绑定FontSize不能使用Xamarin表单？

public class FontSizeBindingBehavior : Behavior<View>
{
    public static readonly BindableProperty FontSizeProperty = BindableProperty.Create(
        nameof(FontSize), typeof(double), typeof(FontSizeBindingBehavior), default(double),
        propertyChanged: OnFontSizePropertyChanged);

    public double FontSize
    {
        get => (double)GetValue(FontSizeProperty);
        set => SetValue(FontSizeProperty, value);
    }

    protected override void OnAttachedTo(View bindable)
    {
        base.OnAttachedTo(bindable);
        bindable.BindingContextChanged += OnBindingContextChanged;
        SetFontSize(bindable);
    }

    protected override void OnDetachingFrom(View bindable)
    {
        bindable.BindingContextChanged -= OnBindingContextChanged;
        base.OnDetachingFrom(bindable);
    }

    private void OnBindingContextChanged(object sender, EventArgs e)
    {
        if (sender is View view)
        {
            SetFontSize(view);
        }
    }

    private static void OnFontSizePropertyChanged(BindableObject bindable, object oldValue, object newValue)
    {
        if (bindable is View view && newValue is double fontSize)
        {
            view.SetValue(View.FontSizeProperty, fontSize);
        }
    }

    private void SetFontSize(View view)
    {
        view.SetValue(View.FontSizeProperty, FontSize);
    }
}

<Label Text="Hello, Xamarin.Forms!">
    <Label.Behaviors>
        <local:FontSizeBindingBehavior FontSize="{Binding YourFontSize}" />
    </Label.Behaviors>
</Label>