Echelon LNS - Manual (Page 83)

LNS Programmer's Guide 69
an automated installation tool. You could also use it to provide feedback
to a user about the configuration state of devices or routers on your
network. For example, when building a connection, you might want to be
informed of devices that could not be updated. Or, upon receiving a
commission status change event with an “update failed” code, your
application could indicate this by drawing a red circle around the device’s
icon. Later, when the device is reattached to the network and the Object
Server refreshes the device’s network image, your application can remove
the red circle upon receiving a commissioning status change event with
an "update succeeded" code.
• Attach/detach events. The OnAttachment event is generated when the
attachment status of an
AppDevice
or
Router
changes. Once an
application device or router has been commissioned, it can be monitored
via periodic pinging to ensure it is attached. A change in the attachment
status results in this event being generated. Note that the
attachment/detachment events can also be used to monitor the presence
of other remote Full client applications on the network.
• Licensing events. You can use the OnLicenseEvent event to monitor
when the licensing status of the LNS Server changes. This event is
generated upon device crediting, device debiting, deficit credit usage, and
license expiration.
• Missed-event events. The OnMissedEvent event is generated for Full
client applications when one or more events were generated, but not
received by subscribers. For example, missed events could occur while
your application’s Network Service Device is being updated. This event
will contain information about how many events were missed and
whether the missed events are recoverable. You can use the
SetEventSyncMode method to determine whether missed events can be
recovered or not, and you can use the DoEventSync method to maintain
event synchronization in the case of missed events. Consult the LNS
Object Server Reference help file for more information on these methods.
When implementing an event handler for any of the LNS-generated events discussed in
this document, the developer should take into account the following guidelines:
• Each event handler must be implemented as an IDispatch() method
with a valid DISPID. The valid DISPIDs you can use with LNS are
included in the
ConstEventIds
constant. For a complete list, see the
help page for the
ConstEventIds
constant in the LNS Object Server
Reference help file. LNS does not query your event sink object for
DISPIDs by name. This is usually handled automatically by the
application framework (e.g. ATL, MFC, Visual Basic) you are using.
• When not using direct callbacks, your application must service its
Windows Message Queue in order to receive events. In addition to not
receiving events, your application will appear to leak memory while the
queue is not serviced. This is usually only a concern for console or
Windows service applications. For more information on direct callbacks,
see Multi-Threading and LNS Applications on page 318.
• Each event handler should process the event, and return quickly. New
events cannot be processed by a client until the current event handler
returns.