C# – C++ calling C# COM interop error: HRESULT 0x80131509

ccominterop

I create a C# COM interop for c++ to invoke.
I have registered the dll and tlb file by regasm.
everything goes well till one day i changed code of C# part (i didn't change the definition of interface, just implementation changed). one interface in COM returns an error 0x80131509. the strange thing is, it is only happened in some computers (my develop PC is works well so i can't debug this problem).
I'm not really clear on how the C# COM worked with C++, after i registered them, i just know they create key value in window registry.(like what regasm /regfile generated). how c++ knows where the COM dll is(search path environment variables)? and what the use of tlb file in run time?

any suggestion?

Best Answer

I got the same error as soon as I introduced a simple inheritance hierarchy to my COM library. A quick resolution was to set the ComVisible attribute to true on the base class. This fixed my problem immediately.

It does make a lot of sense when you think about it - the compiler doesn't allow you to build a hierarchy where the base class is less visible than the inheriting class. So it being the same for COM should come as no surprise - the only difference being, that it is failing at run-time instead of compile-time.

I would venture that the true reason for the error is a broken constructor chain, but I put no further research into it.

Related Solutions

C# – Calling the base constructor in C#

Modify your constructor to the following so that it calls the base class constructor properly:

public class MyExceptionClass : Exception
{
    public MyExceptionClass(string message, string extrainfo) : base(message)
    {
        //other stuff here
    }
}

Note that a constructor is not something that you can call anytime within a method. That's the reason you're getting errors in your call in the constructor body.

C# – How to properly clean up Excel interop objects

Excel does not quit because your application is still holding references to COM objects.

I guess you're invoking at least one member of a COM object without assigning it to a variable.

For me it was the excelApp.Worksheets object which I directly used without assigning it to a variable:

Worksheet sheet = excelApp.Worksheets.Open(...);
...
Marshal.ReleaseComObject(sheet);

I didn't know that internally C# created a wrapper for the Worksheets COM object which didn't get released by my code (because I wasn't aware of it) and was the cause why Excel was not unloaded.

I found the solution to my problem on this page, which also has a nice rule for the usage of COM objects in C#:

Never use two dots with COM objects.

So with this knowledge the right way of doing the above is:

Worksheets sheets = excelApp.Worksheets; // <-- The important part
Worksheet sheet = sheets.Open(...);
...
Marshal.ReleaseComObject(sheets);
Marshal.ReleaseComObject(sheet);

POST MORTEM UPDATE:

I want every reader to read this answer by Hans Passant very carefully as it explains the trap I and lots of other developers stumbled into. When I wrote this answer years ago I didn't know about the effect the debugger has to the garbage collector and drew the wrong conclusions. I keep my answer unaltered for the sake of history but please read this link and don't go the way of "the two dots": Understanding garbage collection in .NET and Clean up Excel Interop Objects with IDisposable

Best Answer

Related Solutions

C# – Calling the base constructor in C#

C# – How to properly clean up Excel interop objects

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