Skip to main content

VS 2010: Interop type cannot be embedded. Use the applicable interface instead.

For a recent project we had to use the Excel Interop Assembly. But after referencing the Interop Assembly in Visual Studio 2010, we get an error when we try to compile.  Setting the "Embed Interop Types" to FALSE  solves the problem but of course than we loose a nice new feature in Visual Studio 2010.

So where does this error comes from? One of the limitations for 'Embed Interop Types' feature has been that classes cannot be used when embedding an assembly. This limitation has to do with servicing - it is safe to embed metadata but not anything that can potentially contain executable code (class types contain metadata AND code while interfaces only contain metadata). When you try to references a class type from an Interop Assembly for which the "Embed Interop Types" is set to TRUE compiler do issue a warning.

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

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


Here it is enough to say that Excel.ApplicationClass derives from Excel.Application interface and one can even instantiate Excel using Excel.Application interface. Rewriting this code as below produces exact same results:

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

Typically, to change your code to use an interface type instead of a class type you just need to remove the 'Class' suffix and compile the code! Another way to find what the applicable interface is - look at the definition of the class type. The class usually derives from one or more interfaces. Look at the definition of each interface - one of them will have CoClass attribute and this is the interface that you are looking for.

Labels:

Popular posts from this blog

Podman– Command execution failed with exit code 125

After updating WSL on one of the developer machines, Podman failed to work. When we took a look through Podman Desktop, we noticed that Podman had stopped running and returned the following error message: Error: Command execution failed with exit code 125 Here are the steps we tried to fix the issue: We started by running podman info to get some extra details on what could be wrong: >podman info OS: windows/amd64 provider: wsl version: 5.3.1 Cannot connect to Podman. Please verify your connection to the Linux system using `podman system connection list`, or try `podman machine init` and `podman machine start` to manage a new Linux VM Error: unable to connect to Podman socket: failed to connect: dial tcp 127.0.0.1:2655: connectex: No connection could be made because the target machine actively refused it. That makes sense as the podman VM was not running. Let’s check the VM: >podman machine list NAME         ...
Read more

Cache stampede: when our cache turned against us

While investigating some performance issues, we ran into an ASP.NET Core API that cached a fairly expensive aggregation query for 60 seconds. Under normal load, that was fine: one request rebuilds the cache, everyone else reads from it. Under peak load, dozens of requests would arrive in that same expiry window, all see a cache miss, and all fire the same expensive query in parallel. The database didn't like that. That was the moment when our caching layer stopped helping and started hurting. A burst of requests comes in at the same time, all miss the cache, and all go hammer the database or the downstream API at once. That's a cache stampede . The cache was supposed to protect our backend, and for a few hundred milliseconds it did the opposite. Why this happens IMemoryCache.GetOrCreate (and its async sibling) looks like it protects you, but it doesn't add any locking on its own. Look at the naive version: public async Task<Report> GetReportAsync(string key) ...
Read more

A complex system designed from scratch never works

A few years ago, I worked as an architect on a big mainframe rewrite. I still count it as one of my failures. Not because the technology was wrong, but because I couldn't convince the management team to simplify the approach. Years later, the organization is still struggling to get the new system up and running. I left the project at the time, because I couldn't put my name behind an approach that would take very long and cost a lot of money without a working system to show for it along the way. Gall’s Law That memory keeps coming back to me, because it's a textbook case of Gall's Law playing out in real life. Gall's Law , from John Gall's Systemantics , states it plainly: A complex system that works is invariably found to have evolved from a simple system that worked. A complex system designed from scratch never works, and it cannot be patched to make it work. You have to start over with a simple system that works. What does that mean in practice,...
Read more