INotifyCommandChanged patterns

[mwpowellhtx]

I wonder, is there such a pattern as INotifyCommandChanged?

The use case is implementing ICommand via RelayCommand which also provides the NotifyCanExecuteChanged method. As a means of exposing such a CommandChanged event, for example, that can be digested separating concerns into a proper WPF assembly via the dispatcher.

// Notifies clients that an ICommand instance has changed, usually which may or may not RelayCommand.CanExecute.
interface INotifyCommandChanged
{
    // Occurs when an ICommand instance changes, usually which may or may not RelayCommand.CanExecute.
    event EventHandler<NotifyCommandChangedEventArgs> CommandChanged;
}

Event handling may expose ability to invoke RelayCommand.NotifyCanExecuteChanged. Assuming invoked from the context of perhaps a property, or with ability to inform the ICommand property.

void OnCommandChanged(object sender, ICommand command, [CallerMemberName] string propertyName = "")
{
    if (command is RelayCommand relayCommand)
    {
        // TODO: sender, or this, whatever works best
        CommandChanged?.Invoke(sender, new(relayCommand, propertyName));
    }
}

And from something like WPF.

vm.CommandChanged += (sender, e) =>
{
    Application.Current.Dispatcher.Invoke(e.NotifyCanExecuteChanged);
};

With the event args connecting some pieces there.

class CommandChangedEventArgs : EventArgs
{
    public string PropertyName { get; }

    public RelayCommand RelayCommand { get; }

    public CommandChangedEventArgs(RelayCommand relayCommand, string propertyName) =>(RelayCommand, PropertyName) = (relayCommand, propertyName);

    public void NotifyCanExecuteChanged() => RelayCommand.NotifyCanExecuteChanged();
}

At least that's the 💡 idea.