Reusing XmlTextWriter class

Question

Is it possible to reuse the same instance of XmlTextWriter class for generating more xml documents? I mean something like this:

XmlTextWriter writer = new XmlTextWriter();
writer.WriteStartDocument();
writer.WriteStartElement("Message1");
writer.WriteEndElement();
writer.WriteEndDocument();

// do something with xml created
...

writer.Reset() // ?
writer.WriteStartDocument();
writer.WriteStartElement("Message2");
writer.WriteEndElement();
writer.WriteEndDocument();
// do something with xml created
...

Answer 1

Easy answer: yes, it's possible to do that.

But this would be achived if underlying stream isn't pointing to a file. MemoryStream could be a good example of that.

As MemoryStream saves the stream "in memory", you can write a lot of XML files with your XmlTextWriter and after ending each document, do a MemoryStream.ToArray() and give it as argument for File.WriteAllBytes.

After writing all bytes, you'd clear your memory stream.

You can clear your memory stream by calling MemoryStream.SetLength method and give 0 as length:

• http://msdn.microsoft.com/en-us/library/system.io.memorystream.setlength.aspx

Read more here, about stream overload of XmlTextWriter constructor:

• http://msdn.microsoft.com/en-us/library/ms162588.aspx

And this for File.WriteAllBytes:

• http://msdn.microsoft.com/en-us/library/system.io.file.writeallbytes.aspx

About some concerns when reusing an XmlTextWriter

Some years ago @NigelTouch raised a concern on some comment:

The problem I found is that if an exception is thrown part-way through, for example after WriteStartElement(), then even though you Flush() the Writer and set the Stream length to 0, the Writer remains in a WriteState of Element. When you start the next document, it begins with a closing ">" (for example). Avoid reuse

And some hours ago, @Mike-EEE got into the same issue:

Please provide working code of an example solution. I am running into the same problem as Nigel describes

BTW, a bit of trial-error got me to recover a given XmlTextWriter to reuse it as many times as you want:

    using(MemoryStream stream = new MemoryStream())
    using(StreamReader streamReader = new StreamReader(stream))
    using(XmlTextWriter writer = new XmlTextWriter(stream, Encoding.UTF8))
    {
        writer.WriteStartDocument(true);
        writer.WriteStartElement("a");

        try 
        {
            throw new Exception();
        }
        catch 
        {
            // This line makes de magic: ending the document
            // avoids the issue mentioned by @NigelTouch
            writer.WriteEndDocument();
            writer.Flush();
            stream.SetLength(0);
        }


        writer.WriteStartDocument(true);
        writer.WriteStartElement("b");
        writer.WriteEndElement();
        writer.Flush();

        stream.Position = 0;

        Console.WriteLine(streamReader.ReadToEnd());

    }