XML，以使其不符合架构。然后，我测试验证事件是否触发。

如果未知元素放置在XML中，那么它是基于属性的数据类之一的子元素（即，属性用XmlAttribute和XmlElement属性修饰），则验证会正确触发。

但是，如果将未知元素放在XML中，那么它是IXmlSerializable类之一的子类，那么将抛出System.InvalidOperationException，但仍然会触发验证。

自定义集合的ReadXmlElements中的代码创建一个新的XmlSerializer来读取子项，这是在Deserialize调用中引发InvalidOperationException的地方。

如果我在该调用周围放置try .. catch块，它将陷入无限循环。唯一的解决方案似乎是在顶级XmlSerializer.Deserialize调用周围放置try-catch块（如测试所示）。

有人知道为什么XmlSerializer以这种方式运行吗？理想情况下，我想尝试在引发异常的地方捕获异常，而不是使用顶级异常处理程序，因此还有一个次要问题：如果使用try..catch块，为什么代码会陷入无限循环中？添加到集合类中。

这里是抛出的异常：

System.InvalidOperationException: There is an error in XML document (13, 10). ---> System.InvalidOperationException: There is an error in XML document (13, 10). ---> System.InvalidOperationException: <UnknownElement xmlns='example'> was not expected.
   at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationReaderGroup.Read1_Group()
   --- End of inner exception stack trace ---
   at System.Xml.Serialization.XmlSerializer.Deserialize(XmlReader xmlReader, String encodingStyle, XmlDeserializationEvents events)
   at System.Xml.Serialization.XmlSerializer.Deserialize(XmlReader xmlReader)
   at XmlSerializerTest.EntityCollection~1.ReadXmlElements(XmlReader reader) in C:\source\repos\XmlSerializerTest\XmlSerializerTest\EntityCollection.cs:line 55
   at XmlSerializerTest.EntityCollection~1.ReadXml(XmlReader reader) in C:\Users\NGGMN9O\source\repos\XmlSerializerTest\XmlSerializerTest\EntityCollection.cs:line 41
   at System.Xml.Serialization.XmlSerializationReader.ReadSerializable(IXmlSerializable serializable, Boolean wrappedAny)
   at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationReaderExample.Read2_Example(Boolean isNullable, Boolean checkType)
   at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationReaderExample.Read3_Example()
   --- End of inner exception stack trace ---
   at System.Xml.Serialization.XmlSerializer.Deserialize(XmlReader xmlReader, String encodingStyle, XmlDeserializationEvents events)
   at System.Xml.Serialization.XmlSerializer.Deserialize(XmlReader xmlReader)
   at XmlSerializerTest.StackOverflowExample.InvalidElementInGroupTest() in C:\source\repos\XmlSerializerTest\XmlSerializerTest\XmlSerializerTest.cs:line 35

Schema.xsd

<?xml version="1.0" encoding="utf-8" ?>
<xs:schema xmlns:local="example"
           attributeFormDefault="unqualified"
           elementFormDefault="qualified"
           targetNamespace="example"
           version="1.0"
           xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <!--  Attribute Groups -->
  <xs:attributeGroup name="Identifiers">
    <xs:attribute name="Id"
                  type="xs:string"
                  use="required" />
    <xs:attribute name="Name"
                  type="xs:string"
                  use="required" />
  </xs:attributeGroup>
  <!-- Complex Types -->
  <xs:complexType abstract="true"
                  name="Entity">
    <xs:sequence>
      <xs:element name="Description"
                  type="xs:string"
                  minOccurs="0"
                  maxOccurs="1" />
    </xs:sequence>
    <xs:attributeGroup ref="local:Identifiers" />
  </xs:complexType>
  <xs:complexType name="DerivedEntity">
    <xs:complexContent>
      <xs:extension base="local:Entity">
        <xs:attribute name="Parameter"
                      use="required" />
      </xs:extension>
    </xs:complexContent>
  </xs:complexType>
  <xs:complexType name="Groups">
      <xs:sequence>
          <xs:element name="Group" type="local:Group" minOccurs="0" maxOccurs="unbounded"/>
      </xs:sequence>
  </xs:complexType>
  <xs:complexType name="Group">
    <xs:complexContent>
      <xs:extension base="local:Entity">
        <xs:sequence>
          <xs:element name="DerivedEntity"
                      type="local:DerivedEntity"
                      minOccurs="0"
                      maxOccurs="unbounded" />
        </xs:sequence>
      </xs:extension>
    </xs:complexContent>
  </xs:complexType>
  <!-- Main Schema Definition -->
  <xs:element name="Example">
      <xs:complexType>
          <xs:sequence>
              <xs:element name="Groups"
                          type="local:Groups"
                          minOccurs="1"
                          maxOccurs="1" />
          </xs:sequence>
      </xs:complexType>
  </xs:element>
</xs:schema>

InvalidElementInGroup.xml

<?xml version="1.0"?>
<Example xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns="example">
    <Groups>
        <Group Name="abc" Id="123">
            <DerivedEntity Id="123" Name="xyz" Parameter="ijk">
                <Description>def</Description>
            </DerivedEntity>
            <DerivedEntity Id="234" Name="bob" Parameter="12"/>
        </Group>
        <Group Name="def" Id="124">
            <Description>This is a description.</Description>
        </Group>
        <UnknownElement/>
    </Groups>
</Example>

实施

注意：本示例中显示的代码不是生产代码。我知道我可以只使用支持序列化的List<T>实现，而无需实现IXmlSerializable。

using System;
using System.Collections;
using System.Collections.Generic;
using System.Xml;
using System.Xml.Schema;
using System.Xml.Serialization;

namespace XmlSerializerTest
{
    public class Example
    {
        public Example()
        {
            Groups = new Groups();
        }

        public Groups Groups { get; set; }
    }

    public class Groups : EntityCollection<Group>
    {

    }
    public class Group : Entity, IXmlSerializable
    {
        private EntityCollection<DerivedEntity> entityCollection;

        public Group()
        {
            this.entityCollection = new EntityCollection<DerivedEntity>();
        }

        #region IXmlSerializable Implementation

        public XmlSchema GetSchema()
        {
            return null;
        }

        public void ReadXml(XmlReader reader)
        {
            reader.MoveToContent();

            // Read the attributes
            ReadXmlAttributes(reader);

            // Consume the start element
            bool isEmptyElement = reader.IsEmptyElement;
            reader.ReadStartElement();
            if (!isEmptyElement)
            {
                ReadXmlElements(reader);
                reader.ReadEndElement();
            }
        }

        /// <summary>
        /// Reads the XML elements.
        /// </summary>
        /// <param name="reader">The reader.</param>
        public override void ReadXmlElements(XmlReader reader)
        {
            // Handle the optional base class description element
            base.ReadXmlElements(reader);

            entityCollection.ReadXmlElements(reader);
        }

        public void WriteXml(XmlWriter writer)
        {
            throw new NotImplementedException();
        }

        #endregion
    }

    public class EntityCollection<T> : IXmlSerializable, IList<T> where T : Entity
    {
        private List<T> childEntityField;

        public EntityCollection()
        {
            childEntityField = new List<T>();
        }

        #region IXmlSerializable Implementation

        public XmlSchema GetSchema()
        {
            return null;
        }

        public void ReadXml(XmlReader reader)
        {
            reader.MoveToContent();

            // Read the attributes
            ReadXmlAttributes(reader);

            // Consume the start element
            bool isEmptyElement = reader.IsEmptyElement;
            reader.ReadStartElement();
            if (!isEmptyElement)
            {
                ReadXmlElements(reader);
                reader.ReadEndElement();
            }
        }

        public virtual void ReadXmlAttributes(XmlReader reader)
        {
        }

        public virtual void ReadXmlElements(XmlReader reader)
        {
            XmlSerializer deserializer = new XmlSerializer(typeof(T), "example");
            while (reader.IsStartElement())
            {
                T item = (T)deserializer.Deserialize(reader);  // throws an InvalidOperationException if an unknown element is encountered.
                if (item != null)
                {
                    Add(item);
                }
            }
        }

        public void WriteXml(XmlWriter writer)
        {
            throw new NotImplementedException();
        }
        #endregion

        #region IList Implementation

        public IEnumerator<T> GetEnumerator()
        {
            return childEntityField.GetEnumerator();
        }

        IEnumerator IEnumerable.GetEnumerator()
        {
            return ((IEnumerable)childEntityField).GetEnumerator();
        }

        public void Add(T item)
        {
            childEntityField.Add(item);
        }

        public void Clear()
        {
            childEntityField.Clear();
        }

        public bool Contains(T item)
        {
            return childEntityField.Contains(item);
        }

        public void CopyTo(T[] array, int arrayIndex)
        {
            childEntityField.CopyTo(array, arrayIndex);
        }

        public bool Remove(T item)
        {
            return childEntityField.Remove(item);
        }

        public int Count => childEntityField.Count;

        public bool IsReadOnly => ((ICollection<T>)childEntityField).IsReadOnly;

        public int IndexOf(T item)
        {
            return childEntityField.IndexOf(item);
        }

        public void Insert(int index, T item)
        {
            childEntityField.Insert(index, item);
        }

        public void RemoveAt(int index)
        {
            childEntityField.RemoveAt(index);
        }

        public T this[int index]
        {
            get => childEntityField[index];
            set => childEntityField[index] = value;
        }

        #endregion
    }

    [System.Xml.Serialization.XmlIncludeAttribute(typeof(DerivedEntity))]
    public abstract class Entity
    {

        public string Description { get; set; }

        public string Id { get; set; }

        public string Name { get; set; }

        public virtual void ReadXmlAttributes(XmlReader reader)
        {
            Id = reader.GetAttribute("Id");
            Name = reader.GetAttribute("Name");
        }

        public virtual void ReadXmlElements(XmlReader reader)
        {
            if (reader.IsStartElement("Description"))
            {
                Description = reader.ReadElementContentAsString();
            }
        }
    }

    public class DerivedEntity : Entity
    {
        public string Parameter { get; set; }
    }
}

测试

namespace XmlSerializerTest
{
    using System;
    using System.IO;
    using System.Xml;
    using System.Xml.Schema;
    using System.Xml.Serialization;
    using Microsoft.VisualStudio.TestTools.UnitTesting;

    [TestClass]
    public class StackOverflowExample
    {
        [TestMethod]
        [DeploymentItem(@"Schema.xsd")]
        [DeploymentItem(@"InvalidElementInGroup.xml")]
        public void InvalidElementInGroupTest()
        {
            // Open the file
            FileStream stream = new FileStream("InvalidElementInGroup.xml", FileMode.Open);

            // Configure settings
            XmlReaderSettings settings = new XmlReaderSettings();
            settings.Schemas.Add(null, @"Schema.xsd");
            settings.ValidationType = ValidationType.Schema;
            settings.ValidationEventHandler += OnValidationEvent;

            XmlSerializer xmlDeserializer = new XmlSerializer(typeof(Example), "example");

            // Deserialize from the stream
            stream.Position = 0;
            XmlReader xmlReader = XmlReader.Create(stream, settings);

            try
            {
                Example deserializedObject = (Example)xmlDeserializer.Deserialize(xmlReader);
            }
            catch (Exception e)
            {
                Console.WriteLine("Exception: " + e);
            }
        }

        private void OnValidationEvent(object sender, ValidationEventArgs e)
        {
            Console.WriteLine("Validation Event: " + e.Message);
        }
    }
}

我已经编写了一些测试来读取XML文件并针对XSD架构对其进行验证。我的数据对象混合使用基于属性和自定义IXmlSerializable的实现，并且正在使用...

Answer 1

您的基本问题是，您有一个抽象基类Entity，其继承者

有时