/// <summary>
/// Handling textbox backspace input.
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void TextBox_BackKeyDown(object sender, KeyEventArgs e)
{
TextBox tb = (TextBox)sender;
if (e.Key == Key.Back && tb.Text.Length > 0 && tb.Text.Remove(tb.Text.Length - 1) == string.Empty)
{
undoStack.Push(sudoku.GetGridCopy());
mnuUndo.IsEnabled = true;
redoStack.Clear();
mnuRedo.IsEnabled = false;
}
}