xamarin中XAML 标记扩展

namespace MyNamespace
{   ...
    public partial class MainPage : ContentPage
    {   ...
        public const double MyBorderWidth = 3.5;
    }
}

<ContentPage ...
             xmlns:me="clr-namespace:MyNamespace;assembly=MyApp">

    <Button BorderWidth="{x:StaticExtension Member=me:MainPage.MyBorderWidth}" />
    ...
</ContentPage>