Unresolved class '@string/appbar_scrolling_view_behavior'
Those who use or migrated to AndroidX, you can use the following fix to remove the error. This also works in Android Studio 3.4
app:layout_behavior="com.google.android.material.appbar.AppBarLayout$ScrollingViewBehavior"
I came across the same problem multiple times.
I always use tools:layout_behavior instead of app:layout_behavior
As Barry Staes pointed out, it looks like a bug in the IDE. However, if you're using the design library, this syntax should make the error go away:
app:layout_behavior="android.support.design.widget.AppBarLayout$ScrollingViewBehavior"