Interop type cannot be embedded

Question

I am creating a web application on the .NET 4.0 framework (beta2) in C#.

When I try to use a assembly called "ActiveHomeScriptLib", I get the following error:

Interop type 'ActiveHomeScriptLib.ActiveHomeClass' cannot be embedded. Use the applicable interface instead.

When I change the framework to version 3.5, I don't have any errors.

What is an Interop Type and why does this only occur when I use the 4.0 framework?

Answer 1

http://digital.ni.com/public.nsf/allkb/4EA929B78B5718238625789D0071F307

This error occurs because the default value is true for the Embed Interop Types property of the TestStand API Interop assembly referenced in the new project. To resolve this error, change the value of the Embed Interop Types property to False by following these steps: Select the TestStand Interop Assembly reference in the references section of your project in the Solution Explorer. Find the Embed Interop Types property in the Property Browser, and change the value to False

Answer 2

.NET 4.0 allows primary interop assemblies (or rather, the bits of it that you need) to be embedded into your assembly so that you don't need to deploy them alongside your application.

For whatever reason, this assembly can't be embedded - but it sounds like that's not a problem for you. Just open the Properties tab for the assembly in Visual Studio 2010 and set "Embed Interop Types" to "False".

EDIT: See also Michael Gustus's answer, removing the Class suffix from the types you're using.

Answer 3

Expanding on Jon's correct answer.

The problem here is that your are combining the new "Embed Interop Types" (or NoPIA) feature with use of a class type. The "Embed Interop Types" feature works by essentially statically linking in all of the types from a PIA (Primary Interop Assembly) into the referencing assembly removing the overhead of deploying it.

This feature works great for most types in a PIA but it does have restrictions. One of them is that you cannot embed classes (it's a servicing issue). Misha has a detailed blog article on why this is not allowed

• http://blogs.msdn.com/mshneer/archive/2009/12/07/interop-type-xxx-cannot-be-embedded-use-the-applicable-interface-instead.aspx

Answer 4

I ran into this issue when pulling down a TFS project to my local machine. Allegedly, it was working fine on the guy's machine who wrote it. I simply changed this...

WshShellClass shellClass = new WshShellClass();

To this...

WshShell shellClass = new WshShell();

Now, it is working like a champ!

Answer 5

I had same problem in VB.NET 2013 with Office 2007, and this solved it:

VS 2013 VB.NET Project > Props > Refs > Microsoft Word 12.0 Object Lib > Embed Interop Types: change True to False

Answer 6

In most cases, this error is the result of code which tries to instantiate a COM object. For example, here is a piece of code starting up Excel:

Excel.ApplicationClass xlapp = new Excel.ApplicationClass();

Typically, in .NET 4 you just need to remove the 'Class' suffix and compile the code:

Excel.Application xlapp = new Excel.Application();

An MSDN explanation is here.