Echelon OpenLDV User Manual download pdf (Page 99)

OpenLDV Programmer’s Guide 91

NiSendImmediate(), NiGetNextResponse(), NiSendResponse(), NiClose(),

and NiEncryption().

The OpenLDVni.h header file contains details about this class and its usage.

The COpenLDVni class also implements and controls a worker thread,

COpenLDVmessagePump. This thread operates as a message pump, receiving

and dispatching uplink messages from the COpenLDVapi class.

To dispatch an incoming message, a message dispatcher decodes the message,

takes appropriate action local to the OpenLDV application, and responds

accordingly to the network. For example, the incoming message might describe

an update to an input network variable. The message dispatcher for the

application receiving this message must recognize the message as a network-

variable update message, and route the new network-variable data to the

relevant application storage. Other message types might also cause interaction

with the network. For example, the application might receive a network-variable

fetch message. In this case, the dispatcher must obtain the current value of the

network variable in question, and report the value to the network by constructing

an appropriate response message.

The message pump thread in this example application uses the functions

provided by the COpenLDVni and COpenLDVapi classes to retrieve and

dispatch messages. These messages are sent using an NiDispatch method. The

COpenLDVni class specifies, but does not implement, such a NiDispatch

method. Therefore, the COpenLDVni class is an abstract C++ class.

The OpenLDV Developer Example implements an example for an application-

specific message dispatcher (COpenLDVexampleDispatcher), derived from

the COpenLDVni class, which implements the NiDispatch method.

The example dispatcher implements handlers for a variety of messages, including

handlers for selected network management and diagnostics messages such as

HandleQuerySnvt, HandleSetNodeMode, or HandleServicePin.

You can use the COpenLDVexampleDispatcher class as an example for your

OpenLDV application, but you must adapt and rewrite the dispatcher for the

application.

The OpenLDVexampleDispatcher.h header file and the

OpenLDVexampleDispatcher.cpp implementation file contain comments

that describe the details of the implementation.

Toolkits and User Interface

The OpenLDV Developer Example provides a simple user interface based on a

single dialog. The OpenLDV ExampleDlg.cpp implementation file contains

event handlers related to that user interface, such as the various click-event

handlers related to buttons. The same COpenLDV ExampleDlg class also

provides example instantiation of the above classes.

For most operations, however, the dialog uses the COpenLDVtools class as a

toolkit. This class provides a simple interface that implements selected

operations such as QueryDomain, LeaveDomain, or UpdateDomain. The

COpenLDvtools class also implements a FindDevices() function that

demonstrates the implementation of multi-transaction sequences within the

context of this framework.

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