OutgoingMessages Property

Collection of outgoing messages with QoS > 0 that have not been fully acknowledged.

Syntax


 getOutgoingMessages(): MQTTMessageList;



Default Value

Remarks

Each time the class publishes a message with a QoS of 1 or 2, it adds it to the OutgoingMessage* properties after the initial PUBLISH packet is sent (this does not occur for messages publish with a QoS of 0). A message remains in the OutgoingMessage* properties until the class has completed all of the acknowledgment steps required for it based on its QoS level.

Outgoing messages with a QoS of 1 follow these steps:

  1. The class sends the PUBLISH packet, then adds the message to OutgoingMessage*.
  2. The class waits to receive a PUBACK (publish acknowledgment) packet.
  3. The MessageAck event is fired.
  4. The message is removed from OutgoingMessage*.
  5. The MessageOut event is fired.

Outgoing messages with a QoS of 2 follow these steps:

  1. The class sends the PUBLISH packet, then adds the message to OutgoingMessage*.
  2. The class waits to receive a PUBREC (publish received) packet.
  3. The class sends a PUBREL (publish release) packet in response.
  4. The class waits to receive a PUBCOMP (publish complete) packet.
  5. The MessageAck event is fired.
  6. The message is removed from OutgoingMessage*.
  7. The MessageOut event is fired.

In MQTT 3.1.1, the RepublishInterval configuration setting, if set to a non-zero value (default), controls how long the class will wait to receive a PUBACK (for QoS 1) or PUBREC (for QoS 2) before automatically republishing an outgoing message. In MQTT 5, messages are only republished if the client is disconnected before receiving a PUBACK or PUBREC.

The class processes messages anytime DoEvents is called. In applications with a GUI, the DoEvents method is also typically called automatically when the class is idle. In all other situations however, it is best practice to call DoEvents in a loop when possible to ensure timely processing of messages.

This property is read-only and not available at design time.

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