在Windows8.1中，Xamarin SearchBar不显示“X”图标来删除输入文本

<Style x:Key="CustomSearchBarStyle" TargetType="SearchBar">
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="SearchBar">
                <Grid>
                    <Grid.ColumnDefinitions>
                        <ColumnDefinition Width="*" />
                        <ColumnDefinition Width="Auto" />
                    </Grid.ColumnDefinitions>
                    <TextBox x:Name="SearchTextBox" Grid.Column="0" />
                    <Button x:Name="ClearButton" Grid.Column="1" Content="X" Click="ClearButton_Click" />
                </Grid>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

<SearchBar Style="{StaticResource CustomSearchBarStyle}" />

private void ClearButton_Click(object sender, RoutedEventArgs e)
{
    SearchTextBox.Text = string.Empty;
}