Cannot Resolve Symbol 'R' Android Studio 3.0

Question

My app was working normally. When I went to sleep I left the PC on and the next morning I found this error in the R: can not resolve symbol ... Try everything, build, even from the gradle and nothing works

When I try to clean up, it throws me a lot of errors, the same is with build and build APK (s)

A big lot of errors

Answer 1

Happened to me too after updating Studio and Gradle version. Even when the problem is in resource files, sometimes it might fail to indicate that. In such a scenario just close the project and import it afresh. That worked for me. The answers and comments in this question provide more details: https://stackoverflow.com/a/49537464/1877184