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ImportedFromTypeLibAttribute Class

Indicates that the types defined within an assembly were originally defined in a type library.

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

[AttributeUsageAttribute(AttributeTargets.Assembly, Inherited = false)]
public sealed class ImportedFromTypeLibAttribute : Attribute

You can apply this attribute to assemblies, although the Type Library Importer (Tlbimp.exe) typically applies it for you when it a type library.

The primary use of the attribute is to capture the original source of the type information. For example, you can import A.tlb as an interop assembly called A.dll and have assembly B.dll reference A.dll. When you export B.dll to B.tlb, this attribute causes the references in B.tlb that point to A.dll to point instead to A.tlb. This should not be confused with the ComImportAttribute, which specifies that an individual type is implemented in COM.

using System;
using System.Reflection;
using System.Runtime.InteropServices;

namespace A
	class ClassA
		public static bool IsCOMAssembly( Assembly a )
			object[] AsmAttributes = a.GetCustomAttributes( typeof( ImportedFromTypeLibAttribute ), true );
			if( AsmAttributes.Length > 0 )
				ImportedFromTypeLibAttribute imptlb = ( ImportedFromTypeLibAttribute )AsmAttributes[0];
				string strImportedFrom  = imptlb.Value;
				// Print out the the name of the DLL from which the assembly is imported.
				Console.WriteLine( "Assembly " + a.FullName + " is imported from " + strImportedFrom );
				return true;
			// This is not a COM assembly.
			Console.WriteLine( "Assembly " + a.FullName + " is not imported from COM" );
			return false;


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, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC

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