Programmatically format XML in indented form just like Visual Studio's auto-format

Question

I haven't found a way using .NET's XmlWriter and associated XmlWriterSettings to format an XML string in indented form exactly the way that Visual Studio does it with its auto-format command (Ctrl-E Ctrl-D, or, depending on keyboard mapping, Ctrl-K Ctrl-D).

I would like to do this because I habitually auto-format all my files in VS, both code and .config files. I have an installer app that updates .config files, and I would like to see actual diffs instead of the entire document changed.

I haven't explored all the different formatting options for auto-format, but I like each XML attribute to be on a separate line, with the first on the same line as the opening tag and subsequent ones lined up with the first, like this:

<asset assetId="12345"
       bucket="default"
       owner="nobody">
  <file path="\\localhost\share\assetA.mov"/>
  <metadata metadataId="23456"
            key="asset_type"
            value="video"/>
</asset>

I've tried formatting with XmlWriterSettings properties 'NewLineHandling = NewLineHandling.None' and 'NewLineOnAttributes = true', but that puts the first attribute below the opening tag and all attributes have the same indentation regardless of the # of characters in the element name, like this:

<asset
  assetId="12345"
  bucket="default"
  owner="nobody">
  <file
    path="\\localhost\share\assetA.mov" />
  <metadata metadataId="23456"
    key="asset_type"
    value="video" />
</asset>

Notice that the standard XmlWriter also ends attribute-only elements with " />" (extra space before the slash), which I dislike but not sure if that's the XML standard. I would think that Visual Studio uses the same API options readily available to developers, but I've yet to find those magical settings. Anyway, here's my format method:

public static string FormatXml( string xmlString, bool indented )
{
    using ( TextReader textReader = new StringReader( xmlString ) )
    using ( XmlReader xmlReader = new XmlTextReader( textReader ) )
    {
        using ( TextWriter textWriter = new StringWriter() )
        {
            var settings = new XmlWriterSettings();
            if ( indented )
            {
               settings.Indent = true;
               settings.IndentChars = "  ";
               settings.NewLineOnAttributes = true;
               settings.NewLineHandling = NewLineHandling.None;
            }
            using ( var xmlWriter = XmlWriter.Create( textWriter, settings ) )
            {
                while ( xmlReader.Read() )
                    xmlWriter.WriteNode( xmlReader, false );
            }
            return textWriter.ToString();
        }
    }
}

Answer 1

I had misunderstood the question. Actually I don't know if there is a way to align the attributes in the way you shown. You could try to implement it yourself, something like this:

    public static string FormatXml(string xmlString, bool indented)
    {
        using (TextReader textReader = new StringReader(xmlString))
        using (XmlReader xmlReader = new XmlTextReader(textReader))
        {
            using (TextWriter textWriter = new StringWriter())
            {
                string indent = "";
                string attributeIndent = "";

                while (xmlReader.Read())
                {
                    if (xmlReader.NodeType == XmlNodeType.Element)
                    {
                        attributeIndent = "";
                        string element = xmlReader.Name;
                        textWriter.Write("{0}<{1}", indent, element);

                        if (!xmlReader.HasAttributes)
                            textWriter.WriteLine(">");
                        else
                        {
                            int actual = 1;
                            while (xmlReader.MoveToNextAttribute())
                            {
                                string content = String.Format("{0} {1}={2}", attributeIndent, xmlReader.Name, xmlReader.Value);
                                if (actual != xmlReader.AttributeCount)
                                    textWriter.WriteLine(content);
                                else
                                    textWriter.Write(content);

                                if (string.IsNullOrEmpty(attributeIndent))
                                    attributeIndent = indent + Enumerable.Repeat<string>(" ", element.Length + 1).Aggregate((a, b) => a + b);

                                actual++;
                            }
                            xmlReader.MoveToElement();
                            textWriter.WriteLine(">");
                            attributeIndent = "";
                        }
                        if (!xmlReader.IsEmptyElement)
                        {
                            indent += "  ";
                            textWriter.WriteLine(">");
                        }
                        else
                            textWriter.WriteLine("/>");
                    }
                    else if (xmlReader.NodeType == XmlNodeType.EndElement)
                    {
                        indent = indent.Substring(0, indent.Length - 2);
                        textWriter.WriteLine("{0}</{1}>", indent, xmlReader.Name);
                    }
                    else if (xmlReader.NodeType == XmlNodeType.Text)
                    {
                        textWriter.WriteLine(xmlReader.Value);
                    }
                }

                return textWriter.ToString();
            }
        }
    }