Android Studio unresolved reference. Project compiles

Question

After upgrading Android Studio, a project with no issues started showing issues in the editor. I have lots of Unresolved Reference errors. Anything under the su

Answer 1

I agree with Stanislav Mukhametshin that may be it is related with new AndroidX libraries and migration on it. I had cleaned and rebuilt project but that didn't work. So, I tried this way and error goes away.

1) Go to File and close project.

2) Reopen the same project.