I wrote this post (in Spanish) a couple of weeks ago as a reminder just in case I have to do something similar in the future. Sometimes I found QT documentation is not all good I would desire and with Android Extras I had to spend quite a lot of time to solve some problems. What I wanted to do is to call Adroid's TexToSpeech class from QT so I used QtAndroidExtras documentation as a reference, this example of notifications and this post of someone else trying to do the same.
Read more: Calling Android's Text to Speech from QT 5.2. An example of QT Android Extras