Listeners

Concept

The Listener class is the abstract base class for all listeners. Each entity class (DomainParticipant, Topic, Publisher, DataWriter, Subscriber, and DataReader) has its own derived Listener class that add methods for handling entity-specific statuses. The methods are called by an internal Connext DDS thread when the corresponding status for the Entity changes value.

You can choose which changes in status will trigger a callback by installing a listener with a bit mask. Bits in the mask correspond to different statuses. The bits that are true indicate that the listener will be called back when there are changes in the corresponding status. You can specify a listener and set its bit-mask before or after you create an Entity:

DDS_StatusMask mask = DDS_REQUESTED_DEADLINE_MISSED_STATUS
        | DDS_DATA_AVAILABLE_STATUS;
datareader = subscriber->create_datareader(
        topic, 
        DDS_DATAREADER_QOS_DEFAULT,
        listener, 
        mask); 

DDS_StatusMask mask = DDS_REQUESTED_DEADLINE_MISSED_STATUS
        | DDS_DATA_AVAILABLE_STATUS; 

datareader->set_listener(listener, mask);

Example Description

This example shows how to define listeners for different entity classes, adding methods for handling entity-specific statuses.

In the publisher application we create a Data Writer listener class that prints out messages every time an event is triggered. We also create an inconsistent topic so the reader's handler gets called.

In the subscriber application we implement three listeners for Participant, Subscriber, and DataReader, respectively.

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