viewDidLoad method

The viewDidLoad method sets the two Bar Button Item buttons to appear on the left and right side of the navigation bar respectively. The button displayed on left side is the Edit button and the one on the right side is the Add button. The Edit button will enable us to delete information of any customer and the Add button will take us to the View of the AddCustomerClass to enter information of the new customer. The title of the navigation item is set to display Customers List. After the creation and initialization of the left and right side bar button items of the navigation bar, the performFetch: message is invoked on an object returned by the fetchedResultsController method to display the result retrieved in the fetchedResultsController (that is, existing customer's list). Recall that the fetchedResultsController contains the entities specified by the fetch request, arranged on the attribute specified by the sort descriptor.