As stated in DomainParticipantListener, the DomainParticipantListener is an abstract class defining the callbacks that will be triggered in response to state changes on the DomainParticipant. Fast DDS defines three callbacks attached to events tha...-DPDK中文网

The provided code snippet demonstrates how to implement a custom listener for the Fast DDS (Fast Data Distribution Service) DomainParticipant. The DiscoveryDomainParticipantListener class extends the abstract DomainParticipantListener class, which allows you to define callback functions that respond to various discovery events in the DDS environment.

Overview of Callbacks

on_participant_discovery: This callback is triggered when a DomainParticipant is discovered, its QoS changes, or it leaves the domain.
- DISCOVERED_PARTICIPANT: Handles new participants joining.
- CHANGED_QOS_PARTICIPANT: Can be used to react if an existing participant changes its Quality of Service settings.
- REMOVED_PARTICIPANT: Reacts when a participant leaves the domain.
on_data_reader_discovery: This callback is invoked for data readers.
- DISCOVERED_READER: Indicates a new data reader has been found.
- CHANGED_QOS_READER: Triggered if an existing data reader changes its QoS.
- REMOVED_READER: Occurs when a data reader leaves the domain.
on_data_writer_discovery: This callback is called for data writers.
- DISCOVERED_WRITER: New data writer found in the system.
- CHANGED_QOS_WRITER: For any QoS change on existing writers.
- REMOVED_WRITER: When a writer is no longer available in the domain.

Implementation Steps

Create and define your own listener class (DiscoveryDomainParticipantListener) that overrides these methods according to your needs.
Inside each method, you can add custom logic based on your application requirements—such as logging information about discovered entities or deciding whether they should be ignored using the should_be_ignored parameter.
To use this listener, instantiate it and register it with your DomainParticipant during its creation:

// Create the participant QoS and configure values
DomainParticipantQos pqos;

// Create a custom user DomainParticipantListener
DiscoveryDomainParticipantListener* plistener = new DiscoveryDomainParticipantListener();

// Pass the listener on DomainParticipant creation
DomainParticipant* participant =
        DomainParticipantFactory::get_instance()->create_participant(
    0, pqos, plistener);

Important Notes

Make sure to manage memory correctly since you’re allocating plistener with new. Depending on your architecture, consider using smart pointers like std::shared_ptr or std::unique_ptr.
Properly handle scenarios where participants may join or leave dynamically; keeping track of state will be crucial for robust applications utilizing DDS.
Further details regarding callbacks and their hierarchy can typically be found in the official documentation or specific sections related to event handling within Fast DDS.

This pattern allows applications built on Fast DDS to respond efficiently to dynamic network environments by tracking and reacting to entity states effectively.

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