registerDomain
registerDomain — registers to receive updates from domain points.
ST_STATUS registerDomain( | domainname, | |
flags); |
LPCTSTR domainname;int flags;Exception registerDomain( | domainname, | |
flags); |
String domainname;int flags;domainnameThe name of a domain.
flagsSpecifies conditions and actions associated with registering the domain points, as follows (flags may be combined):
DHC_FLAG_REG_FUTURE: points created
in the future are also affected. If not set, then only those
points existing (in the domain) at the time the command
message is received by the DataHub instance are
registered.
DHC_FLAG_REG_QUALIFY: point names are
to be transmitted with the domain name prepended to the
point name, as
domainname:pointname
DHC_FLAG_REG_ONCEONLY: the point
values are transmitted only once, and the points remain
unregistered. This mode is useful for obtaining an initial
list of available points from which a selection is made of
which ones to register.
ST_OK if the command was successfully sent to the
DataHub instance. Since the command is sent asynchronously, the actual
success or failure of the command must be determined through the onSuccess
or onError message handlers.
ST_NO_TASK if a connection to the DataHub instance
does not exist.
ST_ERROR if the connection socket is unable to
send the message.
This method registers the client to receive updates from the DataHub instance
when the value of any points in the specified domain change. The
onPointChange method is called for each
point update received. The registerDomain method may be
called more than once, and on different domains.
Upon registering the domain, all points currently in that domain of the DataHub
instance are immediately transmitted to the client. Points that are subsequently
created will only be sent if the DHC_FLAG_REG_FUTURE flag
is specified. The DHC_FLAG_REG_QUALIFY flag is useful for
distinguishing points from different domains that have the same name.
In a typical scenario, either there is no need to register for all points, or
the point names are not even known. In either case, you can use the
DHC_FLAG_REG_ONCEONLY flag to generate an initial list
of all available points in the specified domain. Then you can call
registerPoint on any points of interest, as
they are received in
onPointChange.