How to show ActivityIndicator that covers whole screen including Navigation bar - Xamarin Forms

My code for ActivityIndicator is below:

    <ActivityIndicator x:Name="actWebRequest"
                    Color="White"
                    IsVisible="{Binding IsLoading}"
                    IsRunning="{Binding IsLoading}"
                    AbsoluteLayout.LayoutBounds="0, 0, 1, 1"
                    AbsoluteLayout.LayoutFlags= "All" 
                    BackgroundColor="#70383838"/>

I know, I can put it inside absolute layout or any other layour.

MY NEED:
I would like to show it for the whole screen which should also overlay above Navigation bar's back button, title and slide menu icon on my top right side in Navigation bar.
I MEAN FOR THE WHOLE SCREEN.

How can I achieve this using Xaml in Xamarin Forms.

Thank you a lot in advance for the help.