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Assembly.IsDefined Method

Indicates whether or not a specified attribute has been applied to the assembly.

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

public virtual bool IsDefined(
	Type attributeType,
	bool inherit


Type: System.Type

The Type of the attribute to be checked for this assembly.

Type: System.Boolean

This argument is ignored for objects of this type.

Return Value

Type: System.Boolean
true if the attribute has been applied to the assembly; otherwise, false.


_Assembly.IsDefined(Type, Boolean)
ICustomAttributeProvider.IsDefined(Type, Boolean)


attributeType is null.


attributeType uses an invalid type.


In the .NET Framework version 2.0, this method returns true if the assembly has security attributes stored in the new metadata format. Assemblies compiled with version 2.0 use this format. Dynamic assemblies and assemblies compiled with earlier versions of the .NET Framework use the old XML format. See Emitting Declarative Security Attributes.

The following code example applies the AssemblyTitleAttribute attribute to an assembly and then uses IsDefined to indicate whether it was applied. It also tests an attribute that was not applied.

using System;
using System.Reflection;

// Set an assembly attribute.
[assembly:AssemblyTitleAttribute("A title example")]

// Note that the suffix "Attribute" can be omitted:
// [assembly:AssemblyTitle("A title example")]

public class Test {

    public static void Main() {

        // Get the assembly that is executing this method.
        Assembly asm = Assembly.GetCallingAssembly();

        // Get the attribute type just defined.
        Type aType = typeof(AssemblyTitleAttribute);
        Console.WriteLine(asm.IsDefined(aType, false));

        // Try an attribute not defined.
        aType = typeof(AssemblyVersionAttribute);
        Console.WriteLine(asm.IsDefined(aType, false));
//  This code example produces the following output: 
//  True 
//  False 

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, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

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, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5, 2.0

XNA Framework

Supported in: 3.0, 2.0, 1.0