protected virtual void OnBeforeUndo(BeforeUndoEventArgs e)
{
if(BeforeUndo != null)
BeforeUndo(this, e);
}
public void Undo()
{
if(!CanUndo)
throw new CommandHistoryEmptyException("Nothing to undo.");
IUndoableCommand command = commandHistory.Peek();
BeforeUndoEventArgs args = new BeforeUndoEventArgs() { Cancel = false, Command = command };
OnBeforeUndo(args);
if(!args.Cancel)
{
command.Undo();
undoneCommands.Push(commandHistory.Pop());
OnCommandHistoryChanged();
}
}