Android Studio “cannot resolve symbol” but project compiles and works

Question

The project compiles fine. However, Android studio 3.0.1 shows reference to one particular library in red and displays \"cannot resolve symbol\". Even single stepping into

Answer 1

I tried Invalidate cache/restart or clean Project -> rebuild project. These didn't work for me.

The final solution was open Project window on the left side of IDE, under Project mode, delete .gradle and .idea folder, then sync, it works.