So I added this functionality of reading filesystem. When I debugged it on my android, there was a NullPointerException, so after some googling (on StackOverflow) I found that I need to add permission to the manifest file. After doing this, I rebuilt it many times, but it seems that after running it on my phone, it was not properly updated, because the NPE persisted. that's why I decided to manually (using Samsung's option ) uninstall it, hoping it will be reinstalled by Android Studio.
Sadly after that action, I cannot run this application anymore.
Default Activity not found
I don't see this application in apps list neither in main menu. I tried also
adb install ...pathtoapk...
But it says it is already installed
adb -r install ...pathtoapk...
Also does not work, says it is installed correctly, but app is still not visible neither in menu nor app list