Hi,

We have a COM library with a .NET extensibility model which is achieved
using managed C++ (2.0) to aggregate managed classes. All is fine unless a
managed class exposes a custom managed interface in which case casting to the
interface from fails. The problem is solved by adding the ComVisible(true)
attribute. The doc says however that true is the default. Is using
aggregation a special case where this attribute must be explicity set or am i
mistaken on it's use.

From the doc:

The default is true, which indicates that the managed type is visible to
COM. This attribute is not needed to make public managed assemblies and types
visible; they are visible to COM by default.

Thanks,
Steve

Steve,

There was an argument (discussion) about this a few weeks back. I
thought I'd try a little test and this is what I've found.

C#.NET 2003
- Create a new Class Library
- Set the "Register for COM Interop
- Build --> Sucess

C#.NET 2005 Express
- Create a new Class Library
- Set the "Register for COM Interop
- Build --> Fail (.dll does not contain any types that can be registered
for COM Interop)
- Decorate your class with [ComVisible(true)]
- Build --> Success

It would appear to me that in 2.0, it is not the default.

Jason Newell


Steve wrote:

Don't know about Express, but it's definitely not the case with VS Team
System.
But lets forget about VS versions and just try to build and register a class
from the command line (using Regasm.exe), you'll see that it works (it works
for me, and it should or it's a breaking issue). Can you try to register the
class that failed using regasm?

Willy.


"Jason Newell" <nospam (AT) nospam (DOT) com> wrote

Willy,

Here are the results.

- Created a new C# 2005 Express Class Library Project.
- Register for COM Interop will be left off.

using System;

namespace COMTest
{
public class Class1
{
}
}

- Execute Build
- Execute regasm
--------------------------------------------------------------------------
C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727>rega sm
C:\Test\COMTest\COMTest\bin\Release\COMTest.dll
Microsoft (R) .NET Framework Assembly Registration Utility 2.0.50727.42
Copyright (C) Microsoft Corporation 1998-2004. All rights reserved.

RegAsm : warning RA0000 : No types were registered
--------------------------------------------------------------------------

- Change code like below.

using System;
using System.Runtime.InteropServices;

namespace COMTest
{
[ComVisible(true)]
public class Class1
{
}
}

- Execute Build
- Execute regasm
--------------------------------------------------------------------------
C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727>rega sm
C:\Test\COMTest\COMTest\bin\Release\COMTest.dll
Microsoft (R) .NET Framework Assembly Registration Utility 2.0.50727.42
Copyright (C) Microsoft Corporation 1998-2004. All rights reserved.

Types registered successfully
--------------------------------------------------------------------------

So Willy, am I doing something wrong here? I have 2 years experience
with COM Interop so I'm very familiar with how it works, in 1.1 anyway.
I'm just now starting to look at 2.0 hence my curiosity. Thanks.

Jason Newell


Willy Denoyette [MVP] wrote:

OK, I've figured out what's going on.

Assemblyinfo.cs has the following line by default from the template.

// Setting ComVisible to false makes the types in this assembly not visible
// to COM components. If you need to access a type in this assembly from
// COM, set the ComVisible attribute to true on that type.
[assembly: ComVisible(false)]


Jason Newell



Jason Newell wrote:

That explains it all, I didn't pay attention to the assemblyinfo.cs as I'm
using my own assemblyinfo.cs template file in my projects.
The VS team decided to overrule the default at the assembly level, so now
you have to apply the attribute to each individual class your want to make
visible.


Willy.



"Jason Newell" <nospam (AT) nospam (DOT) com> wrote

Thanks for find this guys. That does explain it all.

Steve

"Willy Denoyette [MVP]" wrote: