有没有办法在app.xaml文件的样式中指定一个OnPlatform？

<Application.Resources>
    <ResourceDictionary>
        <Style x:Key="MyLabelStyle" TargetType="Label">
            <Setter Property="FontSize">
                <Setter.Value>
                    <OnPlatform x:TypeArguments="x:Double">
                        <On Platform="iOS">20</On>
                        <On Platform="Android">18</On>
                        <On Platform="UWP">22</On>
                    </OnPlatform>
                </Setter.Value>
            </Setter>
        </Style>
    </ResourceDictionary>
</Application.Resources>