<configuration>
  <configSections>
    <section name="MyUrls" type="Samples.AspNet.UrlsSection, ConfigurationCollectionAttribute" />
  </configSections>
  <MyUrls>
    <urls>
      <clear />
      <add name="Microsoft" url="http://www.microsoft.com" port="0" />
      <add name="Contoso" url="http://contoso.com" port="1" />
    </urls>
  </MyUrls>
</configuration>

' Set assembly name to "ConfigurationCollectionAttribute", 
' and set root namespace to "Samples.AspNet" to match the
' section declaration in the sample app.config file.
' Set startup object to "TestingConfigurationCollectionAttribute".
Imports System
Imports System.Configuration

Class TestingConfigurationCollectionAttribute

    Shared Sub Main()
        ' Call ConfigurationManager to read the custom UrlsSection
        ' of the app.config file and put its contents into an 
        ' instance of the custom class created for it.
        Dim myUrlsSection As UrlsSection = _
            ConfigurationManager.GetSection("MyUrls")

        If myUrlsSection Is Nothing Then
            Console.WriteLine("Failed to load UrlsSection.")
        Else
            Console.WriteLine("URLS defined in app.config:")
            Dim i As Integer
            For i = 0 To myUrlsSection.Urls.Count - 1
                Console.WriteLine("  Name={0} URL={1} Port={2}", _
                myUrlsSection.Urls(i).Name, _
                myUrlsSection.Urls(i).Url, _
                myUrlsSection.Urls(i).Port)
            Next i
        End If
        Console.ReadLine()
    End Sub 'Main

End Class

' Define a custom section named UrlsSection containing a
' UrlsCollection collection of UrlConfigElement elements.
' The collection is wrapped in an element named "urls" in the
' app.config file.
' UrlsCollection and UrlsConfigElement classes are defined below.
Public Class UrlsSection
    Inherits ConfigurationSection

    ' Declare the urls collection property.
    ' Note: the "IsDefaultCollection = false" instructs 
    '.NET Framework to build a nested section of 
    'the kind <urls> ...</urls>.
    <ConfigurationProperty("urls", _
        IsDefaultCollection:=False), _
        ConfigurationCollection(GetType(UrlsCollection), _
        AddItemName:="add", _
        ClearItemsName:="clear", _
        RemoveItemName:="remove")> _
    Public ReadOnly Property Urls() As UrlsCollection
        Get
            Dim urlCollection As UrlsCollection = _
            CType(MyBase.Item("urls"), UrlsCollection)
            Return urlCollection
        End Get
    End Property

End Class 'UrlsSection 

' Define the UrlsCollection that will contain the 
' UrlsConfigElement elements.
Public Class UrlsCollection
    Inherits ConfigurationElementCollection

    Public Sub New()
        ' When the collection is created, always add one element 
        ' with the default values. (This is not necessary; it is
        ' here only to illustrate what can be done; you could 
        ' also create additional elements with other hard-coded 
        ' values here.)
        Dim url As UrlConfigElement = _
        CType(CreateNewElement(), UrlConfigElement)
        Add(url)
    End Sub 'New

    Public Overrides ReadOnly Property CollectionType() _
    As ConfigurationElementCollectionType
        Get
            Return ConfigurationElementCollectionType.AddRemoveClearMap
        End Get
    End Property

    Protected Overrides Function CreateNewElement() _
    As ConfigurationElement
        Return New UrlConfigElement()
    End Function 'CreateNewElement

    Protected Overrides Function GetElementKey(ByVal element _
    As ConfigurationElement) As [Object]
        Return CType(element, UrlConfigElement).Name
    End Function 'GetElementKey

    Default Public Shadows Property Item( _
    ByVal index As Integer) As UrlConfigElement
        Get
            Return CType(BaseGet(index), UrlConfigElement)
        End Get
        Set(ByVal value As UrlConfigElement)
            If Not (BaseGet(index) Is Nothing) Then
                BaseRemoveAt(index)
            End If
            BaseAdd(index, value)
        End Set
    End Property

    Default Public Shadows ReadOnly Property Item( _
    ByVal Name As String) As UrlConfigElement
        Get
            Return CType(BaseGet(Name), UrlConfigElement)
        End Get
    End Property

    Public Function IndexOf(ByVal url _
    As UrlConfigElement) As Integer
        Return BaseIndexOf(url)
    End Function 'IndexOf

    Public Sub Add(ByVal url As UrlConfigElement)
        BaseAdd(url)
    End Sub 'Add

    Protected Overrides Sub BaseAdd(ByVal element _
    As ConfigurationElement)
        BaseAdd(element, False)
    End Sub 'BaseAdd

    Public Overloads Sub Remove(ByVal url _
    As UrlConfigElement)
        If BaseIndexOf(url) >= 0 Then
            BaseRemove(url.Name)
        End If
    End Sub 'Remove

    Public Sub RemoveAt(ByVal index As Integer)
        BaseRemoveAt(index)
    End Sub 'RemoveAt

    Public Overloads Sub Remove(ByVal name As String)
        BaseRemove(name)
    End Sub 'Remove

    Public Sub Clear()
        BaseClear()
    End Sub 'Clear
End Class 'UrlsCollection 

' Define the element type contained by the UrlsCollection
' collection.
Public Class UrlConfigElement
    Inherits ConfigurationElement

    Public Sub New(ByVal name As String, ByVal url As String)
        Me.Name = name
        Me.Url = url
    End Sub 'New

    Public Sub New()
    End Sub

    <ConfigurationProperty("name", _
    DefaultValue:="Microsoft", _
    IsRequired:=True, _
    IsKey:=True)> _
    Public Property Name() As String
        Get
            Return CStr(Me("name"))
        End Get
        Set(ByVal value As String)
            Me("name") = value
        End Set
    End Property

    <ConfigurationProperty("url", _
    DefaultValue:="http://www.microsoft.com", _
    IsRequired:=True), _
    RegexStringValidator("\w+:\/\/[\w.]+\S*")> _
    Public Property Url() As String
        Get
            Return CStr(Me("url"))
        End Get
        Set(ByVal value As String)
            Me("url") = value
        End Set
    End Property

    <ConfigurationProperty("port", _
    DefaultValue:=0, IsRequired:=False), _
    IntegerValidator(MinValue:=0, _
    MaxValue:=8080, ExcludeRange:=False)> _
   Public Property Port() As Integer
        Get
            Return CInt(Me("port"))
        End Get
        Set(ByVal value As Integer)
            Me("port") = value
        End Set
    End Property
End Class 'UrlConfigElement 

// Set assembly name to "ConfigurationCollectionAttribute" to match
// the section declaration in the sample app.config file.
using System;
using System.Configuration;


namespace Samples.AspNet
{
    class TestingConfigurationCollectionAttribute
    {
        static void Main(string[] args)
        {
            // Call ConfigurationManager to read the custom UrlsSection
            // of the app.config file and put its contents into an 
            // instance of the custom class created for it.
            UrlsSection myUrlsSection =
               ConfigurationManager.GetSection("MyUrls") as UrlsSection;

            if (myUrlsSection == null)
                Console.WriteLine("Failed to load UrlsSection.");
            else
            {
                Console.WriteLine("URLs defined in app.config:");
                for (int i = 0; i < myUrlsSection.Urls.Count; i++)
                {
                    Console.WriteLine("  Name={0} URL={1} Port={2}",
                        myUrlsSection.Urls[i].Name,
                        myUrlsSection.Urls[i].Url,
                        myUrlsSection.Urls[i].Port);
                }
            }
            Console.ReadLine();
        }
    }

    // Define a custom section named UrlsSection containing a
    // UrlsCollection collection of UrlConfigElement elements.
    // The collection is wrapped in an element named "urls" in the
    // app.config file.
    // UrlsCollection and UrlsConfigElement classes are defined below.
    public class UrlsSection : ConfigurationSection
    {
        // Declare the urls collection property.
        // Note: the "IsDefaultCollection = false" instructs 
        // .NET Framework to build a nested section of 
        // the kind <urls>...</urls>.
        [ConfigurationProperty("urls", IsDefaultCollection = false)]
        [ConfigurationCollection(typeof(UrlsCollection),
            AddItemName = "add",
            ClearItemsName = "clear",
            RemoveItemName = "remove")]
        public UrlsCollection Urls
        {
            get
            {
                UrlsCollection urlsCollection = 
                    (UrlsCollection)base["urls"];
                return urlsCollection;
            }
        }

    }

    // Define the UrlsCollection that will contain the UrlsConfigElement
    // elements.
    public class UrlsCollection : ConfigurationElementCollection
    {
        public UrlsCollection()
        {
            // When the collection is created, always add one element 
            // with the default values. (This is not necessary; it is
            // here only to illustrate what can be done; you could 
            // also create additional elements with other hard-coded 
            // values here.)
            UrlConfigElement url = (UrlConfigElement)CreateNewElement();
            Add(url);
        }

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

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

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

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

        new public UrlConfigElement this[string Name]
        {
            get
            {
                return (UrlConfigElement)BaseGet(Name);
            }
        }

        public int IndexOf(UrlConfigElement url)
        {
            return BaseIndexOf(url);
        }

        public void Add(UrlConfigElement url)
        {
            BaseAdd(url);
        }
        protected override void BaseAdd(ConfigurationElement element)
        {
            BaseAdd(element, false);
        }

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

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

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

        public void Clear()
        {
            BaseClear();
        }
    }

    // Define the element type contained by the UrlsCollection
    // collection.
    public class UrlConfigElement : ConfigurationElement
    {
        public UrlConfigElement(String name, String url)
        {
            this.Name = name;
            this.Url = url;
        }

        public UrlConfigElement()
        {
            // Attributes on the properties provide default values.
        }

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

        [ConfigurationProperty("url", DefaultValue = "http://www.microsoft.com",
            IsRequired = true)]
        [RegexStringValidator(@"\w+:\/\/[\w.]+\S*")]
        public string Url
        {
            get
            {
                return (string)this["url"];
            }
            set
            {
                this["url"] = value;
            }
        }

        [ConfigurationProperty("port", DefaultValue = (int)0, IsRequired = false)]
        [IntegerValidator(MinValue = 0, MaxValue = 8080, ExcludeRange = false)]
        public int Port
        {
            get
            {
                return (int)this["port"];
            }
            set
            {
                this["port"] = value;
            }
        }
    }
}