Using a C# EXE to interact with AutoCAD

I'm updating this because I've found out that the method explained below has problems, and that you'd do better making a C# DLL to run inside AutoCAD, or use C# with ObjectDBX to run as an EXE which talks to AutoCAD.

The problem is that Microsoft changed the way .NET works, details here, which means that Documents.Open  can sometimes fail. The error code is HRESULT: 0x80010001 (RPC_E_CALL_REJECTED). It is to do with the fact that AutoCAD is still initializing when the call is made, so you need to add some sort of delay, or catch an exception, or maybe wait till it is visible. This is my solution, though I don't like having to do this:

            AcadDocument AcadDoc = null;

            int iNumTries = 0;
            const int ikMaxTries = 400;
            while (iNumTries < ikMaxTries)
            {
                bool bError = false ;
                try
                {
                    AcadDoc = AcadApp.Documents.Open(@"C:\DisegniSviluppati\04.DWG");
                    AcadDoc.Activate();
                }

                catch (Exception e1)
                {
                    Debug.WriteLine("Catch on try " + iNumTries.ToString() + ", exception: " + e1.Message + "\n");
                    bError = true;
                }

                if (!bError)
                {
                    break;
                }

                if (iNumTries == ikMaxTries)
                {
                    break;
                }

                iNumTries++;
            }

            if (iNumTries == ikMaxTries)
            {
                // Failure
                return;
            }

            // Now we will loop over all the entities in the drawing we have just saved and re-opened...
            var ModelSpace = AcadDoc.ModelSpace;
            int iNumEntities = ModelSpace.Count;

Essentially I stay in a loop trying to open the drawing until I don't get an exception. The source below will work generally, but be ready to strange and random exceptions, depending on the timing of your program.

Here's the old article: