I am very new to Xamarin.Forms and had some of my projects the same issue which I couldn't solve. I can't access my in xaml defined objects in the code behind, it just says that the "name does not exist in the current context". I texted several things for solving this problem, but no way I've found in the internet worked. I can still build the app, but when I get to this special function I get an unhandled exception.
As you can see in the pictures I have some other errors too, but the function where I get the error still works.
Thanks for your help and if you need more information just ask...