Q:

Xamarin. Forms AbsoluteLayout child with an absolute height and proportional width

I'm using AbsoluteLayout to render my view, essentially I have a map filled view and a button aligned to the bottom of the AbsoluteLayout
AbsoluteLayout (fill)
|--View (fill)
|--Button (bottom, full-width, 200 height)

Here is my code which uses proportional values to define the layout:
<AbsoluteLayout 
     VerticalOptions="FillAndExpand"
     HorizontalOptions="FillAndExpand">
            <maps:Map 
                AbsoluteLayout. LayoutBounds="0,0,1,1"
                AbsoluteLayout. LayoutFlags="All" /> 
             <Button
                AbsoluteLayout. LayoutBounds="0.5,1,0.5,0.15"
                AbsoluteLayout. LayoutFlags="All" />
             // ... other controls ... //
</AbsoluteLayout>

It works perfectly fine except the fact that my button has a dynamic height (proportional to the parent height).  I want to keep is static as long as I have other styles which makes it ugly whenever height is dynamic (e.g. BorderRadius). 
I tried to use absolute values for the button but now I'm constrained to have both height and width defined in absolute values while I want only the height to be defined in absolute values and width continue to take whole parent width span. 

A:

In AbsoluteLayout we can determine which four properties to be proportional or absolute(static) by setting AbsoluteLayout's LayoutFlagsAs.  So as @DavidS mentioned, you can set Button's height as static this way (say 50):
<AbsoluteLayout 
   VerticalOptions="FillAndExpand"
   HorizontalOptions="FillAndExpand">
            <maps:Map 
                AbsoluteLayout. LayoutBounds="0,0,1,1"
                AbsoluteLayout. LayoutFlags="All" /> 
             <Button
                AbsoluteLayout. LayoutBounds="0.5,1,0.5,50"
                AbsoluteLayout. LayoutFlags="PositionProportional,WidthPropor‌​tional" />
             // ... other controls ... //
</AbsoluteLayout>

