Create Custom Configuration Config Section in Web.Config/ App.Config

Suppose i have explained example with Browser Compatibility Configuration with Custom config section.

Register Configuration Class into Config Section in Config File.

<configSections>
    <section name="BrowserConfiguration" type="Demo.Web.BrowserConfiguration, Demo" allowDefinition="Everywhere" allowLocation="true"/>
 </configSections>

Add Your Configuration below Config Section Tag into Web.Config/App.Config

<BrowserConfiguration>
    <platforms>
      <platform name="winnt">
        <browsers>
          <browser browsername="IE" version="10"></browser>
          <browser browsername="FIREFOX" version="9"></browser>
          <browser browsername="CHROME" version="25"></browser>
        </browsers>
      </platform>
      <platform name="mac">
        <browsers>
          <browser browsername="IE" version="8"></browser>
          <browser browsername="CHROME" version="20"></browser>
        </browsers>
      </platform>
      <platform name="mobile">
        <browsers>
          <browser browsername="IE" version="4"></browser>
          <browser browsername="CHROME" version="10"></browser>
        </browsers>
      </platform>
    </platforms>
  </BrowserConfiguration>

Create Class For Configuration as Below.



public class BrowserElement : ConfigurationElement
{
    [ConfigurationProperty("browsername", IsRequired = true, IsKey = true)]
    public string BrowserName
    {
        get
        {
            return this["browsername"] as string;
        }
    }


    [ConfigurationProperty("version", IsRequired = true, DefaultValue = 1.0)]
    public double Version
    {
        get
        {
            return Convert.ToDouble(this["version"]);
        }
    }
}

public class BrowserCollection : ConfigurationElementCollection
{
    public new BrowserElement this[string name]
    {
        get
        {
            if (IndexOf(name) < 0)
                return null;

            return (BrowserElement)BaseGet(name);
        }
    }

    public BrowserElement this[int index]
    {
        get
        {
            return (BrowserElement)BaseGet(index);
        }
    }


    public int IndexOf(string name)
    {
        for (int idx = 0; idx < base.Count; idx++)
        {
            if (this[idx].BrowserName.Equals(name, StringComparison.CurrentCultureIgnoreCase))
                return idx;
        }

        return -1;
    }

    public int IndexOf(BrowserElement browser)
    {
        return BaseIndexOf(browser);
    }


    public override ConfigurationElementCollectionType CollectionType
    {
        get { return ConfigurationElementCollectionType.BasicMap; }
    }

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

    protected override object GetElementKey(ConfigurationElement element)
    {
        return ((BrowserElement)element).BrowserName;
    }

    protected override string ElementName
    {
        get { return "browser"; }
    }
}

public class PlatformElement : ConfigurationElement
{
    private string m_platform = "winnt";

    [ConfigurationProperty("name", IsKey = true, IsRequired = true)]
    public string Name
    {
        get
        {
            return Convert.ToString(base["name"]);
        }
    }

    [ConfigurationProperty("browsers", IsDefaultCollection = false)]
    public BrowserCollection Browsers
    {
        get
        {
            return (BrowserCollection)base["browsers"];
        }
    }
}

public class PlatformCollection : ConfigurationElementCollection
{
    new public PlatformElement this[string name]
    {
        get
        {
            if (IndexOf(name) < 0)
                return null;

            return (PlatformElement)BaseGet(name);
        }
    }

    public PlatformElement this[int index]
    {
        get
        {
            return (PlatformElement)BaseGet(index);
        }
        set
        {
            if (BaseGet(index) != null)
            {
                BaseRemoveAt(index);
            }

            BaseAdd(index, value);
        }
    }


    public int IndexOf(string name)
    {
        for (int idx = 0; idx < base.Count; idx++)
        {
            if (this[idx].Name.Trim().Equals(name, StringComparison.CurrentCultureIgnoreCase))
                return idx;
        }

        return -1;
    }

    public int IndexOf(PlatformElement platform)
    {
        return BaseIndexOf(platform);
    }


    public override ConfigurationElementCollectionType CollectionType
    {
        get
        {
            return ConfigurationElementCollectionType.BasicMap;
        }
    }

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

    protected override Object GetElementKey(ConfigurationElement element)
    {
        return ((PlatformElement)element).Name;
    }


    public void Add(PlatformElement platform)
    {
        BaseAdd(platform);
    }

    protected override void BaseAdd(ConfigurationElement element)
    {
        BaseAdd(element, false);
    }

    public void Remove(PlatformElement platform)
    {
        if (BaseIndexOf(platform) >= 0)
            BaseRemove(platform.Name);
    }

    public void RemoveAt(int index)
    {
        BaseRemoveAt(index);
    }

    public void Remove(string name)
    {
        BaseRemove(name);
    }

    public void Clear()
    {
        BaseClear();
    }

    protected override string ElementName
    {
        get { return "platform"; }
    }
}

public class BrowserConfiguration : ConfigurationSection
{
    private static string m_ConfigurationSectionConst = "BrowserConfiguration";

    public static BrowserConfiguration GetConfig()
    {
        return (BrowserConfiguration)ConfigurationManager.GetSection(BrowserConfiguration.m_ConfigurationSectionConst) ?? new BrowserConfiguration();
    }


    [ConfigurationCollection(typeof(PlatformCollection), AddItemName = "platform")]
    [ConfigurationProperty("platforms", IsDefaultCollection = true)]
    public PlatformCollection Platforms
    {
        get
        {
            return (PlatformCollection)this["platforms"] ?? new PlatformCollection();
        }
    }
}

To read Config Section Configuration into Code , Write below Code 

var collection = BrowserConfiguration.GetConfig();

PlatformCollection values = collection.Platforms;

int index = values.IndexOf(Request.Browser.Platform);

if (index >= 0)

{

    PlatformElement platform = values[index];

    int browserindex = platform.Browsers.IndexOf(Request.Browser.Browser);

    if (browserindex >= 0)

    {

        BrowserElement browser = platform.Browsers[browserindex];

        if (browser.Version > (Convert.ToDouble(Request.Browser.MajorVersion) + Request.Browser.MinorVersion))

        {

            Server.Transfer("BrowserCompatible.aspx", false);

        }

    }

}