I imported my Eclipse project into Android using Gradle. At first I had problems with R.java but I resolved them by adding \'gen\' folder as sources in Project Settings.
if you use adb, just restart your device (Phone, Tablet, ...), That works for me.
Check permissions on your SDK directory
You need to run the assemble
task before you can export any apk file.
From the right hand side, open the gradle task
To export debug apk file:
To export release apk file: