如何使用Linq XML强制显式标记关闭？

Question

这与以下问题相同: 使用System.Xml.Linq命名空间的显式元素关闭标记

但我使用Net 4.0,答案不再适用.

问题是我保存标签没有真正的值,我的输出XML看起来像这样:

<field/>

但我需要的是始终打开和关闭标签,即

<field></field>

问题:怎么做？

编辑

1

添加空节点:

if (field_xml == null) // always true, because I create the file for the first time
{
    field_xml = new XElement(XMLKeys.field,String.Empty);
    table_xml.Add(field_xml);
}
field_xml.SetAttributeValue(XMLKeys.name, field_info.Name);
// ... setting some other attributes of this node

然后,保存xml:

var writer = new FullEndingXmlTextWriter(parameters.OutputFilename, Encoding.UTF8);
root_xml.Save(writer);

FullEndingXmlTextWriter是Evil Greebo指出的专门类(它应该强制显式关闭标记).

Answer 1

将XElement值显式设置为空字符串应该有效.LINQ-to-XML已经将没有内容(如new XElement("foo"))的节点与内容长度为零的节点(如)区别开来new XElement("foo", string.Empty),正如您可以从文档中看到的那样XElement.IsEmpty.

但是如果不起作用,或者如果您需要微调XML输出的其他方面,您可以派生自定义XmlWriter:

public class MyWriter : XmlWriter
{
    private readonly XmlWriter inner;
    public MyWriter(XmlWriter inner)
    {
        this.inner = inner;
    }

    public void Dispose()
    {
        ((IDisposable) inner).Dispose();
    }

    public override void WriteStartDocument()
    {
        inner.WriteStartDocument();
    }

    public override void WriteStartDocument(bool standalone)
    {
        inner.WriteStartDocument(standalone);
    }

    public override void WriteEndDocument()
    {
        inner.WriteEndDocument();
    }

    public override void WriteDocType(string name, string pubid, string sysid, string subset)
    {
        inner.WriteDocType(name, pubid, sysid, subset);
    }

    public override void WriteStartElement(string prefix, string localName, string ns)
    {
        inner.WriteStartElement(prefix, localName, ns);
    }

    public override void WriteEndElement()
    {
        inner.WriteFullEndElement();
    }

    public override void WriteFullEndElement()
    {
        inner.WriteFullEndElement();
    }

    public override void WriteStartAttribute(string prefix, string localName, string ns)
    {
        inner.WriteStartAttribute(prefix, localName, ns);
    }

    public override void WriteEndAttribute()
    {
        inner.WriteEndAttribute();
    }

    public override void WriteCData(string text)
    {
        inner.WriteCData(text);
    }

    public override void WriteComment(string text)
    {
        inner.WriteComment(text);
    }

    public override void WriteProcessingInstruction(string name, string text)
    {
        inner.WriteProcessingInstruction(name, text);
    }

    public override void WriteEntityRef(string name)
    {
        inner.WriteEntityRef(name);
    }

    public override void WriteCharEntity(char ch)
    {
        inner.WriteCharEntity(ch);
    }

    public override void WriteWhitespace(string ws)
    {
        inner.WriteWhitespace(ws);
    }

    public override void WriteString(string text)
    {
        inner.WriteString(text);
    }

    public override void WriteSurrogateCharEntity(char lowChar, char highChar)
    {
        inner.WriteSurrogateCharEntity(lowChar, highChar);
    }

    public override void WriteChars(char[] buffer, int index, int count)
    {
        inner.WriteChars(buffer, index, count);
    }

    public override void WriteRaw(char[] buffer, int index, int count)
    {
        inner.WriteRaw(buffer, index, count);
    }

    public override void WriteRaw(string data)
    {
        inner.WriteRaw(data);
    }

    public override void WriteBase64(byte[] buffer, int index, int count)
    {
        inner.WriteBase64(buffer, index, count);
    }

    public override void Close()
    {
        inner.Close();
    }

    public override void Flush()
    {
        inner.Flush();
    }

    public override string LookupPrefix(string ns)
    {
        return inner.LookupPrefix(ns);
    }

    public override WriteState WriteState
    {
        get { return inner.WriteState; }
    }
}

相关方法是这样的:

public override void WriteEndElement()
{
    inner.WriteFullEndElement(); // always write both start and close tags
}

Answer 2

我无法重现你的错误.这在4.0和3.5 netFX中都可以正常工作:

namespace ExplicitXmlClosingTags
{
    using System.Xml;
    using System.Xml.Linq;

    class Program
    {
        static void Main(string[] args)
        {
            const string ElementRoot = "RootElement";
            const string ElementChild = "ChildElement";
            const string AttributeChild = "ChildAttribute";

            XDocument xDoc = new XDocument();
            XElement root = new XElement(ElementRoot);
            XElement child = new XElement(ElementChild, string.Empty);
            root.Add(child);

            child.SetAttributeValue(AttributeChild, "AttrValue");
            xDoc.Add(root);

            XmlWriterSettings xws = new XmlWriterSettings();
            xws.Indent = true;
            using (XmlWriter xw = XmlWriter.Create("out.xml", xws))
            {
                xDoc.Save(xw);    
            }
        }
    }
}

产生以下内容:

<?xml version="1.0" encoding="utf-8"?>
<RootElement>
  <ChildElement ChildAttribute="AttrValue"></ChildElement>
</RootElement>