The process of passing messages between AutoCAD and the ObjectARX application flows almost completely in one direction—from AutoCAD to the ObjectARX application. The following diagram shows a typical sequence for passing messages.
If an application is loaded when a drawing is already open, the kInitAppMsg and kLoadDwgMsg messages are sent in succession. When an ObjectARX application is unloaded while an edit session is in progress, the kUnloadDwg and kUnloadApp messages are sent in succession.