unsubscribeTopic method
Unsubscribe from a string topic.
Implementation
void unsubscribeTopic(String? topic) {
if (topic == null) {
throw ArgumentError(
'MqttSubscriptionManager::unsubscribeStringTopic - topic is null');
}
final subscriptionTopic = MqttSubscriptionTopic(topic);
final sub = MqttSubscription(subscriptionTopic);
final msgId = messageIdentifierDispenser.nextMessageIdentifier;
final unsubscribeMsg = MqttUnsubscribeMessage()
.withMessageIdentifier(msgId)
.fromStringTopic(topic);
_connectionHandler.sendMessage(unsubscribeMsg);
pendingUnsubscriptions[unsubscribeMsg.variableHeader.messageIdentifier] =
<MqttSubscription>[sub];
}