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ConfigurationProperty Class

This API supports the .NET Framework infrastructure and is not intended to be used directly from your code.

Represents an attribute or a child of a configuration element. This class cannot be inherited.

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

public sealed class ConfigurationProperty

In the case of a simple ConfigurationElement, such as the CustomSection shown in the next example, the ConfigurationProperty objects represent attributes such as fileName.

In the case of more complex configuration elements such as a section containing subsections, for instance authentication, the ConfigurationProperty objects can represent ConfigurationElement objects as well as attributes.

The ConfigurationPropertyCollection class represents the collection of the ConfigurationProperty objects that can be either attributes or ConfigurationElement objects of a configuration element.

The ConfigurationProperty class represents an individual configuration setting. This class allows you to get or set the name, type, and default value for a particular configuration entity (attribute or element) and specify whether the attribute is required, is an element key, or represents a default element collection.

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 a programmatic or a declarative (attributed) coding model to create a custom configuration element.

  • Programmatic Model. This model requires that you create a property for each element attribute to get and/or set its value and add it to the internal property bag of the underlying ConfigurationElement base class.

  • Declarative Model. This simpler model, also called attributed model, allows you to define an element attribute by using a property and 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.

  1. The following code example shows how to use the ConfigurationProperty when you create a custom section.

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

namespace ConfigurationPropertyExample
    // Define a custom section. 
    // Shows how to use the ConfigurationProperty 
    // class when defining a custom section. 
    public sealed class CustomSection : ConfigurationSection
        // The collection (property bag) that contains  
        // the section properties. 
        private static ConfigurationPropertyCollection _Properties;

        // The FileName property. 
        private static ConfigurationProperty _FileName;

        // The Alias property. 
        private static ConfigurationProperty _Alias;

        // The MaxUsers property. 
        private static ConfigurationProperty _MaxUsers;

        // The MaxIdleTime property. 
        private static ConfigurationProperty _MaxIdleTime;

        // CustomSection constructor. 
        static CustomSection()
            // Initialize the _FileName property
            _FileName =
                new ConfigurationProperty("fileName",
                typeof(string), "default.txt");

            // Initialize the _MaxUsers property
            _MaxUsers =
                new ConfigurationProperty("maxUsers",
                typeof(long), (long)1000,

            // Initialize the _MaxIdleTime property
            TimeSpan minTime = TimeSpan.FromSeconds(30);
            TimeSpan maxTime = TimeSpan.FromMinutes(5);

            ConfigurationValidatorBase _TimeSpanValidator =
                new TimeSpanValidator(minTime, maxTime, false);

            _MaxIdleTime =
                new ConfigurationProperty("maxIdleTime",
                typeof(TimeSpan), TimeSpan.FromMinutes(5),
                "[Description:This is the max idle time.]");

            // Initialize the _Alias property
            _Alias =
                new ConfigurationProperty("alias",
                typeof(string), "alias.txt");

            // Initialize the Property collection.
            _Properties = new ConfigurationPropertyCollection();

        // Return the initialized property bag 
        // for the configuration element. 
        protected override ConfigurationPropertyCollection Properties
                return _Properties;

        // Clear the property. 
        public void ClearCollection()

        // Remove an element from the property collection. 
        public void RemoveCollectionElement(string elName)

        // Get the property collection enumerator. 
        public IEnumerator GetCollectionEnumerator()
            return (Properties.GetEnumerator());

        [StringValidator(InvalidCharacters = " ~!@#$%^&*()[]{}/;'\"|\\",
            MinLength = 1, MaxLength = 60)]
        public string FileName
                return (string)this["fileName"];
                this["fileName"] = value;

        [StringValidator(InvalidCharacters = " ~!@#$%^&*()[]{}/;'\"|\\",
            MinLength = 1, MaxLength = 60)]
        public string Alias
                return (string)this["alias"];
                this["alias"] = value;

        [LongValidator(MinValue = 1, MaxValue = 1000000,
            ExcludeRange = false)]
        public long MaxUsers
                return (long)this["maxUsers"];
                this["maxUsers"] = value;

        public TimeSpan MaxIdleTime
                return (TimeSpan)this["maxIdleTime"];
                this["maxIdleTime"] = value;

The following is an excerpt of the configuration file used by the code in the previous example.

    <section name="CustomSection" type="ConfigurationPropertyExample.CustomSection, ConfigurationPropertyExample" 
      allowDefinition="Everywhere" allowExeDefinition="MachineToApplication" 
      restartOnExternalChanges="true" />
  <CustomSection fileName="override.txt" alias="alias.txt" 
    maxUsers="1000" maxIdleTime="00:05:00" />

The following example shows how to create the previous section in code.

// Define a custom section programmatically. 
static void CreateSection()
        CustomSection customSection;

        // Get the current configuration file.
        System.Configuration.Configuration config =

        // Create the section entry   
        // in the <configSections> and the  
        // related target section in <configuration>. 
        // Call it "CustomSection2" since the file in this  
        // example already has "CustomSection".
        if (config.Sections["CustomSection"] == null)
            customSection = new CustomSection();
            config.Sections.Add("CustomSection2", customSection);
            customSection.SectionInformation.ForceSave = true;
    catch (ConfigurationErrorsException err)


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

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.

.NET Framework

Supported in: 3.5, 3.0, 2.0

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