Creating customisable configuration using .NET

Question

I'm trying to create some typed configuration similar to the following snippet...

<logging application="Global Application Name">
    <defaultLogger name="default" genericOption="XXX" specificOptionYYY="yyy" />
    <defaultLogger name="notAsDefault" genericOption="AAA" specificOptionYYY="bbb" />
    <anotherDefaultLogger name="anotherDefault" genericOption="ZZZ" specificOptionWWW="www" />
</logging>

At the root would be a LoggerSettings class that would contain the application property and a collection of LoggingConfigurationElements.

The LoggingConfigurationElement would contain the genericOption property. There would then be two specific sub-classes that would be created containing the specificOptionYYY and specificOptionWWW.

How would I then go about matching and instantiating the correct sub-class of configuration element at run time based on the element's name?

Answer 1

The trick was to override the OnDeserializeUnrecognizedElement method and dynamically create the configuration element required, and deserialise it manually.

override protected bool OnDeserializeUnrecognizedElement (string elementName, System.Xml.XmlReader 
{
    if (sNames.ContainsKey (elementName))
    {
        var elementType = sNames[elementName];
        if (elementType != null)
        {
            var element = Activator.CreateInstance (elementType) as LoggerConfigurationElement;
            if (element != null)
            {
                element.DeserializeElementForConfig (reader, false);
                BaseAdd (element);
            }
        }

        return true;
    }

    return base.OnDeserializeUnrecognizedElement (elementName, reader);
}

In this example, I've pre-built the list of valid element names using a combination of reflection and configuration (yes, more configuration!) so I know up-front if the supplied element is a valid one.