Simple custom config section with collection in .NET4

Question

I'm trying to write a very simple custom configuration section for a .NET4 application. My goal is this:

<configuration>
  <configSections>
    <section name="myServices" type="My.ConfigSection, My.Assembly" />
  </configSections>
  <myServices>
    <add name="First" />
    <add name="Second" />
  </myServices>
</configuration>

However, I keep getting a ConfigurationErrorsException: 'Unrecognized element 'add'' when I call ConfigurationManager.GetSection("myServices"). I've been staring at it for a while now but haven't figured out yet what I'm doing wrong. Below is my code. It's three classes: ConfigSection, MyServiceSettingsCollection and MyServiceSettings.

First the class that represents the entire config section. It has a nameless default collection of type MyServiceSettingsCollection. The IsDefaultCollection property should allow me to 'add' directly to my collection from the root element.

public sealed class ConfigSection : ConfigurationSection
{
  private static readonly ConfigurationProperty _propMyServices;

  private static readonly ConfigurationPropertyCollection _properties;

  public static ConfigSection Instance { get { return _instance; } }

  static ConfigSection()
  {
    _propMyServices = new ConfigurationProperty(
          null, typeof(MyServiceSettingsCollection), null,
          ConfigurationPropertyOptions.IsDefaultCollection);
    _properties = new ConfigurationPropertyCollection { _propMyServices };
  }

  [ConfigurationProperty("", IsDefaultCollection = true)]
  public MyServiceSettingsCollection MyServices
  {
    get { return (MyServiceSettingsCollection) base[_propMyServices]; }
    set { base[_propMyServices] = value; }
  }

  protected override ConfigurationPropertyCollection Properties
  { get { return _properties; } }
}

Next, the collection class itself. It is of type AddRemoveClearMap.

[ConfigurationCollection(typeof(MyServiceSettings),
    CollectionType = ConfigurationElementCollectionType.AddRemoveClearMap)]
public sealed class MyServiceSettingsCollection : ConfigurationElementCollection
{
  public MyServiceSettings this[int index]
  {
    get { return (MyServiceSettings) BaseGet(index); }
    set
    {
      if (BaseGet(index) != null) { BaseRemoveAt(index); }
      BaseAdd(index, value);
    }
  }

  public new MyServiceSettings this[string key]
  {
    get { return (MyServiceSettings) BaseGet(key); }
  }

  protected override ConfigurationElement CreateNewElement()
  {
    return new MyServiceSettings();
  }

  protected override object GetElementKey(ConfigurationElement element)
  {
    return ((MyServiceSettings) element).Key;
  }
}

And finally a class for the elements in the collection. For now, this class has one property but there will be more later (which prevents me from using NameValueSectionHandler).

public class MyServiceSettings : ConfigurationElement
{
  private static readonly ConfigurationProperty _propName;

  private static readonly ConfigurationPropertyCollection properties;

  static MyServiceSettings()
  {
    _propName = new ConfigurationProperty("name", typeof(string), null, null,
                                          new StringValidator(1),
                                          ConfigurationPropertyOptions.IsRequired |
                                          ConfigurationPropertyOptions.IsKey);
    properties = new ConfigurationPropertyCollection { _propName };
  }

  [ConfigurationProperty("name", DefaultValue = "",
        Options = ConfigurationPropertyOptions.IsRequired |
                  ConfigurationPropertyOptions.IsKey)]
  public string Name
  {
      get { return (string) base[_propKey]; }
      set { base[_propKey] = value; }
  }

  protected override ConfigurationPropertyCollection Properties
  { get { return properties; } }
}

Answer 1

Ok, I found the seemingly random fix. Instead of this:

[ConfigurationProperty("", IsDefaultCollection = true)]
public ProvisiorServiceSettingsCollection ProvisiorServices
{ ... }

you should use:

[ConfigurationProperty("", Options = ConfigurationPropertyOptions.IsDefaultCollection)]
public ProvisiorServiceSettingsCollection ProvisiorServices
{ ... }

No idea what the difference is between the two. To me, they look strikingly similar... or at least, there is no suggestion anywhere why one is preferred over the other.

Answer 2

Since I spent a good amount of time on this, thought I'd add a real world example I just implemented in this commit: https://github.com/rhythmagency/formulate/commit/4d2a95e1a82eb6b3500ab0869b8f8b15bd3deaa9

Here was my goal for my web.config (which I was able to achieve):

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <configSections>
    <sectionGroup name="formulateConfiguration">
      <section name="templates" type="formulate.app.Configuration.TemplatesConfigSection, formulate.app" requirePermission="false"/>
    </sectionGroup>
  </configSections>
  <formulateConfiguration>
    <templates>
      <template name="Responsive" path="~/Views/Formulate/Responsive.Bootstrap.Angular.cshtml" />
    </templates>
  </formulateConfiguration>
</configuration>

This is the class for the highest-level "templates" configuration section:

namespace formulate.app.Configuration
{

    // Namespaces.
    using System.Configuration;


    /// <summary>
    /// A configuration section for Formulate templates.
    /// </summary>
    public class TemplatesConfigSection : ConfigurationSection
    {

        #region Properties

        /// <summary>
        /// The templates in this configuration section.
        /// </summary>
        [ConfigurationProperty("", IsDefaultCollection = true)]
        [ConfigurationCollection(typeof(TemplateCollection), AddItemName = "template")]
        public TemplateCollection Templates
        {
            get
            {
                return base[""] as TemplateCollection;
            }
        }

        #endregion

    }

}

Here's the next level down, the collection class:

namespace formulate.app.Configuration
{

    // Namespaces.
    using System.Configuration;


    /// <summary>
    /// A collection of templates from the configuration.
    /// </summary>
    [ConfigurationCollection(typeof(TemplateElement))]
    public class TemplateCollection : ConfigurationElementCollection
    {

        #region Methods

        /// <summary>
        /// Creates a new template element.
        /// </summary>
        /// <returns>The template element.</returns>
        protected override ConfigurationElement CreateNewElement()
        {
            return new TemplateElement();
        }


        /// <summary>
        /// Gets the key for an element.
        /// </summary>
        /// <param name="element">The element.</param>
        /// <returns>The key.</returns>
        protected override object GetElementKey(ConfigurationElement element)
        {
            return (element as TemplateElement).Name;
        }

        #endregion

    }

}

And here's the deepest level class (the individual templates):

namespace formulate.app.Configuration
{

    //  Namespaces.
    using System.Configuration;


    /// <summary>
    /// A "template" configuration element.
    /// </summary>
    public class TemplateElement : ConfigurationElement
    {

        #region Constants

        private const string DefaultPath = "~/*Replace Me*.cshtml";

        #endregion


        #region Properties

        /// <summary>
        /// The name of the template.
        /// </summary>
        [ConfigurationProperty("name", IsRequired = true)]
        public string Name
        {
            get
            {
                return base["name"] as string;
            }
            set
            {
                this["name"] = value;
            }
        }


        /// <summary>
        /// The path to this template.
        /// </summary>
        /// <remarks>
        /// Should start with "~" and end with ".cshtml".
        /// </remarks>
        [ConfigurationProperty("path", IsRequired = true, DefaultValue = DefaultPath)]
        [RegexStringValidator(@"^~.*\.[cC][sS][hH][tT][mM][lL]$")]
        public string Path
        {
            get
            {
                var result = base["path"] as string;
                return result == DefaultPath ? null : result;
            }
            set
            {
                this["path"] = value;
            }
        }

        #endregion

    }

}

The important bit for me was to have the empty string in the ConfigurationPropertyAttribute and setting IsDefaultCollection to true. By the way, I put my config in an external file that looks like this:

<?xml version="1.0" encoding="utf-8" ?>
<templates>
    <template name="Responsive" path="~/Views/Formulate/Responsive.Bootstrap.Angular.cshtml" />
</templates>

And in that case, my web.config looks like this:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <configSections>
    <sectionGroup name="formulateConfiguration">
      <section name="templates" type="formulate.app.Configuration.TemplatesConfigSection, formulate.app" requirePermission="false"/>
    </sectionGroup>
  </configSections>
  <formulateConfiguration>
    <templates configSource="config\Formulate\templates.config"/>
  </formulateConfiguration>
</configuration>

Figured I'd mention that in case somebody else is trying to add it to an external file (it's somewhat non-intuitive that the root-level item in the external file is the same as the externalized element from the web.config).

Answer 3

it seems you are missing something similar to this

[ConfigurationProperty("urls", IsDefaultCollection = false)]
    [ConfigurationCollection(typeof(UrlsCollection),
        AddItemName = "add",
        ClearItemsName = "clear",
        RemoveItemName = "remove")]

for more information see http://msdn.microsoft.com/en-us/library/system.configuration.configurationcollectionattribute.aspx