为了使Dictionary序列化的XML更加整洁，我编写了一个实现的自定义类IXmlSerializable。
我的自定义类的定义如下：
public class MyCollection : System.Collections.Generic.Dictionary<string, string>, IXmlSerializable
{
private const string XmlElementName = "MyData";
private const string XmlAttributeId = "Id";
public XmlSchema GetSchema()
{
return null;
}
public void ReadXml(XmlReader reader)
{
reader.MoveToContent();
while (reader.Read())
{
if(reader.LocalName == XmlElementName)
{
var tag = reader.GetAttribute(XmlAttributeId);
var content = reader.ReadElementContentAsString();
this.Add(tag, content);
}
}
}
public void WriteXml(System.Xml.XmlWriter writer)
{
foreach (string key in this.Keys)
{
writer.WriteStartElement(XmlElementName);
writer.WriteAttributeString(XmlAttributeId, key);
writer.WriteString(this[key]);
writer.WriteEndElement();
}
}
}
我的代码与此XML代码段一起工作：
<MyCollection xmlns="http://schemas.datacontract.org/2004/07/MyProject" xmlns:i="http://www.w3.org/2001/XMLSchema-instance">
<MyData Id="1">some content</MyData>
<MyData Id="2">some other content</MyData>
</MyCollection>
但是，当我拥有这个缩小的XML时，我的代码将引发异常：
<MyCollection xmlns="http://schemas.datacontract.org/2004/07/MyProject" xmlns:i="http://www.w3.org/2001/XMLSchema-instance"><MyData Id="1">some content </MyData><MyData Id="2">some other content</MyData></MyCollection>
例外是：
System.InvalidOperationException: The ReadElementContentAsString method is not supported on node type EndElement
引发了对的调用ReadElementContentAsString。
如何修复我的代码？
我可以使用以下命令来重现该问题：
var xml = @"<MyCollection xmlns=""http://schemas.datacontract.org/2004/07/MyProject"" xmlns:i=""http://www.w3.org/2001/XMLSchema-instance""><MyData Id=""1"">some content </MyData><MyData Id=""2"">some other content</MyData></MyCollection>";
var raw = Encoding.UTF8.GetBytes(xml);
var serializer = new DataContractSerializer(typeof(MyCollection));
using (var ms = new MemoryStream(raw))
{
var result = serializer.ReadObject(ms); // Exception throws here
}
您的问题是reader.ReadElementContentAsString()将阅读器放置在下一个节点的开头，而不是当前节点的结尾。然后，您随后的无条件调用将reader.Read()消耗该下一个节点。当该节点为空白时，不会造成任何危害，但是当该节点为元素时，将跳过该元素。
您的以下版本MyCollection可解决此问题：
public class MyCollection : System.Collections.Generic.Dictionary<string, string>, IXmlSerializable
{
public XmlSchema GetSchema()
{
return null;
}
public void ReadXml(XmlReader reader)
{
using (var subReader = reader.ReadSubtree())
{
XmlKeyValueListHelper.ReadKeyValueXml(subReader, this);
}
// Consume the EndElement also (or move past the current element if reader.IsEmptyElement).
reader.Read();
}
public void WriteXml(System.Xml.XmlWriter writer)
{
XmlKeyValueListHelper.WriteKeyValueXml(writer, this);
}
}
public static class XmlKeyValueListHelper
{
private const string XmlElementName = "MyData";
private const string XmlAttributeId = "Id";
public static void WriteKeyValueXml(System.Xml.XmlWriter writer, ICollection<KeyValuePair<string, string>> collection)
{
foreach (var pair in collection)
{
writer.WriteStartElement(XmlElementName);
writer.WriteAttributeString(XmlAttributeId, pair.Key);
writer.WriteString(pair.Value);
writer.WriteEndElement();
}
}
public static void ReadKeyValueXml(System.Xml.XmlReader reader, ICollection<KeyValuePair<string, string>> collection)
{
if (reader.IsEmptyElement)
{
reader.Read();
return;
}
reader.ReadStartElement(); // Advance to the first sub element of the list element.
while (reader.NodeType != XmlNodeType.EndElement)
{
if (reader.NodeType == XmlNodeType.Element && reader.LocalName == XmlElementName)
{
var tag = reader.GetAttribute(XmlAttributeId);
string content;
if (reader.IsEmptyElement)
{
content = string.Empty;
// Move past the end of item element
reader.Read();
}
else
{
// Read content and move past the end of item element
content = reader.ReadElementContentAsString();
}
collection.Add(new KeyValuePair<string, string>(tag, content));
}
else
{
// For instance a comment.
reader.Skip();
}
}
// Move past the end of the list element
reader.ReadEndElement();
}
}
一些注意事项：
通过使用，XmlReader.ReadSubtree()我确保ReadXml()不会读到MyCollection元素的末尾，从而破坏将来的元素-在实现时容易犯一个错误IXmlSerializable。
通过检查，reader.NodeType == XmlNodeType.Element && reader.LocalName == XmlElementName我忽略了意外类型的节点，例如注释。
工作。净提琴。
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