Echelon LNS - Manual (Page 296)

LNS Programmer's Guide 282
This will release the reference to the plug-in, and will therefore stop the director from
accessing the plug-in application’s properties and methods through the MyPlugIn
variable. However, releasing the reference will not terminate the plug-in itself. The LNS
Plug-In Programmer’s Guide contains a section called How Plug-Ins Know When To Exit
that addresses the plug-in lifetime considerations for the plug-in developer.
The director application is free to hold on to the reference. This will allow you to speed up
processing during the network commissioning phase, as plug-ins that are invisible but
attached do not need be re-loaded into memory. Therefore, the director can provide a very
responsive user-interface.
However, Echelon recommends that you release plug-in references using a timer-
controlled scheme to avoid blocking system resources with plug-ins. For example, the
director application could automatically release references to a plug-in 15 minutes after
the last use of that plug-in, and restart the timer each time the user demands the
services of that plug-in.
A complete example implementation of the client-side plug-in API is contained in the
example director application described in Appendix C of this document. The related
source code can be found in the Launch() method that is contained in the cCommand
class.
Detecting Existing Plug-Ins
Before you can use a plug-in to perform its prime service such as configuring a particular
implementation of a device, the plug-in must be fully registered within the Windows
operating system, and the LNS system. The LNS Plug-In Programmer’s Guide provides a
discussion of the plug-in registration process. This section provides a brief overview of
the process, focusing on the director’s role in plug-in registration.
When LNS plug-in software is installed, the installation includes registration of the plug-
in application’s COM server with the Windows Registry. Among other details, this
publishes the plug-in application’s Registered Server Name to the Windows system. At
the same time, the plug-in registers with an LNS-specific part of the Windows Registry,
by adding or updating data under the
HKEY_LOCAL_MACHINE\SOFTWARE\LonWorks\LCA\Plug-Ins key. The director detects
all subkeys stored under HKEY_LOCAL_MACHINE\SOFTWARE\LonWorks\LCA\Plug-Ins
in the Windows Registry. Each subkey relates to an LNS plug-in application. Following
is an example screenshot, showing the Plug-In Windows Registry key explored in the
Windows RegEdit.exe utility, highlighting the Echelon LNS Report Generator plug-in: