Resolving Assembly Version Conflicts in AutoCAD with AssemblyLoadContext

Problem

When developing AutoCAD .NET plugins, you may encounter assembly version conflicts.
For example:

• AutoCAD ships with System.Configuration.ConfigurationManager version 8.x.
• A third-party plugin or client code wants to use System.Configuration.ConfigurationManager version 9.x for new API features or bug fixes.
• The .NET runtime always prefers the lowest available version in the load context for backward compatibility.
• This means your plugin will end up using AutoCAD’s older 8.x version, even if you package the newer 9.x version — causing missing API members or unexpected behavior.

This is a classic version conflict problem.

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Solution — AssemblyLoadContext

Starting with the .NET Core platform, Microsoft introduced System.Runtime.Loader.AssemblyLoadContext.
It allows you to:

• Load assemblies into isolated contexts separate from the default AppDomain.
• Load a different version of the same assembly without conflicting with AutoCAD’s copy.
• Unload and reload contexts at runtime (useful for hot-reload scenarios).

In this sample, we use AssemblyLoadContext to load ConfigurationManager 9.x in isolation so our plugin can use it without interfering with AutoCAD’s own dependencies.

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How It Works

1. IsolatedContext is created using AssemblyLoadContext.
2. The context explicitly loads:
   • Your target assembly (ConfigurationManager 9.x).
   • Your helper DLL (IsolatedConfigurationManager) that proxies configuration access.
3. All calls to ConfigurationManager go through this isolated helper, ensuring they never resolve to AutoCAD’s 8.x version.
4. You can unload and reload the context during a session for testing.

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Project Structure

Roles:

• Command — Implements the AutoCAD command (TESTEXECONFIG) that triggers the process.
• Interface — Defines common types shared between the AutoCAD host and the isolated loader.
• Isolator — Runs in a separate AssemblyLoadContext to load the desired version of ConfigurationManager.

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Example Config (app.config)

<?xml version="1.0" encoding="utf-8" ?>
<configuration>

    <!-- Application-wide settings -->
    <appSettings>
        <add key="TestKey" value="Hello World" />
        <add key="AnotherKey" value="42" />
        <add key="Environment" value="Development" />
        <add key="FeatureFlag_UseNewUI" value="true" />
    </appSettings>

    <!-- Example connection strings -->
    <connectionStrings>
        <add name="MainDb" connectionString="Server=localhost;Database=MainDB;User Id=testuser;Password=pass123;" providerName="System.Data.SqlClient" />
        <add name="AnalyticsDb" connectionString="Server=analytics.local;Database=Analytics;Integrated Security=True;" providerName="System.Data.SqlClient" />
    </connectionStrings>

    <!-- Example system.web section -->
    <system.web>
        <compilation debug="true" targetFramework="net8.0" />
        <customErrors mode="Off" />
    </system.web>

</configuration>

Building the Plugin

1. Build the solution in Release mode.

2. The output should be arranged into an AutoCAD App Bundle:

Command.bundle
|
PackageContents.xml
│
└───Contents
    │   App.config
    │   Command.deps.json
    │   Command.dll
    │   Command.dll.config
    │   Command.Interface.dll
    │
    └───Isolator
            Command.Interface.dll
            Isolator.deps.json
            Isolator.dll
            Isolator.runtimeconfig.json
            System.Configuration.ConfigurationManager.dll
            System.Diagnostics.EventLog.dll
            System.Diagnostics.EventLog.Messages.dll
            System.Security.Cryptography.ProtectedData.dll

Deploying

1. Copy the Command.bundle folder to:

   %APPDATA%\Autodesk\ApplicationPlugins\

2. Start AutoCAD 2025 or 2026.

AutoCAD will detect and load the plugin automatically.

Running the Demo

In the AutoCAD command line:

Command: TESTEXECONFIG

Expected output:

[AppSetting] TestKey = Hello World
[ConnectionString] MainDb = Server=localhost;Database=MainDB;User Id=testuser;Password=pass123;
[CustomSection] Returned object is null or unexpected type.
Loaded from: D:\Work\Cases\24640596\Command\Bundle\Command.bundle\Contents\Isolator\Isolator.dll

Requirements

• AutoCAD 2025 or 2026 (Windows)

• .NET 8 SDK

• Visual Studio 2022

License

MIT

Written by

Madhukar Moogala (APS , Autodesk)