private void MenuItemUpdate_Click(object sender, RoutedEventArgs e)
 {
     if (gViewCar.SelectedIndex != -1 && gViewCar.SelectedItems.Count == 1)
     {
         Car       car       = (Car)gViewCar.SelectedItem;
         CarDialog carDialog = new CarDialog("Update", car.MakeModel, car.EngineSize, car.Fuel);
         carDialog.Owner         = this;
         carDialog.AssignResult += (make, size, fuel) => { car.MakeModel = make; car.EngineSize = size; car.Fuel = fuel; RefreshContent(); };
         carDialog.ShowDialog();
     }
     else
     {
         MessageBox.Show("Please select One car to update!");
     }
 }
        private void AddCar_Click(object sender, RoutedEventArgs e)
        {
            CarDialog carDialog = new CarDialog("Add", "", 1.8, "");

            carDialog.AssignResult += (make, size, fuel) => { if (make != "")
                                                              {
                                                                  Car newCar = new Car(make, size, fuel); cars.Add(newCar);
                                                              }
            };
            bool?result = carDialog.ShowDialog();

            if (result == true)
            {
                RefreshContent();
            }
        }