How to always ScrollBar in ScrollView

Hi, i have a ScrollView with a Grid Laout with some elements like this in xaml:

    <?xml version="1.0" encoding="utf-8" ?>
    <ContentView xmlns="http://xamarin.com/schemas/2014/forms" xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"                       x:Class="Cardioline.controls.cntButton">
        <ContentView.Content>
        <ScrollView x:Name="_myScrollView" Orientation = "Vertical" VerticalOptions="FillAndExpand" >
              <Grid x:Name="_myGrid" RowSpacing="0" ColumnSpacing="0" Padding="0">
                ...some rows and some elements
              </Grid>
        </ScrollView>
        </ContentView.Content>
    </ContentView>

I have make a custom ScrollViewRender but how show always the ScrollBar ?