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All Atlas MQTT components · Atlas MQTT guide

TAtlasMqttMessageEvent

The type of TAtlasMqttClient.OnMessage: one delivered message.

Type Unit Atlas.MqttClient · Product Atlas MQTT

Description

pascal
TAtlasMqttMessageEvent = procedure(Sender: TObject; const Topic: string; const Payload: TBytes;
  QoS: TMqttQoS; Retained: Boolean) of object;

Sender is the client. Topic is the topic the message was published to, never a filter. Payload holds the raw bytes; decode text with TEncoding.UTF8.GetString. QoS is the quality it was delivered at. Retained is True when the broker replays a retained message to a new subscription. The handler runs on the main thread, or on the client's thread when SynchronizeEvents is False.

This type has no members of its own beyond those listed in its description.

Examples

Parse a temperature

A handler that keeps the latest reading from any topic ending in /temperature.

pascal
uses
  System.SysUtils, Atlas.MqttCodec, Atlas.MqttClient;

type
  TTemperatureView = class
    Celsius: Double;
    procedure ClientMessage(Sender: TObject; const Topic: string; const Payload: TBytes;
      QoS: TMqttQoS; Retained: Boolean);
  end;

procedure TTemperatureView.ClientMessage(Sender: TObject; const Topic: string; const Payload: TBytes;
  QoS: TMqttQoS; Retained: Boolean);
begin
  if Topic.EndsWith('/temperature') then
    Celsius := StrToFloat(TEncoding.UTF8.GetString(Payload), TFormatSettings.Invariant);
end;

procedure AttachView(Client: TAtlasMqttClient; View: TTemperatureView);
begin
  Client.OnMessage := View.ClientMessage;
end;

TAtlasMqttClient · TMqttQoS

Also in Atlas MQTT

TAtlasMqttClient · TAtlasMqttBroker