Custom attribute in App.config

This article I have mostly copy / pasted from here.

Here I've already explained how to create custom section in App.config, but now I need more complicated stuff, I need to have more attributes then just key / value pair.

Here is the example:

using System;
using System.Collections.Specialized;
using System.Configuration;

namespace CustomConfig
{
  class Program
  {
    static void Main(string[] args)
    {
      MilosevBlogConfig links = (MilosevBlogConfig)ConfigurationManager.GetSection("milosev.com");
      string homePage = ConfigurationManager.AppSettings.Get("homePage");

      Console.WriteLine("Home page: " + homePage);

      foreach (MilosevBlogCategoriesElement link in links.MilosevBlogInstances)
      {
        Console.WriteLine("Blog category: " + link.BlogCategory);
      }

      Console.WriteLine("Press any key...");
      Console.ReadKey();
    }
  }

  public class MilosevBlogCategoriesElement : ConfigurationElement
  {
    [ConfigurationProperty("BlogCategory", IsKey = true, IsRequired = true)]
    public string BlogCategory
    {
      get
      {
        return (string)base["BlogCategory"];
      }
      set
      {
        base["BlogCategory"] = value;
      }
    }
  }

  public class MilosevBlogCategoriesElementCollection : ConfigurationElementCollection
  {
    public MilosevBlogCategoriesElement this[int index]
    {
      get
      {

        return (MilosevBlogCategoriesElement)BaseGet(index);
      }
      set
      {
        if (BaseGet(index) != null)
          BaseRemoveAt(index);

        BaseAdd(index, value);
      }
    }

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

    protected override object GetElementKey(ConfigurationElement element)
    {
      return ((MilosevBlogCategoriesElement)element).BlogCategory;
    }
  }

  public class MilosevBlogConfig : ConfigurationSection
  {
    [ConfigurationProperty("categories")]
    [ConfigurationCollection(typeof(MilosevBlogCategoriesElementCollection))]
    public MilosevBlogCategoriesElementCollection MilosevBlogInstances
    {
      get
      {
        return (MilosevBlogCategoriesElementCollection)this["categories"];
      }
    }
  }
}

App.config should look like this:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>

  <configSections>
    <section name="milosev.com" type="CustomConfig.MilosevBlogConfig, CustomConfig"></section>
  </configSections>

  <milosev.com>
    <categories>
      <add BlogCategory="csharp"/>
      <add BlogCategory="asp.net MVC"/>
    </categories>
  </milosev.com>

  <appSettings>
    <add key="homePage" value="http://milosev.com/" />
  </appSettings>

  <startup>
    <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.6.1" />
  </startup>
</configuration>

POI in App.config:

  <configSections>
    <section name="milosev.com" type="CustomConfig.MilosevBlogConfig, CustomConfig"></section>
  </configSections>

Where MilosevBlogConfig looks like:

public class MilosevBlogConfig : ConfigurationSection
{
  [ConfigurationProperty("categories")]
  [ConfigurationCollection(typeof(MilosevBlogCategoriesElementCollection))]
  public MilosevBlogCategoriesElementCollection MilosevBlogInstances
  {
    get
    {
      return (MilosevBlogCategoriesElementCollection)this["categories"];
    }
  }
}

Source code you can download from here.