Floating Action Button does not responds when it clicked/touched

Question

I am using a floating action button(FAB) in my application to show Dialogs, everything is worked just fine when I tested my app in Xperia Z with Lopllipop 5.1.1.
However

Answer 1

The problem in here is that I declared the FAB before the declaration of listView. Somehow by relocating the declaration of FAB after the the declaration of listView it will solved the problem.
From:

To:

Just as simple as that.