52

Many .NET functions use XmlWriter to output/generate xml. Outputting to a file/string/memory is a very operation:

XmlWriter xw = XmlWriter.Create(PutYourStreamFileWriterEtcHere);
xw.WriteStartElement("root");
...

Sometimes , you need to manipulate the resulting Xml and would therefore like to load it into a XmlDocument or might need an XmlDocument for some other reason but you must generate the XML using an XmlWriter. For example, if you call a function in a 3rd party library that outputs to a XmlWriter only.

One of the things you can do is write the xml to a string and then load it into your XmlDocument:

StringWriter S = new StringWriter();
XmlWriter xw = XmlWriter.Create(S);
/* write away */
XmlDocument xdoc = new XmlDocument();
xdoc.LoadXml(S.ToString());

However this is inefficient - first you serialize all the xml info into a string, then you parse the string again to create the DOM.

How can you point an XmlWriter to build a XmlDocument directly?

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5 Answers 5

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93

Here's at least one solution:

XmlDocument doc = new XmlDocument(); 
using (XmlWriter writer = doc.CreateNavigator().AppendChild()) 
{ 
    // Do this directly 
     writer.WriteStartDocument(); 
     writer.WriteStartElement("root"); 
     writer.WriteElementString("foo", "bar"); 
     writer.WriteEndElement(); 
     writer.WriteEndDocument();
    // or anything else you want to with writer, like calling functions etc.
}

Apparently XpathNavigator gives you a XmlWriter when you call AppendChild()

Credits go to Martin Honnen on : http://groups.google.com/group/microsoft.public.dotnet.xml/browse_thread/thread/24e4c8d249ad8299?pli=1

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7 Comments

Thanks! It was obvious to me that you'd be able to use XmlWriter as a builder for XmlDocument but I just couldn't find an easy way to do it so I ended up writing to buffer and parsing again. They could've made it a little easier to find.
Anyone know if the same is possible using xdocument/xelement (using .NET 3.5 so cant load directly from the memorystream)
Also note that, as written, the resulting XmlWriter will have a conformance level of Document, so if you do send it as the input to an XSL transform as input (and you're not creating a complete document), you can use new XmlDocument().CreateFragment().CreateNavigator() instead.
Note one drawback to this is that WriteRaw behaves differently for an XmlWriter based on XPathNavigator — namely, it escapes output.
This is totally great.So speedy and elegant to build an XmlDocument without going through String or Stream. A useful example: convert arbitrary WPF runtime instance directly into an XmlDocument representation of the XAML object graph it roots: var xd = new XmlDocument(); var w = xd.CreateNavigator().AppendChild(); XamlWriter.Save(inst, new XamlDesignerSerializationManager(w) { XamlWriterMode = XamlWriterMode.Expression }); (Make sure to use the XamlWriter from System.Windows.Markup) This obviously makes the alternatives look very clunky. Fantastic!
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11

You could do the opposite : build the XmlDocument first using DOM, then write it to a XmlWriter :

XmlDocument xdoc = new XmlDocument();
... // build the document

StringWriter S = new StringWriter();
XmlWriter xw = XmlWriter.Create(S);
xdoc.WriteTo(xw);
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13 Comments

XmlWriter isn't designed to write to a XmlDocument, it's designed to write to a Stream or TextWriter. What you're asking is simply not possible, I'm just suggesting another approach...
+1 to counter pointless downvote. This is a decent answer to the question as asked IMHO
I don't like the answer either. It's the classic SO-problem: "How can I solve this in Javascript only?" -- "Use jQuery!"
@Tomas Levesque: My point is that someone asks a question "How do I solve X" and the answer is "Don't solve X, solve Y instead", when that's not the question. If it's impossible to do, then that's the answer.
@Seb: I strongly disagree. We wouldn't get far as programmers if we stopped every time we needed to get from A to C and there was no direct root. Our profession depends on being able to find the alternative route through B. Thomas is suggesting an alternative approach, honestly I don't understand the vilification of this answer (Yes, I realise this is a community. Yes I have exercised my right to vote on this answer. However I am allowed to express my dissatisfaction with the general response)
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8

You can write xml file using XMLWriter class. Here is example for this.

    XmlWriterSettings objSetting = new XmlWriterSettings();
    objSetting.Indent = true;
    objSetting.NewLineOnAttributes = true;

    System.Text.StringBuilder sb = new System.Text.StringBuilder();


    using (XmlWriter objWriter = XmlWriter.Create(sb, objSetting))
    {
        //Note the artificial, but useful, indenting
        objWriter.WriteStartDocument();

        objWriter.WriteStartElement("books");

        ////////Start Book Element///////

        objWriter.WriteStartElement("book");

        objWriter.WriteStartAttribute("ISBN");
        objWriter.WriteValue("asp1");
        objWriter.WriteEndAttribute();

        objWriter.WriteStartElement("Title");
        objWriter.WriteValue("ASP.NET");
        objWriter.WriteEndElement();

        objWriter.WriteElementString("ReleaseDate", "11/11/2010");

        objWriter.WriteStartElement("Pages");
        objWriter.WriteValue(200);
        objWriter.WriteEndElement(); //price

        objWriter.WriteEndElement(); //book
        ////////End Book Element///////


        ////////Another Element

        ////////Start Book Element///////

        objWriter.WriteStartElement("book");

        objWriter.WriteStartAttribute("ISBN");
        objWriter.WriteValue("c#2");
        objWriter.WriteEndAttribute();

        objWriter.WriteStartElement("Title");
        objWriter.WriteValue("C#.NET");
        objWriter.WriteEndElement();

        objWriter.WriteElementString("ReleaseDate", "10/11/2010");

        objWriter.WriteStartElement("Pages");
        objWriter.WriteValue(500);
        objWriter.WriteEndElement(); 

        objWriter.WriteEndElement(); //book
        ////////End Book Element///////



        objWriter.WriteEndElement(); //books
        objWriter.WriteEndDocument();

    }

    File.WriteAllText(Server.MapPath("BooksList.xml"), sb.ToString());
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Comments

4

The idea behind XmlWriter is to wait until you have finished modifying your data before you start writing.

XmlWriter wasn't built with your situation in mind.

Either

  • Wait until you know what your data is going to be before writing

or

  • Do what you're currently doing
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1 Comment

I disagree. XmlWriter is a nice example of builder pattern and it makes perfect sense to use it to build DOM (XmlDocument or any other implementation). And I have very real use case: I read XML data and transform it using some XslCompiledTransform, which writes to XmlWriter, which directly constructs XmlDocument, which I can process and then write out (possibly applying some other XSLT on output). What's wrong with that? And writing out to stream and then parsing again is: a) pointless (it doesn't help or make design any clearer), b) unnecessary and c) highly inefficient.
1

There is an underlying Stream object that the XmlWriter was writing to, if it was bidirectional (MemoryStream), you could simply re-position it back to -0- and then use the Stream object in the XmlDocument.Load(stream).

HTH,

Z

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3 Comments

This would result in the same inefficiency - reparsing the stream to build a DOM again.
+1 This is the way I would chose to do it over the example given in the question as a string doesn't need to be created as an intermediate.
Boaz is right, it's basically the same as parsing the XmlDocument from a string

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