Rhino plug-ins can contain any number of commands. Commands are created by deriving a new classes from CRhinoCommand, or MRhinoCommand in .NET. See rhinoSdkCommand.h for details on the CRhinoCommand class.

The following example code demonstrates a simple command class that essentially does nothing.

// Do NOT put the definition of class CCommandTest in a header
// file.  There is only ONE instance of a CCommandTest class
// and that instance is the static theTestCommand that appears
// immediately below the class definition.
 
class CCommandTest : public CRhinoCommand
{
public:
  // The one and only instance of CCommandTest is created below.
  // No copy constructor or operator= is required.  Values of
  // member variables persist for the duration of the application.
 
  // CCommandTest::CCommandTest()
  // is called exactly once when static theTestCommand is created.
  CCommandTest() {}
 
  // CCommandTest::~CCommandTest()
  // is called exactly once when static theTestCommand is
  // destroyed.  The destructor should not make any calls to
  // the Rhino SDK.  If your command has persistent settings,
  // then override CRhinoCommand::SaveProfile and CRhinoCommand::LoadProfile.
  ~CCommandTest() {}
 
  // Returns a unique UUID for this command.
  // If you try to use an id that is already being used, then
  // your command will not work.  Use GUIDGEN.EXE to make unique UUID.
  UUID CommandUUID()
  {
    // {5333C9DE-5F01-45B8-9154-28B765E453E0}
    static const GUID TestCommand_UUID =
    { 0x5333C9DE, 0x5F01, 0x45B8, { 0x91, 0x54, 0x28, 0xB7, 0x65, 0xE4, 0x53, 0xE0 } };
    return TestCommand_UUID;
  }
 
  // Returns the English command name.
  const wchar_t* EnglishCommandName() { return L"Test"; }
 
  // Returns the localized command name.
  const wchar_t* LocalCommandName() { return L"Test"; }
 
  // Rhino calls RunCommand to run the command.
  CRhinoCommand::result RunCommand( const CRhinoCommandContext& );
};
 
// The one and only CCommandTest object.  
// Do NOT create any other instance of a CCommandTest class.
static class CCommandTest theTestCommand;
 
CRhinoCommand::result CCommandTest::RunCommand( const CRhinoCommandContext& context )
{
  // CCommandTest::RunCommand() is called when the user runs the "Test"
  // command or the "Test" command is run by a history operation.
 
  // TODO: Add command code here.
 
  // Rhino command that display a dialog box interface should also support
  // a command-line, or scriptable interface.
 
  ON_wString wStr;
  wStr.Format( L"The \"%s\" command is under construction.\n", EnglishCommandName() );
  if( context.IsInteractive() )
    RhinoMessageBox( wStr, PlugIn()->PlugInName(), MB_OK );
  else
    RhinoApp().Print( wStr );
 
  // TODO: Return one of the following values:
  //   CRhinoCommand::success:  The command worked.
  //   CRhinoCommand::failure:  The command failed because of invalid input, inability
  //                            to compute the desired result, or some other reason
  //                            computation reason.
  //   CRhinoCommand::cancel:   The user interactively canceled the command 
  //                            (by pressing ESCAPE, clicking a CANCEL button, etc.)
  //                            in a Get operation, dialog, time consuming computation, etc.
  //   CRhinoCommand::nothing:  The command did nothing but CANCEL was not pressed.
 
  return CHippoCommand::success;
}

1. Command classes must return a unique UUID. If you try to use a UUID that is already in use, then your command will not work. Use the GUIDGEN.EXE that comes with Visual Studio to create unique UUIDs.
2. Command classes must return a unique command name. If you try to use a command name that is already in use, then your command will not work.
3. Only ONE instance of a command class can be created. This is why you should put the definition of your command classes in .cpp files.

The Rhino Command Generator wizard is a standalone application that will generate new skeleton CRhinoCommand-derived class. The generated source code is copied to the Windows clipboard so you can easily paste it into your source files. Note, this tool can be used for both Rhino 3.0 and Rhino 4.0 development.

To use this tool in Visual Studio 2005:

1. Launch Visual Studio 2005.
2. Select Tools→External Tools…
3. Use the Add button to add the RhinoCommandGenerator.exe file to the list. This file can be found in C:\Program Files\Rhino 4.0 SDK\CmdWizard.

Rules to follow when deriving new command classes.

1. Command classes must return a unique UUID. If you try to use a UUID that is already in use, then your command will not work. Use the GUIDGEN.EXE that comes with Visual Studio to create unique UUIDs. If you are using one of the Express Editions of Visual Studio, GUIDGEN.EXE is located in the ..\Common7\Tools directory of your Visual Studio installation. Use the Tools menu to add this executable as an external tool.
2. Command classes must return a unique command name. If you try to use a command name that is already in use, then your command will not work.
3. Only ONE instance of a command class can be created. You should NEVER create an instance of your command class. Rhino will use reflection to inspect your assembly and create an instance of your command class at the appropriate time. This also means that your command classes must be declared public so they can be seen through Reflection.

The VB.NET and C# wizards contain command wizards. On the menu click “Project” and then “Add New Item”. Select the “Rhino Command” item and type in a name that you would like your command to have. The wizard will add a new command class to your project and generate a new UUID for that class.