how to get the messageId after the client.publish some msg.

how to get the messageId after the MqttClient.publish some msg.
I don't want to change the MqttClient to MqttAsyncClient with waitForCompletion()
it'll take some time in the thread?
I just publish msg int a thread,and in other thread recieve process the delivered event.
so I want to match the current msg by the messageId

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- [x] Bug exists Release Version 1.2.0 ( Master Branch)
- [ 1] Bug exists in MQTTv3 Client on Snapshot Version 1.2.1-SNAPSHOT (Develop Branch)
- [ ] Bug exists in MQTTv5 Client on Snapshot Version 1.2.1-SNAPSHOT (Develop Branch)

If this is a bug regarding the Android Service, please raise the bug here instead: https://github.com/eclipse/paho.mqtt.android/issues/new