/// <summary>
/// Adds a command binding to the specified <paramref name="element"/> and returns an observable sequence with two notification channels,
/// with the right channel receiving notifications when the <paramref name="command"/> is executed and the left channel
/// receiving notifications when the <paramref name="command"/> is queried as to whether it can be executed.
/// </summary>
/// <param name="command">The <see cref="ICommand"/> from which notifications are received.</param>
/// <param name="element">The <see cref="UIElement"/> that queries or executes the specified <paramref name="command"/>.</param>
/// <returns>An observable sequence with two notification channels, with the right channel receiving notifications when the <paramref name="command"/> is executed and
/// the left channel receiving notifications when the <paramref name="command"/> is queried as to whether it can be executed.</returns>
public static IObservable <Either <EventPattern <CanExecuteRoutedEventArgs>, EventPattern <ExecutedRoutedEventArgs> > > AsObservable(
this ICommand command,
UIElement element)
{
Contract.Requires(command != null);
Contract.Requires(element != null);
Contract.Ensures(Contract.Result <IObservable <Either <EventPattern <CanExecuteRoutedEventArgs>, EventPattern <ExecutedRoutedEventArgs> > > >() != null);
return(Observable2.CreateEither <EventPattern <CanExecuteRoutedEventArgs>, EventPattern <ExecutedRoutedEventArgs> >(
observer =>
{
var binding = new CommandBinding(
command,
(sender, e) => observer.OnNextRight(new EventPattern <ExecutedRoutedEventArgs>(sender, e)),
(sender, e) => observer.OnNextLeft(new EventPattern <CanExecuteRoutedEventArgs>(sender, e)));
element.CommandBindings.Add(binding);
return () => element.CommandBindings.Remove(binding);
}));
}
