CodeExecute DotNetExecution

.NET Runtime - IExternalCommand Execution

RevitDevTool executes .NET assemblies using the same approach as RevitAddinManager, with a few focused improvements.

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Philosophy

RevitDevTool's C# support is inspired by RevitAddinManager:

• Load IExternalCommand implementations dynamically
• Execute without Revit restart
• Enable rapid development iteration

Key additions:

1. FileWatcher for automatic command detection
2. Automatic dependency loading
3. No temp folder copy for Revit 2024- (.NET 4.8)

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How It Works

Assembly Loading Process

flowchart TD
    A[Developer builds DLL] --> B[RevitDevTool discovers<br/>IExternalCommand implementations]
    B --> C[FileWatcher detects<br/>new commands automatically]
    C --> D[Load assembly<br/>with all dependencies]
    D --> E[User clicks command]
    E --> F[Execute]

Loading

Similar to RevitAddinManager, but with automatic detection via FileWatcher.

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Revit Version Differences

Revit 2024 and Earlier (.NET Framework 4.8)

RevitAddinManager approach:

• Copy DLL to temp folder
• Load from temp location
• Execute

RevitDevTool approach:

• Load DLL directly (no temp folder)
• Execute

Advantage: Faster loading, simpler debugging paths.

Revit 2025+ (.NET 8.0)

Both tools use the same approach:

• Use AssemblyLoadContext (ALC)
• Load in-memory
• Execute

No difference - both leverage .NET 8.0's AssemblyLoadContext for proper isolation.

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Key Improvements Over RevitAddinManager

1. FileWatcher for New Commands

When you add a new IExternalCommand to your DLL and rebuild:

• RevitAddinManager: Requires manual reload
• RevitDevTool: FileWatcher detects automatically, command appears

Benefit: One less manual step in the development loop.

2. Automatic Dependency Loading

All DLLs in the folder are loaded automatically:

• NuGet packages (Newtonsoft.Json, Serilog, etc.)
• Project references
• Third-party libraries

Benefit: No configuration needed for dependencies.

3. No Temp Folder (Revit 2024-)

For .NET Framework 4.8 (Revit 2024 and earlier):

• No copy step
• Faster execution
• Simpler debugging (no temp folder paths)

Note: This advantage only applies to Revit 2024 and earlier. Revit 2025+ uses AssemblyLoadContext for both tools.

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Command Discovery

RevitDevTool scans assemblies for types that implement IExternalCommand:

• Finds all public classes implementing IExternalCommand
• Creates tree nodes for UI display
• Organizes by namespace hierarchy

Same as RevitAddinManager - uses standard .NET reflection.

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Command Execution

When user clicks a command:

1. Create instance of IExternalCommand class
2. Call Execute method with Revit context
3. Capture output to Trace panel

Same as RevitAddinManager - uses standard IExternalCommand interface.

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FileWatcher Implementation

FileWatcher monitors the assembly folder for changes:

• Detects when DLL files are modified
• Automatically reloads assemblies
• Updates UI tree with new commands

Benefit: New commands appear without manual reload.

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Developer Workflow

With RevitDevTool

1. Edit C# code
2. Build project
3. FileWatcher detects changes automatically
4. New commands appear in UI
5. Test changes

With RevitAddinManager

1. Edit C# code
2. Build project
3. Manually reload add-in
4. New commands appear in UI
5. Test changes

Difference: Step 3 is automatic in RevitDevTool.

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What RevitDevTool Does NOT Do

RevitDevTool is not:

• ❌ A hot reload system (no in-memory code updates)
• ❌ A replacement for Visual Studio debugging
• ❌ A build system

RevitDevTool is:

• ✅ An execution engine for IExternalCommand
• ✅ A FileWatcher for automatic command detection
• ✅ A dependency loader

For actual debugging: Use Visual Studio's "Attach to Process" feature.

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Comparison with RevitAddinManager

Feature	RevitAddinManager	RevitDevTool
Load IExternalCommand	✅	✅
Execute without restart	✅	✅
FileWatcher for new commands	❌ Manual reload	✅ Automatic
Dependency loading	⚠️ Manual config	✅ Automatic
Temp folder (Revit 2024-)	✅ Uses temp folder	❌ Direct load
Temp folder (Revit 2025+)	❌ ALC in-memory	❌ ALC in-memory
UI complexity	Full-featured	Minimal
Configuration	Extensive	Minimal

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When to Use RevitDevTool for C#

Good for:

• ✅ Rapid iteration with automatic command detection
• ✅ Simple execution without configuration
• ✅ Revit 2024- development (no temp folder)
• ✅ Projects with many dependencies (auto-loaded)

Not ideal for:

• ❌ Complex add-in management needs
• ❌ When you need RevitAddinManager-specific features
• ❌ When you prefer manual control over loading

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Limitations

Same limitations as RevitAddinManager:

• Cannot modify loaded assemblies without rebuild
• Cannot change type definitions at runtime
• Requires Visual Studio for debugging

Additional notes:

• FileWatcher may have slight delay (typically <1 second)
• All DLLs loaded automatically (may load unnecessary files)

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Summary

RevitDevTool's C# support:

• Inspired by RevitAddinManager's proven approach
• Adds FileWatcher for automatic command detection
• Adds automatic dependency loading
• Removes temp folder copy for Revit 2024- (.NET 4.8)
• Simplifies interface by removing unnecessary features

Not a replacement, but a focused alternative for developers who want:

• Automatic command detection
• Automatic dependency loading
• Simpler workflow

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See Also

• Python Runtime - Python execution with auto-dependencies
• CodeExecute Overview - Module overview
• vs pyRevit - Python execution comparison