How to have a collection of configuration sections in a .config file

Question

I want to be able to use the following setup in my app/web.config files:

<listeners>
    <listener type="a">
         <parameter name="a", value="2" />
         <parameter name="b", value="20" />
    </listener>
    <listener type="b">
         <parameter name="a", value="2" />
         <parameter name="b", value="20" />
         <parameter name="c", value="200" />
    </listener>
    ...
</listeners>

Basically, I want to represent a collection of listeners, where each listener has several attributes as well as a collection of parameters. I've managed to model the listener element as a ConfigurationSection with the parameters as ConfigurationElements. However, I can't find an example of how to create the outer collection of listeners. What do I need to do to model this?

I tried making listeners a ConfigurationSectionGroup but this failed at runtime because it seems like the group can't have multiple sections of the same name.

Answer 1

It might be a cop-out since this doesn't use any custom handlers, but you could use an arbitrary XML section in conjunction with an XmlSerializer.

  <section name="listeners" type="System.Configuration.DefaultSection" />
  ...

<listeners>
  <listener type="a">
    <parameter name="a" value="2" />
    <parameter name="b" value="20" />
  </listener>
  <listener type="a">
    <parameter name="a" value="2" />
    <parameter name="b" value="20" />
    <parameter name="c" value="200" />
  </listener>
</listeners>

To obtain the array of listeners, get the raw XML and deserialize it if you want objects.

The serializable classes:

public class Parameter
{
    [XmlAttribute("name")]
    public String Name { get; set; }
    [XmlAttribute("value")]
    public Int32 Value { get; set; }
}

[XmlType(TypeName = "listener")]
public class Listener
{
    [XmlAttribute("type")]
    public String Type { get; set; }

    [XmlElement("parameter")]
    public Parameter[] Parameters;
}

And, the operation itself:

var serializer = new XmlSerializer(typeof(Listener[]), 
                                   new XmlRootAttribute("listeners"));
var configuration = ConfigurationManager
    .OpenExeConfiguration(ConfigurationUserLevel.None);
var section = configuration.GetSection("listeners");
var rawXml = section.SectionInformation.GetRawXml();
using (var stringReader = new StringReader(rawXml))
{
    var listeners = (Listener[])serializer.Deserialize(stringReader);
}

(Or, instead of XmlSerializer, you could use XDocument to parse the XML and peek at individual elements or attributes.)