A few days ago I was looking for a way to make the Android Float action button on Xamarin Forms in a PCL project.
All I found about it, was ways to do it just for the Android project, and nothing about how to do it for iOS.
Well, after reading a lot of posts, and successives tries and multiple failures, I guess I had found a way of doing this happen, to both platforms.
Here is the Git link, of the project I submited, only with this way of resolve this problem.
Please, take a look and tell me if this really helps you.