AutoCAD Event Monitor via COM Interop

A .NET Framework project demonstrating how to expose AutoCAD document events through COM interop and consume them from an external console application.

Overview

This solution consists of two projects:

1. InteropFromAcadAddin - AutoCAD add-in that exposes document events via COM
2. AcadDocEventsTester - Console application that subscribes to and displays AutoCAD events in real-time

Features

• 24 Real-time AutoCAD Events monitored:
  • Document Command Events (Start, End, Cancel, Fail, Unknown)
  • LISP Events (Start, End, Cancel)
  • Document Close Events
  • DocumentManager Events (Created, Activated, Destroyed, Lock Mode changes, etc.)
• Color-coded console output with timestamps
• COM connection point architecture bypassing ServicedComponent transparent proxy issues

Prerequisites

• Visual Studio 2022
• AutoCAD 2024 (or adjust version in code)
• .NET Framework 4.8
• AutoCAD .NET API references

Build Instructions

1. Build the Solution

# Open the solution in Visual Studio
# Build in Debug or Release mode (x64)
# Solution will output to:
# - InteropFromAcadAddin: bin\x64\Debug\InteropFromAcadAddin.dll
# - AcadDocEventsTester: bin\Debug\AcadDocEventsTester.exe

2. Register the AutoCAD Add-in DLL with RegAsm

Open Command Prompt as Administrator and navigate to your AutoCAD 2024 installation directory:

cd "C:\Program Files\Autodesk\AutoCAD 2024"

regasm "<YouPath>\InteropFromAcadAddin\InteropFromAcadAddin\bin\x64\Debug\InteropFromAcadAddin.dll" /codebase /tlb

Note: Adjust paths according to your AutoCAD installation and project location.

3. Add Reference to Console Application (for IntelliSense)

In the AcadDocEventsTester project:

1. Right-click References → Add Reference
2. Click Browse and navigate to:

   <YouPath>\InteropFromAcadAddin\InteropFromAcadAddin\bin\x64\Debug\InteropFromAcadAddin.dll
   

3. Click OK

This provides IntelliSense for the IDocumentEventService and IDocumentEventServiceEvents interfaces.

Running the Event Monitor

Step 1: Load the Add-in in AutoCAD

1. Launch AutoCAD 2024
2. Type NETLOAD at the command prompt
3. Browse to and select:

   <YouPath>\InteropFromAcadAddin\InteropFromAcadAddin\bin\x64\Debug\InteropFromAcadAddin.dll
   

4. The add-in will register itself and start monitoring

Step 2: Run the Console Application

1. Run AcadDocEventsTester.exe (from Visual Studio or directly)
2. The console will connect to the running AutoCAD instance
3. You should see:

   **AutoCAD Event Monitor**
   
   Connected to: AutoCAD 24.3
   Plugin service retrieved successfully.
   
   Service started - now monitoring AutoCAD events.
   
   Event subscription successful!
   
   --- Listening for AutoCAD events ---
   Run commands in AutoCAD to see events here.
   Press ENTER to stop monitoring...
   

Step 3: Watch Events in Real-time

• Execute commands in AutoCAD (LINE, CIRCLE, MOVE, etc.)
• Open/close documents
• Switch between documents
• All events will appear in the console with color-coding and timestamps

Example Output:

[14:23:45.123]  CMD START: 'LINE' | Drawing1.dwg
[14:23:47.456]  CMD END: 'LINE' | Drawing1.dwg
[14:23:50.789]  DOC CREATED | Drawing2.dwg
[14:23:51.012]  DOC BECAME CURRENT | Drawing2.dwg

Step 4: Stop Monitoring

• Press ENTER in the console application to disconnect and exit
• The AutoCAD add-in continues running until AutoCAD closes

Project Structure

InteropFromAcadAddin/
├── InteropFromAcadAddin/           # AutoCAD Add-in Project
│   ├── PluginEntry.cs              # Main COM server + event implementation
│   ├── Properties/AssemblyInfo.cs  # COM visibility settings
│   └── scripts/
│       ├── Register-AcadAddin.bat  # RegAsm registration helper
│       └── Unregister-AcadAddin.bat
│
└── AcadDocEventsTester/            # Console Client Project
    ├── Program.cs                  # COM connection + vtable interop
    └── ComEventSink.cs             # Event sink implementation

Extending Event Coverage

This implementation currently monitors Document and DocumentManager events. You can extend it to include:

• Database Events (ObjectAppended, ObjectModified, ObjectErased, etc.)
• Editor Events (PromptForSelection, etc.)
• Layout Manager Events
• Plot Events
• Application Events

Reference Sample: Check out the comprehensive EventsWatcher sample in the AutoCAD SDK:

<YouPath>\ARX2026\samples\dotNet\EventsWatcher

Troubleshooting

"Failed to retrieve plugin service"

• Ensure the DLL is registered with RegAsm (with /codebase flag)
• Verify the DLL is NETLOAD'ed in AutoCAD

"Unable to cast transparent proxy..."

• This project uses direct vtable calls to bypass ServicedComponent proxy issues
• Ensure you're using the updated Program.cs with FindConnectionPoint, Advise, Unadvise methods

COM Registration Issues

• Always run regasm as Administrator
• Use the /codebase flag to register the DLL location
• Verify bitness matches (x64 AutoCAD requires x64 DLL)

Technical Details

• COM Interface GUIDs:

  • IDocumentEventService: D1C762E4-2C22-482B-9333-82F3E906E6B4
  • IDocumentEventServiceEvents: A7E1B0A4-2E2E-4B6D-9E39-7D6C5B2C9A11
  • PluginEntry CLSID: 75B37C6C-8047-41E3-8C4D-D5196EEFF368

• Architecture:

  • Uses COM connection points for event marshaling
  • Direct vtable calls to bypass .NET Remoting transparent proxies
  • ServicedComponent base class for COM+ compatibility with AutoCAD

License

This is a demonstration project for educational purposes.

Video Demo

Watch the demonstration video showing the event monitor in action:

Demo.mp4

Or download: Demo.mp4

The video demonstrates:

• Loading the AutoCAD add-in with NETLOAD
• Running the console application
• Real-time event monitoring as commands are executed
• Color-coded event output with timestamps
• Document lifecycle events (create, activate, close)

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Note: Paths in this README are examples. Adjust them to match your actual project location and AutoCAD installation directory.