Floating action button not displaying over recyclerview(which is inside a DrawerLayout)

Question

I am trying to get FAB over recyclerview which in my case will cover the whole screen. The FAB wont display even recyclerview is empty. Following is my xml code.

Answer 1

I had just created a new activity and copy pasted the whole code there and its working fine there. I still dont know the issue that what was wrong. But it worked for me this way. I had compared line by line code in two activities and they are same. Its just that floating action button is displaying in new activity and not in the old.

any ways thanks for all the help from community who tried.