ChangeSublayerRenderer.xaml

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:esriUI="clr-namespace:Esri.ArcGISRuntime.Xamarin.Forms;assembly=Esri.ArcGISRuntime.Xamarin.Forms"
             x:Class="ArcGISRuntime.Samples.ChangeSublayerRenderer.ChangeSublayerRenderer">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto" />
            <RowDefinition Height="*" />
        </Grid.RowDefinitions>

        <Label x:Name="ChangeSublayerRendererInstructionsLabel"
               Grid.Row="0"
               FontSize="Small"
               Text="Click the 'Change Sublayer Renderer' button to apply a unique value renderer to the counties sub-layer.">
        </Label>
        <Button x:Name="ChangeSublayerRendererButton"
                Grid.Row="1"
                Text="Change sublayer renderer"
                Clicked="ChangeSublayerRendererButton_Clicked"/>
        <esriUI:MapView x:Name="MyMapView" 
                        Grid.Row="2"/>
    </Grid>
</ContentPage>