Replacement for Xamarin.Forms.OnPlatform which supports the Windows (WinRT) platforms.

OnPlatform2.cs

namespace InTheHand.Forms
{
    /// <summary>
    /// Replacement for Xamarin.Forms.OnPlatform which supports the Windows (WinRT) platforms.
    /// </summary>
    /// <typeparam name="T"></typeparam>
    public sealed class OnPlatform2<T>
    {
        public OnPlatform2()
        {
            Android = default(T);
            iOS = default(T);
            WinPhone = default(T);
            Windows = default(T);
            Other = default(T);
        }

        public T Android{ get; set;}

        public T iOS { get; set; }

        public T WinPhone { get; set; }

        /// <summary>
        /// The value to use for WinRT (Windows Phone 8.1 and Windows 8.1).
        /// </summary>
        public T Windows { get; set; }

        /// <summary>
        /// Currently unused.
        /// </summary>
        public T Other { get; set; }

        public static implicit operator T(InTheHand.Forms.OnPlatform2<T> onPlatform)
        {
            switch(Xamarin.Forms.Device.OS)
            {
                case Xamarin.Forms.TargetPlatform.Android:
                    return onPlatform.Android;

                case Xamarin.Forms.TargetPlatform.iOS:
                    return onPlatform.iOS;

                case Xamarin.Forms.TargetPlatform.WinPhone:
                    return onPlatform.WinPhone;

                case Xamarin.Forms.TargetPlatform.Windows:
                    return onPlatform.Windows;

                default:
                    return onPlatform.Other;
            }
        }   
    }
}

To use OnPlatform2 from XAML add an XML namespace directive e.g.
xmlns:forms="clr-namespace:InTheHand.Forms;assembly=YOURASSEMBLY"

Then use in your XAML wherever you want to provide platform specific values e.g.

<Grid.Padding> <forms:OnPlatform2 x:TypeArguments="Thickness" iOS="5" Android="5" Windows="0,10,0,5"/> </Grid.Padding>