private void cmbSqlServer_SelectionChanged(object sender, SelectionChangedEventArgs e)
 {
     try
     {
         var connStr = (e.AddedItems[0] as ConnectionString);
         MySqlPomocnik.CONNECTION_STRING = connStr.FullString;
         _glavniModel = new MainModel(connStr.Database);
         this.DataContext = _glavniModel;
         _glavniModel.UcitajTabele();
     }
     catch(Exception ex) { MessageBox.Show(ex.Message); }
 }