RelayCommand.cs

using System.Windows.Input;

namespace Ventuz
{
    public class RelayCommand : ICommand
    {
        private readonly Action<object?> _execute;
        private readonly Predicate<object?>? _canExecute;

        public RelayCommand(Action<object?> execute, Predicate<object?>? canExecute = null)
        {
            _execute = execute ?? throw new ArgumentNullException(nameof(execute));
            _canExecute = canExecute;
        }

        public bool CanExecute(object? parameter) => _canExecute == null || _canExecute(parameter);

        public void Execute(object? parameter) => _execute(parameter);

        public event EventHandler? CanExecuteChanged
        {
            add => CommandManager.RequerySuggested += value;
            remove => CommandManager.RequerySuggested -= value;
        }
    }

    public static class RelayCommandExtensions
    {
        public static void CanExecuteChangedInvoke(this RelayCommand command)
        {
            var handler = typeof(RelayCommand).GetField("_canExecuteChanged", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance);
            if (handler != null)
            {
                CommandManager.InvalidateRequerySuggested();
            }
        }
    }
}