ConfigurationElement Class (System.Configuration)

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Microsoft Visual Studio 2008/.NET Framework 3.5

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.NET Framework Class Library

ConfigurationElement Class

Represents a configuration element within a configuration file.

Namespace: System.Configuration
Assembly: System.Configuration (in System.Configuration.dll)

Syntax

Visual Basic (Declaration)

Public MustInherit Class ConfigurationElement

Visual Basic (Usage)

Dim instance As ConfigurationElement

public abstract class ConfigurationElement

Visual C++

public ref class ConfigurationElement abstract

JScript

public abstract class ConfigurationElement

Remarks

The ConfigurationElement is an abstract class, so you cannot create an instance of it. It represents an XML element within a configuration file, such as the Web.config file.

Note:
An element within a configuration file refers to a basic XML element or a section. The basic element is a simple XML tag with related attributes, if any. In its simplest form, a section coincides with a basic element. Complex sections can contain one or more basic elements, a collection of elements, and other sections.

The ConfigurationElement is used as the base class for the classes representing XML configuration elements, such as ConfigurationSection.

You can extend the ConfigurationElement class to represent a configuration element within a ConfigurationSection section. You can also create a ConfigurationElementCollection collection of ConfigurationElement elements, as shown in the Example section.

Handling Configuration

To handle configuration information using the standard types, use one of the following approaches:

Accessing a section. To access configuration information for your application you must use one of the GetSection methods provided by ConfigurationManager and WebConfigurationManager. For special sections such as appSettings and connectionStrings, you use the AppSettings property of the ConfigurationManager class or the AppSettings property of the WebConfigurationManager class, and the ConnectionStrings property of the ConfigurationManager class or the ConnectionStrings property of the WebConfigurationManager class. These methods perform read-only operations, use a single cached instance of the configuration, and are multithread aware.
Accessing configuration files. Your application can read and write configuration settings at any level, for itself or for other applications or computers as a whole, locally or remotely. You use one of the open methods provided by the ConfigurationManager class and the WebConfigurationManager class. These methods will return a Configuration object, which in turn provides the required methods and properties to handle the underlying configuration files. These methods perform read or write operations and recreate the configuration data every time a file is opened.
Advanced configuration. More advanced configuration handling is provided by the types SectionInformation, PropertyInformation, PropertyInformationCollection, ElementInformation, ContextInformation, ConfigurationSectionGroup, and ConfigurationSectionGroupCollection.

Extending Configuration Standard Types

You can also extend the standard configuration types such as ConfigurationElement, ConfigurationElementCollection, ConfigurationProperty, and ConfigurationSection, using either a programmatic or a declarative (attributed) model. For an example of how to extend a standard configuration type programmatically, see to the ConfigurationSection class. For an example of how to extend a standard configuration type using the attributed mode, see the ConfigurationElement class.

Notes to Implementers:

Configuration is the class that allows programmatic access for editing configuration files. You use one of the open methods provided by WebConfigurationManager for Web applications or by ConfigurationManager for client applications. These methods will return a Configuration object, which in turn provides the required methods and properties to handle the underlying configuration files. You can access these files for reading or writing as explained in the following sections:

Reading. You use GetSection or GetSectionGroup to read configuration information. Note that the user or process that reads must have the following permissions:

Read permission on the configuration file at the current configuration hierarchy level.
Read permissions on all the parent configuration files.

If your application needs read-only access to its own configuration, it is recommended that you use one of the GetSection overloaded methods in the case of Web applications. Or the GetSection method in the case of client applications.

These methods provide access to the cached configuration values for the current application, which has better performance than the Configuration class.

Note:
If you use a static GetSection method that takes a path parameter, the path parameter must refer to the application in which the code is running; otherwise, the parameter is ignored and configuration information for the currently-running application is returned.

Writing. You use one of the Save methods to write configuration information. Note that the user or process that writes must have the following permissions:
- Write permission on the configuration file and directory at the current configuration hierarchy level.
- Read permissions on all the configuration files.

Notes to Inheritors:

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.
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.

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 five files: the custom ConfigurationElement class, the custom ConfigurationElementCollection class, the custom ConfigurationSection class, a Main method for running the example as a console application, and an app.config file

Visual Basic

Imports System
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 'New

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

    End Sub 'New


    ' 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 'New


    <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 'DeserializeElement

    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 'UrlConfigElement

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;
        }
    }
}

Visual Basic

Imports System
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 'New

    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.AddElementName = 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 'Add

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

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.AddElementName = 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.
        }
    }
}

Visual Basic

Imports System
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 'DeserializeSection

    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 'UrlsSection

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;
        }

    }
}

Visual Basic

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

// 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();
        }
    }
}

<configuration>
    <configSections>
        <section name="MyUrls" type="Samples.AspNet.UrlsSection, ConfigurationElement, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" allowDefinition="Everywhere" allowExeDefinition="MachineToApplication" restartOnExternalChanges="true" />
    </configSections>
    <MyUrls name="MyFavorites">
    <simple name="Microsoft1" url="http://www.microsoft1.com" port="1" />
    <urls>
      <clear />
      <add name="Microsoft2" url="http://www.microsoft2.com" port="2" />
      <add name="Contoso" url="http://www.contoso.com" port="8080" />
    </urls>
    </MyUrls>
</configuration>

Inheritance Hierarchy

Thread Safety

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Platforms

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

Version Information

.NET Framework

Supported in: 3.5, 3.0, 2.0

Reference

ConfigurationElement Members

System.Configuration Namespace

ElementInformation

ConfigurationElementCollection

ConfigurationElementCollectionType

ConfigurationProperty

ConfigurationPropertyCollection

ConfigurationSection