Creating Custom Configuration Sections in .NET

Every element in the configuration file maps to a class in the .NET framework.  It's possible to expand upon this to create custom configuration sections.  To do this, create a class that inherits from ConfigurationSection, like so:

public class MySection : ConfigurationSection { }

To expose attributes for our new element that can be defined in the configuration file, below is one of the possible syntaxes:

[ConfigurationProperty("defaultValue", IsRequired=true)]
public string DefaultValue
{
    get { return (string)this["defaultValue"]; }
    set { this["defaultValue"] = value; }
}

Let's look at this definition.  First, the ConfigurationProperty attribute exposes this property as an attribute.  There are other optional properties on the attribute that can be setup, such as IsRequired, DefaultValue, IsDefaultCollection, etc.  All of these properties determine how the configuration file will validate the XML.

Next, the property gets and sets value to a local dictionary.  This dictionary is object-based, and will create an entry for your attribute with a default value.  The key has to match the name of the configuration property defined in the attribute.  To make use of this, you must define the following in <configSections> element in the configuration file:

<section name="mySection" type="FullPath.To.MySection,Assembly" />

I can now define the following:

<mySection defaultValue="1" />

And access it using:

MySection section = (MySection)ConfigurationManager.GetSection("mySection");

This call to GetSection returns the instance of the section defined in the configuration file.

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