private void BT_Validate_Click(object sender, RoutedEventArgs e)
        {
            string name  = this.TB_Name.Text;
            double coeff = this.NUD_Coeff.Value;
            Color  color = this.colorDialog.Color;

            if (!string.IsNullOrEmpty(name))
            {
                Subject subject = new Subject(name, (float)coeff, color);
                SettingsManager.AddSubject(subject);

                this.DialogResult = true;
            }
            else
            {
                System.Windows.MessageBox.Show("Saisissez le nom de la matière !",
                                               "Agenda - Virtuel",
                                               MessageBoxButton.OK,
                                               MessageBoxImage.Information);
                this.TB_Name.Focus();
            }
        }