ConfigurationElement Class

Definition

public ref class ConfigurationElement abstract

public abstract class ConfigurationElement

type ConfigurationElement = class

Public MustInherit Class ConfigurationElement

Inheritance

Object

ConfigurationElement

Derived

System.Configuration.ConfigurationBuilderSettings

System.Configuration.ConfigurationElementCollection

System.Configuration.ConfigurationSection

System.Configuration.ConnectionStringSettings

System.Configuration.IdnElement

More…

Examples

The following code example shows how to implement a custom ConfigurationElement both as an individual element in a custom section and as a collection of elements in a custom section. The example consists of the following files:

• An app.config file that contains a custom section that is named MyUrls. This section contains a simple element (it does not contain any other elements) and a collection of elements. The simple element is named simple and the collection is named urls.

• A console application. The application reads the contents of the app.config file and writes the information to the console. It uses classes that derive from ConfigurationElement, ConfigurationElementCollection, and ConfigurationSection.

• A class named UrlsSection that derives from the ConfigurationSection class. This class is used to access the MyUrls section in the configuration file.

• A class named UrlsCollection that derives from the ConfigurationElementCollection class. This class is used to access the urls collection in the configuration file.

• A class named UrlConfigElement that derives from the ConfigurationElement class. This class is used to access the simple element and the members of the urls collection in the configuration file.

To run the example, perform the following steps:

1. Create a solution that has a console application project and a class library project that is named ConfigurationElement.

2. Put the three class files in the class library project and put the other files in the console library project.

3. In both projects set a reference to System.Configuration.

4. In the console application project set a project reference to the class library project.

// Set Assembly name to ConfigurationElement
using System;
using System.Configuration;
using System.Collections;

namespace Samples.AspNet
{
    // Entry point for console application that reads the 
    // app.config file and writes to the console the 
    // URLs in the custom section.  
    class TestConfigurationElement
    {
        static void Main(string[] args)
        {
            // Get current configuration file.
            System.Configuration.Configuration config =
                ConfigurationManager.OpenExeConfiguration(
                ConfigurationUserLevel.None);

            // Get the MyUrls section.
            UrlsSection myUrlsSection =
                config.GetSection("MyUrls") as UrlsSection;

            if (myUrlsSection == null)
            {
                Console.WriteLine("Failed to load UrlsSection.");
            }
            else
            {
                Console.WriteLine("The 'simple' element of app.config:");
                Console.WriteLine("  Name={0} URL={1} Port={2}",
                    myUrlsSection.Simple.Name,
                    myUrlsSection.Simple.Url,
                    myUrlsSection.Simple.Port);

                Console.WriteLine("The urls collection of 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();
        }
    }
}

' Set Assembly name to ConfigurationElement
' and set Root namespace to Samples.AspNet
Imports System.Configuration
Imports System.Collections

Class TestConfigurationElement
    ' Entry point for console application that reads the 
    ' app.config file and writes to the console the 
    ' URLs in the custom section.
    Shared Sub Main(ByVal args() As String)
        ' Get the current configuration file.
        Dim config As System.Configuration.Configuration = _
            ConfigurationManager.OpenExeConfiguration( _
            ConfigurationUserLevel.None)

        ' Get the MyUrls section.
        Dim myUrlsSection As UrlsSection = _
            config.GetSection("MyUrls")

        If myUrlsSection Is Nothing Then
            Console.WriteLine("Failed to load UrlsSection.")
        Else
            Console.WriteLine("The 'simple' element of app.config:")
            Console.WriteLine("  Name={0} URL={1} Port={2}", _
                myUrlsSection.Simple.Name, _
                myUrlsSection.Simple.Url, _
                myUrlsSection.Simple.Port)
            Console.WriteLine("The urls collection of app.config:")
            Dim i As Integer
            For i = 0 To myUrlsSection.Urls.Count - 1
                Console.WriteLine("  Name={0} URL={1} Port={2}", _
                i, myUrlsSection.Urls(i).Name, _
                myUrlsSection.Urls(i).Url, _
                myUrlsSection.Urls(i).Port)
            Next i
        End If
        Console.ReadLine()
    End Sub
End Class

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

namespace Samples.AspNet
{
    // Define a custom section containing an individual
    // element and a collection of elements.
    public class UrlsSection : ConfigurationSection
    {
        [ConfigurationProperty("name", 
            DefaultValue = "MyFavorites",
            IsRequired = true, 
            IsKey = false)]
        [StringValidator(InvalidCharacters = 
            " ~!@#$%^&*()[]{}/;'\"|\\",
            MinLength = 1, MaxLength = 60)]
        public string Name
        {

            get
            {
                return (string)this["name"];
            }
            set
            {
                this["name"] = value;
            }
        }

        // Declare an element (not in a collection) of the type
        // UrlConfigElement. In the configuration
        // file it corresponds to <simple .... />.
        [ConfigurationProperty("simple")]
        public UrlConfigElement Simple
        {
            get
            {
                UrlConfigElement url =
                (UrlConfigElement)base["simple"];
                return url;
            }
        }

        // Declare a collection element represented 
        // in the configuration file by the sub-section
        // <urls> <add .../> </urls> 
        // Note: the "IsDefaultCollection = false" 
        // instructs the .NET Framework to build a nested 
        // section like <urls> ...</urls>.
        [ConfigurationProperty("urls",
            IsDefaultCollection = false)]
        public UrlsCollection Urls
        {
            get
            {
                UrlsCollection urlsCollection =
                (UrlsCollection)base["urls"];
                return urlsCollection;
            }
        }

        protected override void DeserializeSection(
            System.Xml.XmlReader reader)
        {
            base.DeserializeSection(reader);
            // You can add custom processing code here.
        }

        protected override string SerializeSection(
            ConfigurationElement parentElement,
            string name, ConfigurationSaveMode saveMode)
        {
            string s =
                base.SerializeSection(parentElement,
                name, saveMode);
            // You can add custom processing code here.
            return s;
        }
    }
}

Imports System.Configuration
Imports System.Collections

' Define a custom section containing an individual
' element and a collection of elements.
Public Class UrlsSection
    Inherits ConfigurationSection

    <ConfigurationProperty("name", _
        DefaultValue:="MyFavorites", _
        IsRequired:=True, _
        IsKey:=False), _
        StringValidator( _
        InvalidCharacters:=" ~!@#$%^&*()[]{}/;'""|\", _
        MinLength:=1, MaxLength:=60)> _
        Public Property Name() As String

        Get
            Return CStr(Me("name"))
        End Get
        Set(ByVal value As String)
            Me("name") = value
        End Set
    End Property
    
    ' Declare an element (not in a collection) of the type
    ' UrlConfigElement. In the configuration
    ' file it corresponds to <simple .... />.
    <ConfigurationProperty("simple")> _
        Public ReadOnly Property Simple() _
        As UrlConfigElement

        Get
            Dim url As UrlConfigElement = _
                CType(Me("simple"),  _
                UrlConfigElement)
            Return url
        End Get
    End Property
    
    ' Declare a collection element represented 
    ' in the configuration file by the sub-section
    ' <urls> <add .../> </urls> 
    ' Note: the "IsDefaultCollection = false" 
    ' instructs the .NET Framework to build a nested 
    ' section like <urls> ...</urls>.
    <ConfigurationProperty("urls", _
        IsDefaultCollection:=False)> _
        Public ReadOnly Property Urls() _
        As UrlsCollection

        Get
            Dim urlsCollection _
                As UrlsCollection = _
                CType(Me("urls"), UrlsCollection)
            Return urlsCollection
        End Get
    End Property

    Protected Overrides Sub DeserializeSection( _
        ByVal reader As System.Xml.XmlReader)

        MyBase.DeserializeSection(reader)
        ' Enter your custom processing code here.
    End Sub

    Protected Overrides Function SerializeSection( _
        ByVal parentElement As ConfigurationElement, _
        ByVal name As String, _
        ByVal saveMode As ConfigurationSaveMode) As String

        Dim s As String = _
            MyBase.SerializeSection(parentElement, _
            name, saveMode)
        ' Enter your custom processing code here.
        Return s
    End Function 'SerializeSection
End Class

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

namespace Samples.AspNet
{
    public class UrlsCollection : ConfigurationElementCollection
    {
        public UrlsCollection()
        {
            // Add one url to the collection.  This is
            // not necessary; could leave the collection 
            // empty until items are added to it outside
            // the constructor.
            UrlConfigElement url = 
                (UrlConfigElement)CreateNewElement();
            Add(url);
        }

        public override 
            ConfigurationElementCollectionType CollectionType
        {
            get
            {
                return 

                    ConfigurationElementCollectionType.AddRemoveClearMap;
            }
        }

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

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

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

        public new string AddElementName
        {
            get
            { return base.AddElementName; }

            set
            { base.AddElementName = value; }
        }

        public new string ClearElementName
        {
            get
            { return base.ClearElementName; }

            set
            { base.ClearElementName = value; }
        }

        public new string RemoveElementName
        {
            get
            { return base.RemoveElementName; }
        }

        public new int Count
        {
            get { return base.Count; }
        }

        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);
            // Add custom code here.
        }

        protected override void 
            BaseAdd(ConfigurationElement element)
        {
            BaseAdd(element, false);
            // Add custom code here.
        }

        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();
            // Add custom code here.
        }
    }
}

Imports System.Configuration
Imports System.Collections

Public Class UrlsCollection
    Inherits ConfigurationElementCollection

    Public Sub New()
        ' Add one url to the collection.  This is
        ' not necessary; could leave the collection 
        ' empty until items are added to it outside
        ' the constructor.
        Dim url As UrlConfigElement = _
            CType(CreateNewElement(), UrlConfigElement)
        ' Add the element to the collection.
        Add(url)
    End Sub

    Public Overrides ReadOnly Property CollectionType() _
        As ConfigurationElementCollectionType

        Get
            Return ConfigurationElementCollectionType.AddRemoveClearMap
        End Get
    End Property

    Protected Overloads Overrides Function CreateNewElement() _
        As ConfigurationElement

        Return New UrlConfigElement()
    End Function 'CreateNewElement

    Protected Overloads Overrides Function CreateNewElement( _
        ByVal elementName As String) _
        As ConfigurationElement

        Return New UrlConfigElement(elementName)
    End Function 'CreateNewElement

    Protected Overrides Function GetElementKey( _
        ByVal element As ConfigurationElement) As [Object]

        Return CType(element, UrlConfigElement).Name
    End Function 'GetElementKey

    Public Shadows Property AddElementName() As String

        Get
            Return MyBase.AddElementName
        End Get

        Set(ByVal value As String)
            MyBase.AddElementName = value
        End Set
    End Property

    Public Shadows Property ClearElementName() As String
        Get
            Return MyBase.ClearElementName
        End Get

        Set(ByVal value As String)
            MyBase.ClearElementName = value
        End Set
    End Property

    Public Shadows ReadOnly Property RemoveElementName() As String
        Get
            Return MyBase.RemoveElementName
        End Get
    End Property

    Public Shadows ReadOnly Property Count() As Integer
        Get
            Return MyBase.Count
        End Get
    End Property

    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)
        ' Add custom code here.
    End Sub

    Protected Overrides Sub BaseAdd( _
    ByVal element As ConfigurationElement)
        BaseAdd(element, False)
        ' Add custom code here.
    End Sub

    Public Overloads Sub Remove( _
        ByVal url As UrlConfigElement)

        If BaseIndexOf(url) >= 0 Then
            BaseRemove(url.Name)
        End If
    End Sub

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

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

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

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

namespace Samples.AspNet
{
    public class UrlConfigElement : ConfigurationElement
    {
        // Constructor allowing name, url, and port to be specified.
        public UrlConfigElement(String newName,
            String newUrl, int newPort)
        {
            Name = newName;
            Url = newUrl;
            Port = newPort;
        }

        // Default constructor, will use default values as defined
        // below.
        public UrlConfigElement()
        {
        }

        // Constructor allowing name to be specified, will take the
        // default values for url and port.
        public UrlConfigElement(string elementName)
        {
            Name = elementName;
        }

        [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;
            }
        }

        protected override void DeserializeElement(
           System.Xml.XmlReader reader, 
            bool serializeCollectionKey)
        {
            base.DeserializeElement(reader, 
                serializeCollectionKey);
            // You can your custom processing code here.
        }

        protected override bool SerializeElement(
            System.Xml.XmlWriter writer, 
            bool serializeCollectionKey)
        {
            bool ret = base.SerializeElement(writer, 
                serializeCollectionKey);
            // You can enter your custom processing code here.
            return ret;
        }

        protected override bool IsModified()
        {
            bool ret = base.IsModified();
            // You can enter your custom processing code here.
            return ret;
        }
    }
}

Imports System.Configuration
Imports System.Collections

Public Class UrlConfigElement
    Inherits ConfigurationElement

    ' Constructor allowing name, url, and port to be specified.
    Public Sub New(ByVal newName As String, _
        ByVal newUrl As String, _
        ByVal newPort As Integer)

        Name = newName
        Url = newUrl
        Port = newPort

    End Sub

    ' Default constructor, will use default values as defined
    Public Sub New()

    End Sub


    ' Constructor allowing name to be specified, will take the
    ' default values for url and port.
    Public Sub New(ByVal elementName As String)
        Name = elementName

    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 Fix(Me("port"))
        End Get
        Set(ByVal value As Integer)
            Me("port") = value
        End Set
    End Property


    Protected Overrides Sub DeserializeElement(ByVal reader _
        As System.Xml.XmlReader, _
        ByVal serializeCollectionKey As Boolean)

        MyBase.DeserializeElement(reader, _
            serializeCollectionKey)
        ' Enter your custom processing code here.
    End Sub

    Protected Overrides Function SerializeElement(ByVal writer _
        As System.Xml.XmlWriter, _
        ByVal serializeCollectionKey As Boolean) As Boolean

        Dim ret As Boolean = _
            MyBase.SerializeElement(writer, serializeCollectionKey)
        ' Enter your custom processing code here.
        Return ret
    End Function 'SerializeElement

    Protected Overrides Function IsModified() As Boolean
        Dim ret As Boolean = MyBase.IsModified()
        ' Enter your custom processing code here.
        Return ret

    End Function 'IsModified
End Class

Remarks

The ConfigurationElement is an abstract class that is used to represent an XML element in a configuration file (such as Web.config). An element in a configuration file can contain zero, one, or more child elements.

Because the ConfigurationElement class is defined as abstract, you cannot create an instance of it. You can only derive classes from it. The .NET Framework includes classes that derive from the ConfigurationElement class in order to represent standard XML configuration elements, such as ConfigurationSection. You can also extend the ConfigurationElement class to access custom configuration elements and sections. The example included later in this topic shows how to access custom configuration elements and sections by using custom classes that derive from ConfigurationElement.

You can also extend the standard configuration types such as ConfigurationElement, ConfigurationElementCollection, ConfigurationProperty, and ConfigurationSection. For more information, see the documentation for those classes.

For more information about how to access information in configuration files, see the ConfigurationManager class and the WebConfigurationManager class.

Notes to Implementers

Every ConfigurationElement object creates an internal ConfigurationPropertyCollection collection of ConfigurationProperty objects that represents either the element attributes or a collection of child elements.

Non-customizable information and functionality is contained by an ElementInformation object provided by the ElementInformation property.

You can use either a programmatic or a declarative (attributed) coding model to create a custom configuration element:

• The programmatic model requires that for each element attribute, you create a property to get or set its value and add it to the internal property bag of the underlying ConfigurationElement base class. For an example of how to use this model, see the ConfigurationSection class.

• The simpler declarative model, also called the attributed model, allows you to define an element attribute by using a property and then decorate it with attributes. These attributes instruct the ASP.NET configuration system about the property types and their default values. With this information, obtained through reflection, the ASP.NET configuration system creates the element property objects for you and performs the required initialization. The example shown later in this topic shows how to use this model.

See also

• ConfigurationManager
• WebConfigurationManager
• ConfigurationSection
• ElementInformation
• ConfigurationElementCollection
• ConfigurationElementCollectionType
• ConfigurationProperty
• ConfigurationPropertyCollection