It is now possible to create custom action items in a .NET assembly. This is done by creating a public class that implements the interface ICuiActionCommand (found in MaxCustomControls.dll) and placing the DLL containing the implemented interface in the bin\assemblies folder. 3ds Max will then dynamically load an instance of this class as an action in its CUI interface. When the action is executed by 3ds Max the method ICommand.Execute() will be called on the loaded class.

To simplify the construction of .NET custom actions, a custom class can inherit from the abstract base class CuiActionCommandAdapter. For more information see the .NET reference guide.