TsgcWSPClient_MQTT › Events › OnMQTTDisconnect

OnMQTTDisconnect Event

Fires when the broker sends a DISCONNECT or the session is closed; reports ReasonCode and MQTT 5 DisconnectProperties.

Syntax

property OnMQTTDisconnect: TsgcWSMQTTDisconnectEvent;
// TsgcWSMQTTDisconnectEvent = procedure(Connection: TsgcWSConnection; ReasonCode: Integer; const ReasonName: String; DisconnectProperties: TsgcWSMQTTDISCONNECTProperties) of object

Default Value

—

Remarks

Signals that the MQTT session is being terminated. MQTT 3.1.1 has no server-initiated DISCONNECT packet, so in that case the event reflects a locally detected close. MQTT 5.0 introduces a DISCONNECT packet that the broker can send to explain why the connection is being closed. Parameters:

• ReasonCode (MQTT 5) — numeric DISCONNECT reason (0 = Normal disconnection).
• ReasonName (MQTT 5) — human-readable description of ReasonCode.
• DisconnectProperties (MQTT 5) — SessionExpiryInterval, ReasonString, UserProperties and ServerReference (used by the broker to redirect the client to an alternate server).

Use this event to log the cause, update UI state and, if ServerReference is set, consider reconnecting to the suggested broker.

Example

procedure TForm1.MQTTDisconnect(Connection: TsgcWSConnection;
  ReasonCode: Integer; const ReasonName: String;
  DisconnectProperties: TsgcWSMQTTDISCONNECTProperties);
begin
  Memo1.Lines.Add(Format('Disconnect %d (%s)',
    [ReasonCode, ReasonName]));

  if DisconnectProperties.ServerReference <> '' then
    Memo1.Lines.Add('Broker suggests: ' +
      DisconnectProperties.ServerReference);
end;

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