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Attribute.TypeId Property

When implemented in a derived class, gets a unique identifier for this Attribute.

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

public virtual Object TypeId { get; }

Property Value

Type: System.Object
An Object that is a unique identifier for the attribute.

As implemented, this identifier is merely the Type of the attribute. However, it is intended that the unique identifier be used to identify two attributes of the same type.

The following code example implements the TypeId property in a custom parameter Attribute class and shows its use.

// Example for the Attribute.TypeId property. 
using System;
using System.Reflection;

namespace NDP_UE_CS 
{
    // Define a custom parameter attribute that takes a single message argument.
    [AttributeUsage( AttributeTargets.Parameter )]
    public class ArgumentUsageAttribute : Attribute
    {
        // The constructor saves the message and creates a unique identifier. 
        public ArgumentUsageAttribute( string UsageMsg )
        {
            this.usageMsg = UsageMsg;
            this.instanceGUID = Guid.NewGuid( );
        }

        // This is storage for the attribute message and unique ID. 
        protected string usageMsg;
        protected Guid instanceGUID;

        // This is the Message property for the attribute. 
        public string Message
        {
            get { return usageMsg; }
            set { usageMsg = value; }
        }

        // Override TypeId to provide a unique identifier for the instance. 
        public override object TypeId
        {
            get { return (object)instanceGUID; }
        }

        // Override ToString() to append the message to what the base generates. 
        public override string ToString( )
        {
            return base.ToString( ) + ":" + usageMsg;
        }
    }

    public class TestClass 
    {
        // Assign an ArgumentUsage attribute to each parameter. 
        // Assign a ParamArray attribute to strList using the params keyword. 
        public void TestMethod(
            [ArgumentUsage("Must pass an array here.")]
            String[] strArray,
            [ArgumentUsage("Can pass a param list or array here.")]
            params String[] strList)
        { }
    }

    class AttributeTypeIdDemo 
    {
        static void ShowAttributeTypeIds( ) 
        {
            // Get the class type, and then get the MethodInfo object  
            // for TestMethod to access its metadata.
            Type clsType = typeof( TestClass );
            MethodInfo mInfo = clsType.GetMethod("TestMethod");

            // There will be two elements in pInfoArray, one for each parameter.
            ParameterInfo[] pInfoArray = mInfo.GetParameters();
            if (pInfoArray != null) 
            {
                // Create an instance of the param array attribute on strList.
                ParamArrayAttribute listArrayAttr = (ParamArrayAttribute)
                    Attribute.GetCustomAttribute( pInfoArray[1], 
                        typeof(ParamArrayAttribute) );

                // Create an instance of the argument usage attribute on strArray.
                ArgumentUsageAttribute arrayUsageAttr1 = (ArgumentUsageAttribute)
                    Attribute.GetCustomAttribute( pInfoArray[0], 
                        typeof(ArgumentUsageAttribute) );

                // Create another instance of the argument usage attribute  
                // on strArray.
                ArgumentUsageAttribute arrayUsageAttr2 = (ArgumentUsageAttribute)
                    Attribute.GetCustomAttribute( pInfoArray[0], 
                        typeof(ArgumentUsageAttribute) );

                // Create an instance of the argument usage attribute on strList.
                ArgumentUsageAttribute listUsageAttr = (ArgumentUsageAttribute)
                    Attribute.GetCustomAttribute( pInfoArray[1], 
                        typeof(ArgumentUsageAttribute) );

                // Display the attributes and corresponding TypeId values.
                Console.WriteLine( "\n\"{0}\" \nTypeId: {1}",
                    listArrayAttr.ToString(), listArrayAttr.TypeId );
                Console.WriteLine( "\n\"{0}\" \nTypeId: {1}",
                    arrayUsageAttr1.ToString(), arrayUsageAttr1.TypeId );
                Console.WriteLine( "\n\"{0}\" \nTypeId: {1}",
                    arrayUsageAttr2.ToString(), arrayUsageAttr2.TypeId );
                Console.WriteLine( "\n\"{0}\" \nTypeId: {1}",
                    listUsageAttr.ToString(), listUsageAttr.TypeId );
            }
            else
                Console.WriteLine( "The parameters information could " +
                    "not be retrieved for method {0}.", mInfo.Name );
        }

        static void Main( ) 
        {
            Console.WriteLine( 
                "This example of the Attribute.TypeId property\n" +
                "generates the following output." );
            Console.WriteLine( 
                "\nCreate instances from a derived Attribute " +
                "class that implements TypeId, \nand then " +
                "display the attributes and corresponding TypeId values:" );

            ShowAttributeTypeIds( );
        }
    }
}

/*
This example of the Attribute.TypeId property
generates the following output.

Create instances from a derived Attribute class that implements TypeId,
and then display the attributes and corresponding TypeId values:

"System.ParamArrayAttribute"
TypeId: System.ParamArrayAttribute

"NDP_UE_CS.ArgumentUsageAttribute:Must pass an array here."
TypeId: d03a23f4-2536-4478-920f-8b0426dec7f1

"NDP_UE_CS.ArgumentUsageAttribute:Must pass an array here."
TypeId: a1b412e8-3047-49fa-8d03-7660d37ef718

"NDP_UE_CS.ArgumentUsageAttribute:Can pass a param list or array here."
TypeId: 7ac2bf61-0327-48d6-a07e-eb9aaf3dd45e
*/

.NET Framework

Supported in: 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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

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