I just read these topics:
Is there a way to get the source code from an APK file?
How to avoid reverse engineering of an APK file?
...and realized that you can't develop an android program without being possible for its .apk file to be reverse engineed. You can use Proguard and tricks but still your code will not be completely hideable.
So if you want to make an app completely close-source what you have to do?
For example, what Facebook and Snapchat and Messenger (e.g) did so their source codes are not accessible?
Also, another question: if you upload your app on google play, then a user can get your .apk?
Thanks in advance!