C#

//IMPORT DATA FROM Mysql DataBase

        private void btnMySQL_Click(object sender, RoutedEventArgs e)
        {
             mode = 1; // i used this var to defferentiate between btnMySQL and btnSQLserver
             combdb.ItemsSource = ConnexionMysql.GetDataBasesNames();
        }

 //IMPORT DATA FROM SqlServer DataBase
        private void btnSQLserver_Click(object sender, RoutedEventArgs e)
        {
            mode = 2;
            combdb.ItemsSource = ConnexionSqlServer.GetDataBasesNames();
        }

private void combdb_SelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            switch (mode)
            {
                case 1://Connexion with Mysql database
                    {
                        datasource = combdb.SelectedItem.ToString();

                        if (ConnexionMysql.getConnexion(datasource))// Object reference not set to an instance of an object.
                        {
                           traitement......
                        }
                        else
                        {
                            MessageBox.Show("erreur");
                        }
                    }
                    break;

                case 2://Connexion with Sql Server database
                    {
                        datasource = combdb.SelectedItem.ToString();

                        if (ConnexionSqlServer.getConnexion(datasource))
                        {
                         .................
                        }
                        else
                        {
                            MessageBox.Show("erreur");
                        }
                    }
                    break;
            }
        }