3.4.5. DataReaderListener

DataReaderListener is an abstract class defining the callbacks that will be triggered in response to state changes on the DataReader. By default, all these callbacks are empty and do nothing. The user should implement a specialization of this class overriding the callbacks that are needed on the application. Callbacks that are not overridden will maintain their empty implementation.

DataReaderListener defines the following callbacks:

• on_data_available(): There is new data available for the application on the DataReader. There is no queuing of invocations to this callback, meaning that if several new data changes are received at once, only one callback invocation may be issued for all of them, instead of one per change. If the application is retrieving the received data on this callback, it must keep reading data until no new changes are left.

• on_subscription_matched(): The DataReader has found a DataWriter that matches the Topic and has a common partition and a compatible QoS, or has ceased to be matched with a DataWriter that was previously considered to be matched. It is also triggered when a matched DataWriter has changed its DataWriterQos.

• on_requested_deadline_missed(): The DataReader did not receive data within the deadline period configured on its DataReaderQos. It will be called for each deadline period and data instance for which the DataReader missed data.

Warning

Currently on_requested_deadline_missed() is not implemented (it will never be called), and will be implemented on a future release of Fast DDS.

• on_requested_incompatible_qos(): The DataReader has found a DataWriter that matches the Topic and has a common partition, but with a QoS that is incompatible with the one defined on the DataReader.

• on_liveliness_changed(): The liveliness status of a matched DataWriter has changed. Either a DataWriter that was inactive has become active or the other way around.

• on_sample_rejected(): A received data sample was rejected. See SampleRejectedStatus for further information.

• on_sample_lost(): A data sample was lost and will never be received. See SampleLostStatus for further information.

Important

For more information about callbacks and its hierarchy, please refer to Listener.

class CustomDataReaderListener : public DataReaderListener
{

public:

    CustomDataReaderListener()
        : DataReaderListener()
    {
    }

    virtual ~CustomDataReaderListener()
    {
    }

    virtual void on_data_available(
            DataReader* reader)
    {
        (void)reader;
        std::cout << "Received new data message" << std::endl;
    }

    virtual void on_subscription_matched(
            DataReader* reader,
            const SubscriptionMatchedStatus& info)
    {
        (void)reader;
        if (info.current_count_change == 1)
        {
            std::cout << "Matched a remote DataWriter" << std::endl;
        }
        else if (info.current_count_change == -1)
        {
            std::cout << "Unmatched a remote DataWriter" << std::endl;
        }
    }

    virtual void on_requested_deadline_missed(
            DataReader* reader,
            const eprosima::fastrtps::RequestedDeadlineMissedStatus& info)
    {
        (void)reader, (void)info;
        std::cout << "Some data was not received on time" << std::endl;
    }

    virtual void on_liveliness_changed(
            DataReader* reader,
            const eprosima::fastrtps::LivelinessChangedStatus& info)
    {
        (void)reader;
        if (info.alive_count_change == 1)
        {
            std::cout << "A matched DataWriter has become active" << std::endl;
        }
        else if (info.not_alive_count_change == 1)
        {
            std::cout << "A matched DataWriter has become inactive" << std::endl;
        }
    }

    virtual void on_sample_rejected(
            DataReader* reader,
            const eprosima::fastrtps::SampleRejectedStatus& info)
    {
        (void)reader, (void)info;
        std::cout << "A received data sample was rejected" << std::endl;
    }

    virtual void on_requested_incompatible_qos(
            DataReader* /*reader*/,
            const RequestedIncompatibleQosStatus& info)
    {
        std::cout << "Found a remote Topic with incompatible QoS (QoS ID: " << info.last_policy_id <<
            ")" << std::endl;
    }

    virtual void on_sample_lost(
            DataReader* reader,
            const SampleLostStatus& info)
    {
        (void)reader, (void)info;
        std::cout << "A data sample was lost and will not be received" << std::endl;
    }

};