# .NET Runtime - IExternalCommand Execution

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

![Code Execute Hot Reload](images/RevitDevTool_CodeExecuteHotReload.gif)

---

## 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)

---

## How It Works

### Assembly Loading Process

```mermaid
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]
```

**Similar to RevitAddinManager**, but with automatic detection via FileWatcher.

---

## 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.

---

## 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.

---

## 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.

---

## 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.

---

## 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.

---

## 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

---

## 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)

---

## 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

---

## See Also

- [Python Runtime](CodeExecute-PythonExecution.md) - Python execution with auto-dependencies
- [CodeExecute Overview](CodeExecute-Overview.md) - Module overview
- [vs pyRevit](CodeExecute-VsPyRevit.md) - Python execution comparison