Error running 'app': Unknown error in Android studio 3.1
问题 I have updated my android studio to new stable version 3.1 . After build project not able to run. Let me know if anyone have face same issue or find any solution. 回答1: Just go to " Run/edit configurations... /" and scroll down to bottom of the window and here you see an option " Before launch... " First, remove whatever already inside the little window and then click on ( + ) icon and select "Gradle-aware Make " and then type " assembleDebug " and select the first option or that you need.