Unlike other AutoCAD reactors, object reactors are attached to specific AutoCAD entities (objects).
When you define an object reactor, you must identify the entity to which the reactor is to be attached. The vlr-object-reactor function, which creates object reactors, requires the following arguments:
For example, the following statement defines an object reactor with a single owner (the object identified by myCircle), then attaches the string “Circle Reactor” to the reactor and tells AutoCAD to invoke the print-radius function when a user modifies myCircle:
(setq circleReactor (vlr-object-reactor (list myCircle) "Circle Reactor" '((:vlr-modified . print-radius))))
The reactor object is stored in variable circleReactor; you can refer to the reactor using this variable. When defining a list of owners, you must specify VLA-objects only; Ename objects are not allowed. VLA-objects are required because callback functions can only use ActiveX methods to modify AutoCAD objects, and ActiveX methods require a VLA-object to work on. You can convert these Ename objects into VLA-objects using the vlax-ename->vla-object function.
You do not have to specify any data to be included with the reactor; you can specify nil instead. However, an object may have several reactors attached to it. You can include an identifying text string, or other data your application can use, to allow you to distinguish among the different reactors attached to an object.