How to create a XmlDocument using XmlWriter in .NET?

Question

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?

score 94 · Accepted Answer · answered Aug 28 '09 at 14:28

94

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

answered Aug 28 '09 at 14:28

Boaz

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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. – Tomek Szpakowicz Apr 26 '10 at 11:41
Anyone know if the same is possible using xdocument/xelement (using .NET 3.5 so cant load directly from the memorystream) – baileyswalk Mar 23 '11 at 10:14
3

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. – harpo May 23 '11 at 03:47
2

Note one drawback to this is that WriteRaw behaves differently for an XmlWriter based on XPathNavigator — namely, it escapes output. – harpo Jul 23 '11 at 20:09
And finally (since I'm still using this), note that the navigator throws away the `DOCTYPE`. Not sure of a workaround for that. – harpo Dec 16 '13 at 00:03
Doesn't work if you're using `async` versions of the `XmlWriter` methods - you'll just get `System.NotImplementedException`: *The method or operation is not implemented.* – Xharlie Mar 28 '17 at 08:49
1

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! – Glenn Slayden Dec 09 '17 at 00:06

score 11 · Answer 2 · answered Aug 28 '09 at 13:41

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);

answered Aug 28 '09 at 13:41

Thomas Levesque

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Sorry but this doesn't answer the question. I need to use a XmlWriter to generate the XML - not a XmlDocument. – Boaz Aug 28 '09 at 13:46
4

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... – Thomas Levesque Aug 28 '09 at 13:47
Anyway, if you can generate the XML with a XmlWriter, I don't see why you couldn't generate it with a XmlDocument... – Thomas Levesque Aug 28 '09 at 13:48
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+1 to counter pointless downvote. This is a decent answer to the question as asked IMHO – Binary Worrier Aug 28 '09 at 13:48
1

I don't like the answer either. It's the classic SO-problem: "How can I solve this in Javascript only?" -- "Use jQuery!" – Seb Nilsson Aug 28 '09 at 13:50
@Seb Nilsson: what's your point ? Loading the XmlDocument from a Stream has the same issue as parsing a string. And I don't see how it compares to jQuery... – Thomas Levesque Aug 28 '09 at 13:51
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@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 Nilsson Aug 28 '09 at 13:59
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@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) – Binary Worrier Aug 28 '09 at 14:15
1

@Thomas Levesque - apparently it is possible. – Boaz Aug 28 '09 at 14:31
Yes, I thought I had seen something like that, but couldn't remember what it was exactly... – Thomas Levesque Aug 28 '09 at 14:35
1

It's nice to find a supplement answer which goes both ways. I need to convert back and forth due to incorporating two separate assemblies using each method. Thanks! – TamusJRoyce Oct 03 '11 at 18:18
1

i think it is a correct approach, not good for large XML, but this is answering the question and even not to bad of practice, even better then the stated pseudo in the question body. – Tomer W Aug 30 '12 at 12:58
This does not answer the question, let me quote `Many .NET functions use XmlWriter to output/generate xml.` - you can't use this approach to call those functions. – Zarat Jan 24 '19 at 15:25

score 7 · Answer 3 · edited Jul 27 '12 at 11:44

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());

score 4 · Answer 4 · answered Aug 28 '09 at 13:45

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

answered Aug 28 '09 at 13:45

Binary Worrier

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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. – Tomek Szpakowicz Apr 26 '10 at 11:50

score 1 · Answer 5 · answered Aug 28 '09 at 13:46

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

answered Aug 28 '09 at 13:46

Zach Bonham

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This would result in the same inefficiency - reparsing the stream to build a DOM again. – Boaz Aug 28 '09 at 13:47
+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. – stevehipwell Aug 28 '09 at 13:52
Boaz is right, it's basically the same as parsing the XmlDocument from a string – Thomas Levesque Aug 28 '09 at 13:54

How to create a XmlDocument using XmlWriter in .NET?

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