Picker hidden behind listview, On Pad and Iphone

        <StackLayout Orientation="Horizontal">
        <Label  Text="Select Facility"  Style="{StaticResource BlueLabel}"/>
         <Picker x:Name="FacilityPicker" Style="{StaticResource BlueLabel} "
                ItemsSource="{Binding Facilities}"
                ItemDisplayBinding="{Binding value}"
                SelectedItem="{Binding SelectedFacility}"/>
        <Label  x:Name="FacilitySelected" Text="{Binding ChangeFacility}"  Style="{StaticResource BlueLabel}"/>            
    </StackLayout>        

    <!--Header Content-->        
    <Grid x:Name="HeaderGrid" RowSpacing="3" ColumnSpacing="1">
        <Grid.RowDefinitions>
            <RowDefinition Height="*" />
            <RowDefinition Height="10"/>
            <RowDefinition Height="auto" />
            <RowDefinition Height="auto" />
        </Grid.RowDefinitions>
  </Grid>    
    <!--End of Header Content-->

    <!--Data Content-->
    <Local:CustomListView ItemsSource="{Binding EnvItemsList}"
                  HasUnevenRows="True"                      
                  ItemClickCommand="{Binding ItemClickCommand}">
        <Local:CustomListView.ItemTemplate>
            <DataTemplate>
                <ViewCell>
                    <StackLayout Orientation="Horizontal">
                        <Grid BackgroundColor="Purple" 
                              Padding="10" RowSpacing="20" Margin="10">
                            <Grid.RowDefinitions>
                                <RowDefinition Height="80"/>
                            </Grid.RowDefinitions>
                            <Grid.ColumnDefinitions>
                                <ColumnDefinition Width="80"/>
                            </Grid.ColumnDefinitions>
                            <Label Text="{Binding EnvAudititemID}"
                                   FontSize="50"
                                   TextColor="White" Grid.Row="0" Grid.Column="0"
                                   HorizontalOptions="Center"
                                   VerticalOptions="Center"/>
                        </Grid>
                        <StackLayout Orientation="Vertical">
                            <Label Text="{Binding ItemA}"
                                   FontSize="24"
                                   TextColor="Black"/>
                            <Label Text="{Binding ItemB}"                            
                                   FontSize="20"
                                   TextColor="Gray"/>
                        </StackLayout>
                    </StackLayout>
                </ViewCell>
            </DataTemplate>
        </Local:CustomListView.ItemTemplate>
    </Local:CustomListView>
</StackLayout>