Error inflating class android.support.design.widget.CoordinatorLayout

Please change it into AppCompatActivity if you use Activity. Probably it becomes the error when it is Activity.

Just use this line in FloatingActionButton (app instead of android):

app:backgroundTint="@color/colorAccent"

For those using AndroidX Dependency

Along with changing dependencies, XML must also be changed.

from

<android.support.design.widget.CoordinatorLayout 

to

<androidx.coordinatorlayout.widget.CoordinatorLayout