com-interop

Apparently, managed handlers for events, sourced from an unmanaged out-of-process COM server, are called back on a random pool thread, rather than on the main STA thread (as I'd expect). I've discovered this while answering a question on Internet Explorer automation . In the code below, DocumentComplete is fired on a non-UI thread (so "Event thread" is not the same as "Main thread" in the debug output). Thus, I have to use this.Invoke to show a message box. To the best of my knowledge, this behavior is different from unmanaged COM clients, where events subscribed to from an STA thread are

.NET objects are free-threaded by default. If marshaled to another thread via COM, they always get marshaled to themselves, regardless of whether the creator thread was STA or not, and regardless of their ThreadingModel registry value. I suspect, they aggregate the Free Threaded Marshaler (more details about COM threading could be found here ). I want to make my .NET COM object use the standard COM marshaller proxy when marshaled to another thread. The problem: using System; using System.Runtime.InteropServices; using System.Threading; using System.Threading.Tasks; using System.Windows

I am creating a wrapper class in .NET (VB.NET as it happens but is equally related to C#) that is exposed to COM and one of the properties I am trying to wrap is a Variant. I thought I would just be able to use an Object, but I get an error: Public Property FieldValue([vFieldID As Object = -1]) As Object cannot be exposed to COM as a property 'Let'. You will not be able to assign non-object values (such as numbers or strings) to this property from Visual Basic 6.0 using a 'Let' statement.* My property declaration looks like this: Public Property FieldValue(Optional ByVal vFieldID As Object =

I am attempting to return a collection of departments from a .NET assembly to be consumed by ASP via COM Interop. Using .NET I would just return a generic collection, e.g. List<Department> , but it seems that generics don't work well with COM Interop. So, what are my options? I would like to both iterate over the list and be able to access an item by index. Should I inherit from List<Department> , implement an IList , IList<Department> or another interface, or is there a better way? Ideally I would prefer not to have to implement a custom collection for every type of list I need. Also, will

Consider the following C# code using a COM object. MyComObject o = new MyComObject; try { var baz = o.Foo.Bar.Baz; try { // do something with baz } finally { Marshal.ReleaseComObject(baz); } } finally { Marshal.ReleaseComObject(o); } This will release the COM objects o and baz , but not the temporary objects returnd by o.Foo and o.Foo.Bar . This can cause problems, when those objects hold a large amount of unmanaged memory or other resources. An obvious but ugly solution would be, to clutter the code even more with try-finally and Marshal.ReleaseComObject . See C# + COM Interop, deterministic

What exactly does the VS project option "Register for COM interop" actually do? Because when I build my library with this option enabled I can call CreateObject on my library from VBScript. But if I build without this and then run regasm manually CreateObject fails. So I'm wondering -- what does VS2010 do that I'm not doing? It does the same thing as running Regasm.exe with the /tlb and /codebase options. The /codebase option is probably the one you forgot. Regasm likes assuming you put the DLL in the GAC and generates a warning when you don't. The GAC is indeed a very good way to avoid DLL