如何从XPathNavigator.AppendChild（）创建时设置XmlWriter.XmlWriterSettings？

Question

我需要将XmlWriter的XmlWriterSettings的OmitXmlDeclaration属性设置为false，以便不创建XML声明。问题是我从XPathNavigator.AppendChild（）方法的调用中创建了XmlWriter。代码如下：

public String GetEntityXml<T>(List<T> entities) 
    { 
     XmlDocument xmlDoc = new XmlDocument(); 
     XPathNavigator nav = xmlDoc.CreateNavigator(); 

     using (XmlWriter writer = nav.AppendChild()) 
     { 

      XmlSerializer ser = new XmlSerializer(typeof(List<T>), new XmlRootAttribute(typeof(T).Name + "_LIST")); 
      ser.Serialize(writer, entities); 
     } 

     StringWriter stringWriter = new StringWriter(); 
     XmlTextWriter xmlTextWriter = new XmlTextWriter(stringWriter); 

     xmlDoc.WriteTo(xmlTextWriter); 

     string resultString = stringWriter.ToString(); 

     stringWriter.Close(); 
     xmlTextWriter.Close(); 

     return resultString; 
    } 

任何想法如何序列化列表，并没有XML声明？

Answer 1

我在执行代码时没有获取XML声明。序列化List<int>给我：

<Int32_LIST xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
      xmlns:xsd="http://www.w3.org/2001/XMLSchema"> 
    <int>5</int> 
    <int>7</int> 
    <int>2</int> 
</Int32_LIST> 

注意“XML声明”是OmitXmlDeclaration是指通常类似于：

<?xml version="1.0" encoding="UTF-8" ?> 

如果你不是指xmlns部分，那么这些被称为“XML 名称空间声明”，并且可以通过使用默认空名称空间初始化XmlSerializerNamespaces实例并将其传递到Serialize方法来消除：

XmlSerializer ser = new XmlSerializer(typeof(List<T>), new XmlRootAttribute(typeof(T).Name + "_LIST")); 
var namespaces = new XmlSerializerNamespaces(new[] { new XmlQualifiedName("", "") }); 
ser.Serialize(writer, entities, namespaces); 

下面是一个缩短实现其达到相同的结果代码：

public String GetEntityXml<T>(List<T> entities) 
{ 
    var sb = new StringBuilder(); 
    var settings = new XmlWriterSettings { OmitXmlDeclaration = true }; 
    using (XmlWriter writer = XmlWriter.Create(sb, settings)) 
    { 
     XmlSerializer ser = new XmlSerializer(typeof(List<T>), new XmlRootAttribute(typeof(T).Name + "_LIST")); 
     var namespaces = new XmlSerializerNamespaces(new[] { new XmlQualifiedName("", "") }); 
     ser.Serialize(writer, entities, namespaces); 
    } 
    return sb.ToString(); 
} 

Answer 2

试试这个办法（切换到var的可读性）：

public String GetEntityXml<T>(List<T> entities) 
{ 
    var xmlDoc = new XmlDocument(); 
    var nav = xmlDoc.CreateNavigator(); 
    using (var sw = new StringWriter()) 
    { 
     //Create an XmlWriter that will omit xml declarations 
     var s = new XmlWriterSettings{ OmitXmlDeclaration = true }; 
     using (var xmlWriter = XmlWriter.Create(sw, s)) 
     { 
      //Use the following to serialize without namespaces 
      var ns = new XmlSerializerNamespaces(); 
      ns.Add("", ""); 
      var ser = new XmlSerializer(typeof(List<T>), 
          new XmlRootAttribute(typeof(T).Name + "_LIST")); 
      ser.Serialize(xmlWriter, entities, ns); 
     } 

     //Pass xml string to nav.AppendChild() 
     nav.AppendChild(sw.ToString()); 
    } 

    using (var stringWriter = new StringWriter()) 
    { 
     using (var xmlTextWriter = XmlWriter.Create(stringWriter)) 
     { 
      xmlDoc.WriteTo(xmlTextWriter); 
     } 
     return stringWriter.ToString(); 
    } 
} 

而不是使用nav.AppendChild()创建XmlWriter，您可以分别创建XmlWriter，然后只用nav.AppendChild(string)到XML写入xmlDoc。当您自己创建XmlWriter时，可以省略XML声明。另外，当你序列化时，你可能想要使用XmlSerializerNamespaces类来省略xmlns:xsi和xmlns:xsd命名空间。