RelayCommand.cs

public class RelayCommand<T> : ICommand
{
	Action<T> exec;
	Predicate<T> canexec;

	public RelayCommand(Action<T> exec, Predicate<T> canexec = null)
	{
		Debug.Assert(exec != null);
		this.exec = exec;
		this.canexec = canexec;
	}

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

	public bool CanExecute(object parameter) => canexec?.Invoke((T)parameter) != false;

	public void Execute(object parameter) => exec((T)parameter);
}