private void CanExecuteSpeak(object sender, CanExecuteRoutedEventArgs e)
        {
            DigitalClcok digital = (DigitalClcok)sender;

            if (digital.Time != null)
            {
                e.CanExecute = true;
            }
            else
            {
                e.CanExecute = false;
            }
        }
        private void ExecuteSpeak(object sender, ExecutedRoutedEventArgs e)
        {
            DigitalClcok digital = (DigitalClcok)sender;

            digital.SpeakTheTime(digital.Time);
        }