Android Studio don't generate R.java for my import project

Question

I import a project to Android Studio , but the R.java is always empty.

public final class R {
}

I have tried:

1. Make project,ma

Answer 1

When I was trying to add another flavour I face same situation.

I found in one of post and I gave successful try and it work. Following I did: File -> Invalidate Cached/Restart.