RelayCommand.cs

using System;
using System.Windows.Input;

namespace Jon.Wpf.CustomControls
{
    public class RelayCommand : ICommand
    {
        public RelayCommand(Action<object> execute, Predicate<object> canExecute = null)
        {
            _execute = execute;
            _canExecute = canExecute;
        }
        private readonly Action<object> _execute;
        private readonly Predicate<object> _canExecute;
        public event EventHandler CanExecuteChanged
        {
            add { CommandManager.RequerySuggested += value; }
            remove { CommandManager.RequerySuggested -= value; }
        }
        public bool CanExecute(object parameter)
        {
            return _canExecute == null || _canExecute(parameter);
        }

        public void Execute(object parameter)
        {
            _execute(parameter);
        }
    }

    public class RelayCommand<T> : ICommand
    {
        public RelayCommand(Action<T> execute, Func<T, bool> canExecute = null)
        {
            this.execute = execute ?? throw new ArgumentNullException(nameof(execute));
            this.canExecute = canExecute;
        }
        private readonly Action<T> execute;
        private readonly Func<T, bool> canExecute;

        public event EventHandler CanExecuteChanged
        {
            add { CommandManager.RequerySuggested += value; }
            remove { CommandManager.RequerySuggested -= value; }
        }
        public bool CanExecute(object parameter)
        {
            if (parameter is T typedParameter && (canExecute == null || canExecute(typedParameter)))
            {
                return true;
            }

            return false;
        }

        public void Execute(object parameter)
        {
            if (parameter is T typedParameter)
            {
                execute(typedParameter);
            }
        }
    }

}