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MS-Windows Troubleshooting


error CS1752: Interop type 'Some.Type' cannot be embedded


Symptom:

When compiling the following error is generated:

error CS1752: Interop type 'Some.Type' cannot be embedded. Use the applicable interface instead.

where Some.Type[] is the COM type you are trying to use.

This may also be accompanied with the error:

error CS0143: The type 'Some.Type' has no constructors defined

Annoyingly in the Visual Studio "Error List" only the second of these errors ("The type ... has no constructors defined.") may be shown, and to see the real errors you will need to view the "Output".

Cause:

One of the enhancements introduced with .NET 4 is that the common language runtime now supports embedding of type information for COM types directly into managed assemblies, instead of requiring the assembly to obtain type information from the interop assemblies.

If you want to read more about this then see the Microsoft msdn article "Type Equivalence and Embedded Interop Types"

This is why the error goes away if compiling for a .NET framework prior to .NET 4 - because the default behaviour has changed with .NET 4.

In the case of this error, the interop type information cannot be embedded. Hence the error. (I assume this is function of the COM assembly, but that is only a guess on my part.)

Possible Remedies:

  • Change the .NET framework to a framework prior to .NET 4.

    This probably is not an ideal solution.

  • Tell Visual Studio not to embed the interop types for that assembly.

    To do this in Visual Studio 2010:

    1. Identify the namespace: In the code where you have the error, right click on the type and select "Go To Definition". From this you should be able to identify the name of the namespace which contains the type - this is the name of the reference you will use below.
    2. In the Solution Explorer, expand the list of References for the project.

      If you are using VB rather than C# then you will need to look in the project settings for the list of references.

    3. Right click the the reference that you identified above in step 1, and select "Properties".
    4. In the reference's properties change the property "Embed Interop Types" from "True" to "False".

    The error should then disappear.


These notes have been tested within Microsoft Visual Studio .NET 2010 (.NET 4), and may apply to other versions as well.



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