android studio: activity_main.xml does not include content_main.xml : I have two questions:
1)
I tried to add a button on the activity_main.xml, It shows. Then I thing the button is better placed in the content_main.xml. This time the button doesn't show. I make the button visibility to visible and the content_main visibility to visible as well. But the button still does not show. 

There is warning: The surrounding layout (@layout/activity_main) did not actually include this layout. Remove tools:showIn=... from the root tag.

So I guess the reason the button does not show up is that the activity_main.xml doesn't includes the content_main.xml. If it is the cause, how to solve the problem?

2)
The options menu (for settings) displays on the centre of the tool bar, not right end. How to fix it ?

Thanks