如何在Swift 2中的另一个ViewController中滑动删除Core Data TableViewCell（带行动作）

Question

To start off I just want to say I am new to iOS Programming and this is my first app so I apologize if I use incorrect terminology or what not.

My app is set up so that I can add an event using Core Data and then 2 tableViews will update with information from that Event. The first tableView I have it configured so that I can swipe to delete the cell and the information from core data.

Swipe to Delete Code:

func tableView(tableView: UITableView, commitEditingStyle editingStyle: UITableViewCellEditingStyle, forRowAtIndexPath indexPath: NSIndexPath) {

    // Enables swipe to delete for cells

    if editingStyle == .Delete {

        let appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
        let moc = appDelegate.managedObjectContext

        moc.deleteObject(events[indexPath.row])
        appDelegate.saveContext()

        events.removeAtIndex(indexPath.row)
        tableView.reloadData()
    }
}

In the other tableView however I have a UITableViewRowAction Edit button set up so that when clicked it will take the user to a EditViewController where they can edit the cell.

UITableViewRowAction Code:

func tableView(tableView: UITableView, editActionsForRowAtIndexPath indexPath: NSIndexPath) -> [UITableViewRowAction]? {

    let editAction = UITableViewRowAction(style: UITableViewRowActionStyle.Default, title: " Edit    ") { (action , indexPath ) -> Void in
        self.editing = false

        self.performSegueWithIdentifier("edit", sender: self)

        print("Edit button pressed")
    }

    return [editAction]

}

I want a button in this EditViewController to delete the cell and the Core Data information of the cell clicked like I did in the first tableView. In the EditViewController I tried using similar code to the first tableView...

var events = [Events]()

@IBAction func deleteButton(sender: AnyObject) {

    let appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
    let moc = appDelegate.managedObjectContext

    moc.deleteObject(events[indexPath.row])
    appDelegate.saveContext()

    events.removeAtIndex(indexPath.row)

    navigationController?.popViewControllerAnimated(true)

}

But this does not work because I cannot access the indexPath of the cell that I clicked on. Is there anyway that when I click the UITableViewRowAction Edit Button that I can record the indexPath of the cell and use that information in the EditViewController?

Answer 1

Step one is to pass the relevant Event to the EditViewController. First, amend your edit action closure to get the relevant Event and pass it in the performSegueWithIdentifier call:

func tableView(tableView: UITableView, editActionsForRowAtIndexPath indexPath: NSIndexPath) -> [UITableViewRowAction]? {

    let editAction = UITableViewRowAction(style: UITableViewRowActionStyle.Default, title: " Edit    ") { (action , indexPath ) -> Void in
        self.editing = false
        let eventToPass = events[indexPath.row]
        self.performSegueWithIdentifier("edit", sender: eventToPass)

        print("Edit button pressed")
    }
    return [editAction]    
}

Then implement prepareForSegue , which is called after you trigger the segue, but before the segue actually occurs. It's the place to pass information from the first view controller to the segue's destination view controller:

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    if segue.identifier == "edit" {
        let editVC = segue.destinationViewController as! EditViewController
        editVC.eventToEdit = sender as! Events
    }
}

You will need to add an eventToEdit property to your EditViewController :

var eventToEdit : Events?

You should then be able to use this property to access the various attributes of the object, and your deleteButton code can just delete this object:

@IBAction func deleteButton(sender: AnyObject) {
    let appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
    let moc = appDelegate.managedObjectContext
    moc.deleteObject(eventToEdit)
    appDelegate.saveContext()
    navigationController?.popViewControllerAnimated(true)
}

That should delete the object successfully, but your table view controller will be blissfully unaware.

Step two is to ensure that the TVC recognises that the object has been deleted. There are several ways to achieve this:

1. Add some code to viewWillAppear in the table view controller, which reloads the Events data from CoreData and reloads the table view.
2. Replace the popViewController with an Unwind Segue.
3. Implement a protocol/delegate which enables the EditViewController to directly tell the TVC that the Event has been edited or deleted.
4. Change your TVC to use a NSFetchedResultsController , which will observe inserted/updated/deleted Events and automatically update the table view.

I would begin by implementing the first of these, and then experiment with the others when you get more confident.