How to have runtime evaluation with binding in xaml

Hi people,

I was roaming the forum and SO but I could not found an existing thread that was relevant enough to me.

Does XF has a mechanism to pass an entity that gets evaluated at runtime?

From what I could understand, having a "{Static sys:DateTime.Now}" does not do that and the date gets cached somehow. I tried to bind to a property on the VM which calls DateTime.Now but it does not work unless I do more pipework with INotifyPropertyChanged (messier). So I ended up to do that in the code behind which is far from ideal in a MVVM point of view but works:

[XamlCompilation(XamlCompilationOptions.Skip)]
public partial class MyPage : ContentPage
{
    public MyPage ()
    {
        InitializeComponent();
        Switch.Clicked += Switch_Clicked;
    }

    private void Switch_Clicked(object sender, EventArgs e)
    {
        if (BindingContext is MyViewModel vm)
        {
            vm.Switch.ExecuteCommandWith(DateTime.Now);
        }
    }
}

My need is as follow: binding entities that get evaluated at runtime when invoked. How to do that in xaml?