如何在 C# 中使用 XmlDocument 停止空 XML 元素自关闭？

Question

在我被人们说 XML 解析器不应该关心元素是空还是自关闭之前，我之所以不允许自关闭 XML 元素是有原因的。 原因是我实际上使用的是 SGML 而不是 XML，并且我使用的 SGML DTD 非常严格并且不允许这样做。

我拥有的是运行 XSLT 所需的数千个 SGML 文件。 因此，为了应用 XSLT，我不得不暂时将 SGML 转换为 XML。 然后，我编写了一个将它们转换回 SGML 的方法（基本上只是用 SGML 声明替换 XML 声明并写回任何其他实体声明，例如图形实体）。

我的问题是，在转换回 SGML 后，当我在 SGML 编辑器中打开文件时，文件不会解析，因为空元素已自行关闭。

有人知道我在使用 XmlDocument 时如何阻止这种情况发生吗？

将 SGML 转换为 XML 并再次返回的方法如下所示

//converts the SGML file to XML – it’s during this conversion that the 
//empty elements get self-closed, i think

private XmlDocument convertToXML(TextReader reader)
        {
            // setup SgmlReader
            Sgml.SgmlReader sgmlReader = new Sgml.SgmlReader();
            //sgmlReader.DocType = "HTML";
            sgmlReader.WhitespaceHandling = WhitespaceHandling.All;
            sgmlReader.CaseFolding = Sgml.CaseFolding.ToLower;
            sgmlReader.InputStream = reader;


            // create document
            XmlDocument doc = new XmlDocument();
            doc.PreserveWhitespace = true;

            doc.XmlResolver = null;
            doc.Load(sgmlReader);
            return doc;
        }

// method to apply the XSLT stylesheet to the XML document

private void filterApplic(string applicFilter)
        {
            string stylesheet = getRequiredStylesheet(); // do this just once

            if (stylesheet != "")
            {
                foreach (string file in FilesToConvert)
                {
                    fileName = Path.GetFileName(file); //gets just the file name from the path
                    fileNameNoExt = Path.GetFileNameWithoutExtension(file);
                    string ext = Path.GetExtension(file);

                    if (ext == ".sgm")
                    {
                        try
                        {
                            publicIdentifier = getDoctype(file); // gets the sgml declaration
                            entitiesList = getEntitites(file); // gets the list of entities

                            TextReader tr = new StreamReader(file);
                            myDoc = convertToXML(tr);

                            myDoc.Save(outputFolder + "\\temp.xml");

                            var myXslTrans = new XslCompiledTransform();

                            myXslTrans.Load(stylesheet);
                            myXslTrans.Transform(outputFolder + "\\temp.xml", Path.Combine(outputFolder, fileNameNoExt +".xml"));

                            XmlDocument convertedDoc = new XmlDocument();
                           convertedDoc.Load(Path.Combine(outputFolder, fileNameNoExt + ".xml"));

                            convertToSGM(convertedDoc);

                            filesTransformed++;
                        }
                        catch (Exception e)
                        {
                            MessageBox.Show(e.ToString());
                        }

                    }
                }
            }
            else
            {
                MessageBox.Show("The stylesheet was retured empty. Cannot perform Applicability filter.");
                return;
            }


            MessageBox.Show("Complete! " + filesTransformed.ToString() + " files filtered for " + applicFilter);
        }


//convert files back to SGML
private void convertToSGM(XmlDocument myDoc)
        {

            using (var stringWriter = new StringWriter())
            using (var xmlTextWriter = XmlWriter.Create(stringWriter, settings))
            {

                myDoc.WriteTo(xmlTextWriter);
                xmlTextWriter.Flush();


                string xmltext = stringWriter.GetStringBuilder().ToString();

                xmltext = xmltext.Replace("<?xml version=\"1.0\" encoding=\"utf-16\"?>", "<!DOCTYPE DMODULE " + publicIdentifier + ">");
                xmltext = xmltext.Replace("<?xml version=\"1.0\" encoding=\"utf-8\"?>", "<!DOCTYPE DMODULE " + publicIdentifier + ">");

                if (entitiesList.Count != 0)
                {
                    string entityListAsOne = "";

                    foreach (string entity in entitiesList)
                    {
                        entityListAsOne = entityListAsOne + "\r\n" + entity;
                    }

                    xmltext = xmltext.Replace("//EN\">", "//EN\" [" + entityListAsOne + "]>");
                }

                File.WriteAllText(Path.Combine(outputFolder, fileNameNoExt + ".sgm"), xmltext);
            }


        }

Answer 1

一种方法是将适当的XmlWriter子类化并覆盖WriteEndElement()以调用WriteFullEndElement() 。

例如，这里有一个XmlTextWriter的子类版本，它可以完成这项工作：

public class FullElementXmlTextWriter : XmlTextWriter
{
    public FullElementXmlTextWriter(TextWriter w) : base(w) { }

    public FullElementXmlTextWriter(Stream w, Encoding encoding) : base(w, encoding) { }

    public FullElementXmlTextWriter(string filename, Encoding encoding) : base(filename, encoding) { }

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

然后像这样使用它：

string xmltext;
using (var stringWriter = new StringWriter())
{
    using (var xmlTextWriter = new FullElementXmlTextWriter(stringWriter))
    {
        myDoc.WriteTo(xmlTextWriter);
    }
    xmltext = stringWriter.ToString();
}

或者，如果您需要XmlWriterSettings提供的控件，您可以使用装饰器模式将任何XmlWriter封装在装饰器中，该装饰器自动将调用从WriteEndElement()重新映射到WriteFullEndElement() ：

public class FullElementXmlWriterDecorator : XmlWriterDecorator
{
    public FullElementXmlWriterDecorator(XmlWriter baseWriter) : base(baseWriter) { }

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

public class XmlWriterDecorator : XmlWriter
{
    readonly XmlWriter baseWriter;

    public XmlWriterDecorator(XmlWriter baseWriter)
    {
        if (baseWriter == null)
            throw new ArgumentNullException();
        this.baseWriter = baseWriter;
    }

    protected virtual bool IsSuspended { get { return false; } }

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

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

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

    public override void WriteBase64(byte[] buffer, int index, int count)
    {
        if (IsSuspended)
            return;
        baseWriter.WriteBase64(buffer, index, count);
    }

    public override void WriteCData(string text)
    {
        if (IsSuspended)
            return;
        baseWriter.WriteCData(text);
    }

    public override void WriteCharEntity(char ch)
    {
        if (IsSuspended)
            return;
        baseWriter.WriteCharEntity(ch);
    }

    public override void WriteChars(char[] buffer, int index, int count)
    {
        if (IsSuspended)
            return;
        baseWriter.WriteChars(buffer, index, count);
    }

    public override void WriteComment(string text)
    {
        if (IsSuspended)
            return;
        baseWriter.WriteComment(text);
    }

    public override void WriteDocType(string name, string pubid, string sysid, string subset)
    {
        if (IsSuspended)
            return;
        baseWriter.WriteDocType(name, pubid, sysid, subset);
    }

    public override void WriteEndAttribute()
    {
        if (IsSuspended)
            return;
        baseWriter.WriteEndAttribute();
    }

    public override void WriteEndDocument()
    {
        if (IsSuspended)
            return;
        baseWriter.WriteEndDocument();
    }

    public override void WriteEndElement()
    {
        if (IsSuspended)
            return;
        baseWriter.WriteEndElement();
    }

    public override void WriteEntityRef(string name)
    {
        if (IsSuspended)
            return;
        baseWriter.WriteEntityRef(name);
    }

    public override void WriteFullEndElement()
    {
        if (IsSuspended)
            return;
        baseWriter.WriteFullEndElement();
    }

    public override void WriteProcessingInstruction(string name, string text)
    {
        if (IsSuspended)
            return;
        baseWriter.WriteProcessingInstruction(name, text);
    }

    public override void WriteRaw(string data)
    {
        if (IsSuspended)
            return;
        baseWriter.WriteRaw(data);
    }

    public override void WriteRaw(char[] buffer, int index, int count)
    {
        if (IsSuspended)
            return;
        baseWriter.WriteRaw(buffer, index, count);
    }

    public override void WriteStartAttribute(string prefix, string localName, string ns)
    {
        if (IsSuspended)
            return;
        baseWriter.WriteStartAttribute(prefix, localName, ns);
    }

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

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

    public override void WriteStartElement(string prefix, string localName, string ns)
    {
        if (IsSuspended)
            return;
        baseWriter.WriteStartElement(prefix, localName, ns);
    }

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

    public override void WriteString(string text)
    {
        if (IsSuspended)
            return;
        baseWriter.WriteString(text);
    }

    public override void WriteSurrogateCharEntity(char lowChar, char highChar)
    {
        if (IsSuspended)
            return;
        baseWriter.WriteSurrogateCharEntity(lowChar, highChar);
    }

    public override void WriteWhitespace(string ws)
    {
        if (IsSuspended)
            return;
        baseWriter.WriteWhitespace(ws);
    }
}

如果您正在进行异步编写，我相信（但尚未测试）您也想装饰异步方法。

然后像这样使用它：

string xmltext;
using (var stringWriter = new StringWriter())
{
    using (var innerXmlWriter = XmlWriter.Create(stringWriter, settings))
    using (var xmlTextWriter = new FullElementXmlWriterDecorator(innerXmlWriter))
    {
        myDoc.WriteTo(xmlTextWriter);
    }
    xmltext = stringWriter.ToString();
}

小提琴。