Android Studio says some classes have not been used and almost all code is red

Question

I was tweaking the code a little bit, when all of a sudden it looked like this that you can see in the image below. I have no idea what caused it, I tried to do the Clean and the Rebuild and nothing.

Most of these classes that he points to as unused, are being used and where they are used, he turns red giving the Cannot find Symbol. Note that it still compiles and executes the code.

Answer 1

Problem solved! Since the dependencies were already there at Gradle, I had to remove them and re-enter them and do the Sync Project. And so it was successfully corrected!!!