string escape into XML-Attribute

I had a look at string escape into XML and found it very useful.

I would like to do a similar thing: Escape a string to be used in an XML-Attribute.

The string may contain \r\n. The XmlWriter class produces something like \r\n -> 


The solution I'm currently using includes the XmlWriter and a StringBuilder and is rather ugly.

Any hints?

Edit1:
Sorry to disappoint LarsH, buy my first approach was

public static string XmlEscapeAttribute(string unescaped)
{
    XmlDocument doc = new XmlDocument();
    XmlAttribute attr= doc.CreateAttribute("attr");
    attr.InnerText = unescaped;
    return attr.InnerXml;
}

It does not work. XmlEscapeAttribute("Foo\r\nBar") will result in "Foo\r\nBar"

I used the .NET Reflector, to find out how the XmlTextWriter escapes Attributes. It uses the XmlTextEncoder class which is internal...

My method I'm currently usig lokks like this:

public static string XmlEscapeAttribute(string unescaped)
{
    if (String.IsNullOrEmpty(unescaped)) return unescaped;

    XmlWriterSettings settings = new XmlWriterSettings();
    settings.OmitXmlDeclaration = true;
    StringBuilder sb = new StringBuilder();
    XmlWriter writer = XmlWriter.Create(sb, settings);

    writer.WriteStartElement("a");
    writer.WriteAttributeString("a", unescaped);
    writer.WriteEndElement();
    writer.Flush();
    sb.Length -= "\" />".Length;
    sb.Remove(0, "<a a=\"".Length);

    return sb.ToString();
}

It's ugly and probably slow, but it does work: XmlEscapeAttribute("Foo\r\nBar") will result in "Foo
Bar"

Edit2:

SecurityElement.Escape(unescaped);

does not work either.

Edit3 (final)