The do statement

Question

Let's say this is our function for delete objects from the model:

func delete(indexPath: IndexPath) {

    let managedObject = self.fetchedResultsController.object(at: indexPath)
    self.managedObjectContext.delete(managedObject)

    do {

        // Save changes
        try self.managedObjectContext.save()

        // Cancel the notification
        let center = UNUserNotificationCenter.current()
        center.removeDeliveredNotifications(withIdentifiers: [managedObject.uuid!])
        center.removePendingNotificationRequests(withIdentifiers: [managedObject.uuid!])

        // Reload tableView
        self.tableView.reloadData()

    } catch {

        let alertController = UIAlertController.init(title: "Error", message: "We are sorry! Unknown error occured...", preferredStyle: .alert)
        alertController.addAction(UIAlertAction.init(title: "Close", style: .default, handler: { (action) in
            // Completion handler
        }))
        self.present(alertController, animated: true, completion: {
            // Completion block
        })
    }
}

Question:

If an error thrown, execution transfers to the catch clauses. That's nice. But what happens with the statements ( rest of the code, Cancel the notification and Reload tableView ) ? Those statements are still executable or simple ignored?

as soon as the error is thrown in this line `try self.managedObjectContext.save()`, rest of the code won't run and it will go into the catch statement. Do you still want to run the statements even if error is thrown? — Shamas S, May 04 '17 at 02:57
@ShamasS No! I do not need any statements when an error thrown. Thanks for your comment — Mannopson, May 04 '17 at 03:11
Those lines will be ignored because there was an error on the previous line. If that is what you want and that's what's happening, could you rephrase your question? — Shamas S, May 04 '17 at 03:14
@ShamasS This is an experiment. Now I know how do-catch statement works:) — Mannopson, May 04 '17 at 03:30

Shamas S · Accepted Answer · 2018-09-21T13:44:37.713

If you want your code to still be called even if an error is thrown, you can either create a separate function for it, and call it from the end of both do and catch statement. Or you can put that code in a defer statement.

Either something like

func delete(indexPath: IndexPath) {

let managedObject = self.fetchedResultsController.object(at: indexPath)
self.managedObjectContext.delete(managedObject)

do {

    // Save changes
    try self.managedObjectContext.save()
    reloadCode()

} catch {
    reloadCode()
    let alertController = UIAlertController.init(title: "Error", message: "We are sorry! Unknown error occured...", preferredStyle: .alert)
    alertController.addAction(UIAlertAction.init(title: "Close", style: .default, handler: { (action) in
        // Completion handler
    }))
    self.present(alertController, animated: true, completion: {
        // Completion block
    })
}
}

func reloadCode() {
        // Cancel the notification
        let center = UNUserNotificationCenter.current()
        center.removeDeliveredNotifications(withIdentifiers: [managedObject.uuid!])
        center.removePendingNotificationRequests(withIdentifiers: [managedObject.uuid!])

        // Reload tableView
        self.tableView.reloadData()

}

Or more neatly,

func delete(indexPath: IndexPath) {

let managedObject = self.fetchedResultsController.object(at: indexPath)
self.managedObjectContext.delete(managedObject)


  defer {
 let center = UNUserNotificationCenter.current()
        center.removeDeliveredNotifications(withIdentifiers: [managedObject.uuid!])
        center.removePendingNotificationRequests(withIdentifiers: [managedObject.uuid!])

        // Reload tableView
        self.tableView.reloadData()
}
do {

    // Save changes
    try self.managedObjectContext.save()

    // Cancel the notification


} catch {

    let alertController = UIAlertController.init(title: "Error", message: "We are sorry! Unknown error occured...", preferredStyle: .alert)
    alertController.addAction(UIAlertAction.init(title: "Close", style: .default, handler: { (action) in
        // Completion handler
    }))
    self.present(alertController, animated: true, completion: {
        // Completion block
    })
  }
}

The do statement

1 Answers1