James Sperring

I'm sure this should be easy, but it's taken me most of a morning of reading MSDN and tweaking code to get it to work. Most of the documentation that I have found has either been massively out of context, showing small segments of code and not explaining where it fits in or what it does; or it's been hugely over complicated, showing complete examples with masses of boilerplate code.

I've been trying to get a simple collection, using <AddElement> tags to add a list of items, similar to how AppSettings and ConnectionStrings sections work. It was extremely easy to create a custom configuration section, with a single item and associated properties - creating a collection of items, with add/remove/clear functionality appeared to be a different matter.

Turns out, it's actually not that difficult. 3 classes, 2 overrides, and some properties. After that, it's just a case of registering the custom section in the configuration file in the <configSections> section.

Section class

The section class inherits from ConfigurationSection, and serves as the wrapper for your configuration section in the app.config file. This is what you'll add to the <configSections> attribute to register the type in the Configuration manager:

public class ElementSection : ConfigurationSection
{
    [ConfigurationProperty("Elements", IsDefaultCollection = false)]
    [ConfigurationCollection(typeof(Elements), AddItemName = "AddElement", ClearItemsName = "ClearElements", RemoveItemName = "RemoveElement")]
    public Elements Elements
    { get { return this["Elements"] as Elements; } }
}

Collection class

The collection class is required to tell the Configuration manager what to create and what to use to retrieve the elements. There are 2 required overrides for this class:

public class Elements : ConfigurationElementCollection
{
    protected override ConfigurationElement CreateNewElement()
    {
        return new Element();
    }

    protected override object GetElementKey(ConfigurationElement element)
    {
        return (element as Element).Name;
    }
}

Element class

The class that contains your actual elements, all that's required here is a property for each value you want to store against the element, which needs to be decorated with the ConfigurationProperty attribute.

public class Element : ConfigurationElement
{
    [ConfigurationProperty("Name", IsRequired = true)]
    public string Name
    { 
        get { return (string) this["Name"]; } 
        set { this["Name"] = value; }
    }
}

app.config registration

The app.config file registration should be fairly trivial, all that's required is the name you want to give the section, the namespace and class name, and the assembly name:

<configuration>
    <configSections>
        <section name="ElementSection"
                     type="namespace.ElementSection, AssemblyName />
    </configSections>
</configuration> 

And that's all there is to it. If anything is not clear, drop a comment and I'll try to clarify.