Out-of-Process Versus In-Process (.NET)

When you develop a new application, it can either run in or out-of-process. The AutoCAD .NET API is designed to run in-process only, which is different from the ActiveX Automation library which can be used in or -out-of-process.

• In-process applications are designed to run in the same process space as the host application. In this case, a DLL assembly is loaded into AutoCAD which is the host application.
• Out-of-process applications do not run in the same space as the host application. These applications are often built as stand-alone executables.

If you need to create a stand-alone application to drive AutoCAD, it is best to create an application that uses the CreateObject and GetObject methods to create a new instance of an AutoCAD application or return one of the instances that is currently running. Once a reference to an AcadApplication is returned, you can then load your in-process .NET application into AutoCAD by using the SendCommand method that is a member of the ActiveDocument property of the AcadApplication.

As an alternative to executing your .NET application in-process, could use COM interop for your application.

Note: The ProgID for COM application access to AutoCAD 2021 is AutoCAD.Application.24.

VB.NET

Imports System
Imports System.Runtime.InteropServices
 
Imports Autodesk.AutoCAD.Interop
Imports Autodesk.AutoCAD.Runtime
Imports Autodesk.AutoCAD.ApplicationServices
 
<CommandMethod("ConnectToAcad")> _
Public Sub ConnectToAcad()
  Dim acAppComObj As AcadApplication
  Dim strProgId As String = "AutoCAD.Application.24"
 
  On Error Resume Next
 
  '' Get a running instance of AutoCAD
  acAppComObj = GetObject(, strProgId)
 
  '' An error occurs if no instance is running
  If Err.Number > 0 Then
      Err.Clear()
 
      '' Create a new instance of AutoCAD
      acAppComObj = CreateObject(strProgId)
 
      '' Check to see if an instance of AutoCAD was created
      If Err.Number > 0 Then
         Err.Clear()
 
         '' If an instance of AutoCAD is not created then message and exit
         MsgBox("Instance of 'AutoCAD.Application' could not be created.")
 
         Exit Sub
      End If
  End If
 
  '' Display the application and return the name and version
  acAppComObj.Visible = True
  MsgBox("Now running " & acAppComObj.Name & " version " & acAppComObj.Version)
 
  '' Get the active document
  Dim acDocComObj As AcadDocument
  acDocComObj = acAppComObj.ActiveDocument
 
  '' Optionally, load your assembly and start your command or if your assembly
  '' is demandloaded, simply start the command of your in-process assembly.
  acDocComObj.SendCommand("(command " & Chr(34) & "NETLOAD" & Chr(34) & " " & _
                          Chr(34) & "c:/myapps/mycommands.dll" & Chr(34) & ") ")
 
  acDocComObj.SendCommand("MyCommand ")
End Sub

C#

using System;
using System.Runtime.InteropServices;
 
using Autodesk.AutoCAD.Interop;
using Autodesk.AutoCAD.Runtime;
using Autodesk.AutoCAD.ApplicationServices;
 
[CommandMethod("ConnectToAcad")]
public static void ConnectToAcad()
{
 
  AcadApplication acAppComObj = null;
  const string strProgId = "AutoCAD.Application.24";
 
  // Get a running instance of AutoCAD
  try
  {
      acAppComObj = (AcadApplication)Marshal.GetActiveObject(strProgId);
  }
  catch // An error occurs if no instance is running
  {
      try
      {
          // Create a new instance of AutoCAD
          acAppComObj = (AcadApplication)Activator.CreateInstance(Type.GetTypeFromProgID(strProgId), true);
      }
      catch
      {
          // If an instance of AutoCAD is not created then message and exit
          System.Windows.Forms.MessageBox.Show("Instance of 'AutoCAD.Application'" +
                                               " could not be created.");
 
          return;
      }
  }
 
  // Display the application and return the name and version
  acAppComObj.Visible = true;
  System.Windows.Forms.MessageBox.Show("Now running " + acAppComObj.Name + 
                                       " version " + acAppComObj.Version);
 
  // Get the active document
  AcadDocument acDocComObj;
  acDocComObj = acAppComObj.ActiveDocument;
 
  // Optionally, load your assembly and start your command or if your assembly
  // is demandloaded, simply start the command of your in-process assembly.
  acDocComObj.SendCommand("(command " + (char)34 + "NETLOAD" + (char)34 + " " +
                          (char)34 + "c:/myapps/mycommands.dll" + (char)34 + ") ");
 
  acDocComObj.SendCommand("MyCommand ");
}

VBA/ActiveX Code Reference

Sub ConnectToAcad()
    Dim acadApp As AcadApplication
    On Error Resume Next
 
    Set acadApp = GetObject(, "AutoCAD.Application.24")
    If Err Then
        Err.Clear
        Set acadApp = CreateObject("AutoCAD.Application.24")
        If Err Then
            MsgBox Err.Description
            Exit Sub
        End If
    End If
 
    acadApp.Visible = True
    MsgBox "Now running " + acadApp.Name + _
           " version " + acadApp.Version
 
    Dim acadDoc as AcadDocument
    Set acadDoc = acadApp.ActiveDocument
 
    '' Optionally, load your assembly and start your command or if your assembly
    '' is demandloaded, simply start the command of your in-process assembly.
    acadDoc.SendCommand("(command " & Chr(34) & "NETLOAD" & Chr(34) & " " & _
                        Chr(34) & "c:/myapps/mycommands.dll" & Chr(34) & ") ")
 
    acadDoc.SendCommand("MyCommand ")
End Sub