How to return an XML string as an action result in MVC [duplicate]

You could use return this.Content(xmlString, "text/xml"); to return a built XML string from an action.

For JSON/XML I have written an XML/JSON Action Filter that makes it very easy to tackle without handling special cases in your action handler (which is what you seem to be doing).

Another way to do this is by using XDocument:

using System.Xml.Linq;

public XDocument ExportXml()
{
    Response.AddHeader("Content-Type", "text/xml");

    return XDocument.Parse("<xml>...");
}

If you're building the XML using Linq-to-XML then check out my answer here. It allows you to write code like this:

public ActionResult MyXmlAction()
{
    var xml = new XDocument(
        new XElement("root",
            new XAttribute("version", "2.0"),
            new XElement("child", "Hello World!")));

    return new XmlActionResult(xml);
}