如何为flutter Mqtt_client设置RETAIN发布消息

Question

现在我可以使用它发布消息

MqttServerClient client = MqttServerClient.withPort(broker, "", 1883); //connect broker

//create message
final builder = MqttClientPayloadBuilder();
builder.addString(message);

client.publishMessage(topic, MqttQos.atLeastOnce, builder.payload); //publish message

但是如何将已发布的消息设置为保留。

Answer 1

根据文档，语法是：

int publishMessage(

    String topic,
    MqttQos qualityOfService,
    Uint8Buffer data,
    {bool retain = false}

) 

所以你的

publish

需要是：

client.publishMessage(topic, MqttQos.atLeastOnce, builder.payload, retain:true);