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

This has happened to me a couple of times, there are a few ways you can resolve this problem;

1. Sync project files with gradle in the File toolbar
2. Use the Invalidate/Restart option in the File toolbar to invalidate the caches.
3. Delete the .idea folder and restart Android Studio