iOS Swift-删除tableViewCell中tableview中的行

Question

So I was trying to delete items from a tableView inside a tableViewCell. The App is pretty much a ToDo List type of app where a user can add a task and then the tasks with the same dates can be grouped together.

The dates are in their own tableView, and within the cells of those dates include a tableView of the appropriate tasks that fall under them.

However, whenever I delete a task within a tableView in a tableViewCell, the app crashes.

I have looked up the error that I receive whenever I delete a row but no changes. And they are only for normal tableViews. Not tableViews within a tableViewCell.

I have tried to add tableView.beginUpdates() and tableView.endUpdates() but problem still exists. I am not sure what to go next in this as I thought this should work and I can't really find much about deleting rows in the tableView of a tableViewCell.

The code is down below:

ToDoListTableViewController.swift (outer tableView)

class ToDoListTableViewController: UITableViewController {

    // MARK: - Properties
    var toDos = [ToDo]()
    var toDoDateGroup = [String]()
    var matchedToDoCount: Int = 0
    //var savedToDos = [ToDo]()

    override func viewDidLoad() {
        super.viewDidLoad()

        tableView.delegate = self
        tableView.dataSource = self

        // If there are saved ToDos, load them
        if let savedToDos = loadToDos() {
            toDos = savedToDos
        }
        groupToDosAccordingToDates()
        sortToDoGroupDates()
    }

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)

        //savedToDos = loadToDos()!

        groupToDosAccordingToDates()
        sortToDoGroupDates()
        reloadTableViewData()
    }

    // MARK: - Table view data source

    override func numberOfSections(in tableView: UITableView) -> Int {
        // #warning Incomplete implementation, return the number of sections
        return 1
    }

    override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        // #warning Incomplete implementation, return the number of rows
        return toDoDateGroup.count
    }

    override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {

        // Table view cells are reused and should be dequeued using a cell identifier.
        let dateCellIdentifier = "ToDoTableViewCell"
        let dateFormatter = DateFormatter()
        dateFormatter.dateFormat = "M/d/yy"
        //dateFormatter.dateFormat = "M/d/yy, h:mm a"

        guard let cell = tableView.dequeueReusableCell(withIdentifier: dateCellIdentifier, for: indexPath) as? ToDoTableViewCell else {
            fatalError("The dequeued cell is not an instance of ToDoTableViewCell.")
        }

        // Fetches the appropriate toDo for the data source layout.
        let toDoDate = toDoDateGroup[indexPath.row]

        cell.toDoDate = dateFormatter.date(from: toDoDate)!
        cell.toDoDateWeekDayLabel.text = toDoDate
        cell.toDoDateWeekDayLabel.backgroundColor = UIColor.green
        for toDo in toDos {
            //print(dateFormatter.string(from: toDo.workDate))
            //print("cell.ToDoDate Below:")
            //print(toDoDate)
            if dateFormatter.string(from: toDo.workDate) == toDoDate {
                cell.toDos.append(toDo)
            }
        }

        matchedToDoCount = cell.toDos.count
        //cell.toDoTableView.reloadData()

        return cell
    }

    override func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
        return 150
    }

    // MARK: - Actions
    @IBAction func unwindToToDoList(sender: UIStoryboardSegue) {
        if let sourceViewController = sender.source as? ToDoItemTableViewController, let toDo = sourceViewController.toDo {

            if let selectedIndexPath = tableView.indexPathForSelectedRow {
                let dateFormatter = DateFormatter()
                dateFormatter.dateFormat = "M/d/yy"
                // Update an existing ToDo
                //toDos.append(toDo)
                toDoDateGroup[selectedIndexPath.row] = dateFormatter.string(from: toDo.workDate)
                tableView.reloadRows(at: [selectedIndexPath], with: .none)
            }

            else {
                // Add a new toDo
                toDos.append(toDo)

                var newIndexPath: IndexPath
                let dateFormatter = DateFormatter()
                dateFormatter.dateFormat = "M/d/yy"

                if (toDoDateGroup.isEmpty) {
                    newIndexPath = IndexPath(row: toDoDateGroup.count, section: 0)
                    toDoDateGroup.append(dateFormatter.string(from: toDo.workDate))
                    tableView.insertRows(at: [newIndexPath], with: .automatic)
                } else {
                    groupToDosAccordingToDates()
                }
            }

            // Save the ToDos
            saveToDos()
        }
    }


    // Override to support conditional editing of the table view.
    override func tableView(_ tableView: UITableView, canEditRowAt indexPath: IndexPath) -> Bool {
        // Return false if you do not want the specified item to be editable.
        return true
    }


    // MARK: - Navigation

    // In a storyboard-based application, you will often want to do a little preparation before navigation
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        super.prepare(for: segue, sender: sender)

        switch(segue.identifier ?? "") {
        case "AddToDoItem":
            os_log("Adding a new ToDo item.", log: OSLog.default, type: .debug)
        case "ShowToDoItemDetails":
            guard let toDoItemDetailViewController = segue.destination as? ToDoItemTableViewController else {
                fatalError("Unexpected destination: \(segue.destination)")
            }

            guard let selectedToDoItemCell = sender as? ToDoGroupTableViewCell else {
                fatalError("Unexpected sender: \(sender)")
            }

            guard let indexPath = tableView.indexPath(for: selectedToDoItemCell) else {
                fatalError("The selected cell is not being displayed by the table")
            }

            let selectedToDoItem = toDos[indexPath.row]
            toDoItemDetailViewController.toDo = selectedToDoItem
        default:
            fatalError("Unexpected Segue Identifier; \(segue.identifier)")
        }
    }

    // MARK: - Private Methods
    private func saveToDos() {
        //sortToDosByWorkDate()
        let isSuccessfulSave = NSKeyedArchiver.archiveRootObject(toDos, toFile: ToDo.ArchiveURL.path)
        if isSuccessfulSave {
            os_log("ToDos successfully saved.", log: OSLog.default, type: .debug)
        } else {
            os_log("Failed to save toDos...", log: OSLog.default, type: .error)
        }
    }

    private func loadToDos() -> [ToDo]? {
        return NSKeyedUnarchiver.unarchiveObject(withFile: ToDo.ArchiveURL.path) as? [ToDo]
    }

    private func groupToDosAccordingToDates() {
        let dateFormatter = DateFormatter()
        dateFormatter.dateFormat = "M/d/yy"
        //dateFormatter.dateFormat = "M/d/yy, h:mm a"

        var newIndexPath: IndexPath

        for toDo in toDos {
            print(toDo.taskName)
            let chosenWorkDate = dateFormatter.string(from: toDo.workDate)
            if !toDoDateGroup.contains(chosenWorkDate) {
                print(chosenWorkDate)
                newIndexPath = IndexPath(row: toDoDateGroup.count, section: 0)
                toDoDateGroup.append(chosenWorkDate)
                tableView.insertRows(at: [newIndexPath], with: .automatic)
            }
        }
    }

    private func sortToDoGroupDates() {
        toDoDateGroup = toDoDateGroup.sorted(by: {
            $1 > $0
        })
    }

    private func reloadTableViewData() {
        DispatchQueue.main.async {
            self.tableView.reloadData()
        }
    }

}

ToDoTableViewCell.swift (inner tableView)

class ToDoTableViewCell: UITableViewCell, UITableViewDataSource, UITableViewDelegate {

    // MARK: - Properties

    @IBOutlet weak var toDoDateWeekDayLabel: UILabel!
    @IBOutlet weak var toDoTableView: UITableView!

    var toDos = [ToDo]()
    let dateFormatter = DateFormatter()
    var toDoDate = Date()

    let cellIdentifier = "ToDoGroupTableViewCell"

    override var intrinsicContentSize: CGSize {
        return self.intrinsicContentSize
    }

    override func awakeFromNib() {
        super.awakeFromNib()
        // Initialization code

        dateFormatter.dateFormat = "M/d/yy, h:mm a"
        sortToDosByWorkDate()
        //reloadTableViewData()
    }

    override func setSelected(_ selected: Bool, animated: Bool) {
        super.setSelected(selected, animated: animated)

        // Configure the view for the selected state
        toDoTableView.delegate = self
        toDoTableView.dataSource = self
    }

    // MARK: - Table view data source

    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        //print("Inner Cell Data");
        return toDos.count
    }

    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {

        let cellIdentifier = "ToDoGroupTableViewCell"
        let dueDateFormatter = DateFormatter()
        let workDateFormatter = DateFormatter()
        dueDateFormatter.dateFormat = "M/d/yy, h:mm a"
        workDateFormatter.dateFormat = "h:mm a"

        guard let cell = tableView.dequeueReusableCell(withIdentifier: cellIdentifier, for: indexPath) as? ToDoGroupTableViewCell  else {
            fatalError("The dequeued cell is not an instance of ToDoGroupTableViewCell.")
        }

        // Fetches the appropriate toDo for the data source layout.
        let toDo = toDos[indexPath.row]

        cell.taskNameLabel.text = toDo.taskName
        cell.workDateLabel.text = workDateFormatter.string(from: toDo.workDate)
        cell.estTimeLabel.text = toDo.estTime
        cell.dueDateLabel.text = dueDateFormatter.string(from: toDo.dueDate)

        return cell
    }

    func tableView(_ tableView: UITableView, canEditRowAt indexPath: IndexPath) -> Bool {
        // Return false if you do not want the specified item to be editable.
        return true
    }

    func tableView(_ tableView: UITableView, commit editingStyle: UITableViewCell.EditingStyle, forRowAt indexPath: IndexPath) {
        if editingStyle == .delete {
            // Delete the row from the data source of the current tableViewCell
            let toDoToBeDeleted = toDos[indexPath.row]
            tableView.beginUpdates()
            toDos.remove(at: indexPath.row)
            saveToDos(toDoToBeDeleted: toDoToBeDeleted)
            tableView.deleteRows(at: [indexPath], with: .fade)
            tableView.endUpdates()
        } else if editingStyle == .insert {
            // Create a new instance of the appropriate class, insert it into the array, and add a new row to the table view
        }
    }

    // MARK: - Private Methods

    private func saveToDos(toDoToBeDeleted: ToDo?) {
        // TODO: Refactor the deletion part of this function to be its own delete function
        // If there are existing toDos, load them
        if var savedToDos = loadToDos() {
            // If a there is a specific toDo to be deleted after save
            if toDoToBeDeleted != nil {
                print("toDoToBeDeleted is not nil")
                print(savedToDos)
                /*while let toDoIdToDelete = savedToDos.index(of: toDoToBeDeleted!) {
                    print("Index Exists in savedToDos")
                    savedToDos.remove(at: toDoIdToDelete)
                }*/
                savedToDos.removeAll{$0 == toDoToBeDeleted}
                let isSuccessfulSave = NSKeyedArchiver.archiveRootObject(savedToDos, toFile: ToDo.ArchiveURL.path)
                if isSuccessfulSave {
                    os_log("A ToDo was deleted and ToDos is successfully saved.", log: OSLog.default, type: .debug)
                }
            // If there is no specific toDo to be deleted
            } else {
                let lastToDosItem: Int = toDos.count - 1
                savedToDos.append(toDos[lastToDosItem])
                let isSuccessfulSave = NSKeyedArchiver.archiveRootObject(savedToDos, toFile: ToDo.ArchiveURL.path)
                if isSuccessfulSave {
                    os_log("A ToDo was added and ToDos is successfully saved.", log: OSLog.default, type: .debug)
                }
            }
        // If this is the initial save and no other toDos exists
        } else {
            let isSuccessfulSave = NSKeyedArchiver.archiveRootObject(toDos, toFile: ToDo.ArchiveURL.path)
            if isSuccessfulSave {
                os_log("The initial ToDo is successfully saved.", log: OSLog.default, type: .debug)
            }
        }
    }

    private func loadToDos() -> [ToDo]? {
        print("loadToDos()")
        return NSKeyedUnarchiver.unarchiveObject(withFile: ToDo.ArchiveURL.path) as? [ToDo]
    }

    private func registerCell() {
        toDoTableView.register(ToDoTableViewCell.self, forCellReuseIdentifier: "ToDoTableViewCell")
    }

    private func sortToDosByWorkDate() {
        toDos = toDos.sorted(by: {
            $1.workDate > $0.workDate
        })
     }
}

Error output when deleting a row in the tableView within a tableViewCell:

2019-08-05 00:35:03.610047-0400 Focus-N-Do[1957:40199] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Invalid update: invalid number of rows in section 0.  The number of rows contained in an existing section after the update (5) must be equal to the number of rows contained in that section before the update (3), plus or minus the number of rows inserted or deleted from that section (0 inserted, 1 deleted) and plus or minus the number of rows moved into or out of that section (0 moved in, 0 moved out).'
*** First throw call stack:
(
    0   CoreFoundation                      0x00000001095501bb __exceptionPreprocess + 331
    1   libobjc.A.dylib                     0x0000000107b66735 objc_exception_throw + 48
    2   CoreFoundation                      0x000000010954ff42 +[NSException raise:format:arguments:] + 98
    3   Foundation                          0x0000000107569877 -[NSAssertionHandler handleFailureInMethod:object:file:lineNumber:description:] + 194
    4   UIKitCore                           0x000000010c0e2e2d -[UITableView _endCellAnimationsWithContext:] + 18990
    5   UIKitCore                           0x000000010c0fc711 -[UITableView endUpdates] + 75
    6   Focus-N-Do                          0x00000001071201ac $S10Focus_N_Do02ToB13TableViewCellC05tableE0_6commit8forRowAtySo07UITableE0C_So0leF12EditingStyleV10Foundation9IndexPathVtF + 1036
    7   Focus-N-Do                          0x000000010712029b $S10Focus_N_Do02ToB13TableViewCellC05tableE0_6commit8forRowAtySo07UITableE0C_So0leF12EditingStyleV10Foundation9IndexPathVtFTo + 123
    8   UIKitCore                           0x000000010c120d90 __48-[UITableView _animateDeletionOfRowAtIndexPath:]_block_invoke + 71
    9   UIKitCore                           0x000000010c3b6235 +[UIView(Animation) performWithoutAnimation:] + 90
    10  UIKitCore                           0x000000010c120bdb -[UITableView _animateDeletionOfRowAtIndexPath:] + 219
    11  UIKitCore                           0x000000010c129739 __82-[UITableView _contextualActionForDeletingRowAtIndexPath:usingPresentationValues:]_block_invoke + 59
    12  UIKitCore                           0x000000010c07ef5e -[UIContextualAction executeHandlerWithView:completionHandler:] + 154
    13  UIKitCore                           0x000000010c084884 -[UISwipeOccurrence _performSwipeAction:inPullview:swipeInfo:] + 725
    14  UIKitCore                           0x000000010c086128 -[UISwipeOccurrence swipeActionPullView:tappedAction:] + 92
    15  UIKitCore                           0x000000010c08ad33 -[UISwipeActionPullView _tappedButton:] + 138
    16  UIKitCore                           0x000000010bedbecb -[UIApplication sendAction:to:from:forEvent:] + 83
    17  UIKitCore                           0x000000010b9170bd -[UIControl sendAction:to:forEvent:] + 67
    18  UIKitCore                           0x000000010b9173da -[UIControl _sendActionsForEvents:withEvent:] + 450
    19  UIKitCore                           0x000000010b91631e -[UIControl touchesEnded:withEvent:] + 583
    20  UIKitCore                           0x000000010bf170a4 -[UIWindow _sendTouchesForEvent:] + 2729
    21  UIKitCore                           0x000000010bf187a0 -[UIWindow sendEvent:] + 4080
    22  UIKitCore                           0x000000010bef6394 -[UIApplication sendEvent:] + 352
    23  UIKitCore                           0x000000010bfcb5a9 __dispatchPreprocessedEventFromEventQueue + 3054
    24  UIKitCore                           0x000000010bfce1cb __handleEventQueueInternal + 5948
    25  CoreFoundation                      0x00000001094b5721 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 17
    26  CoreFoundation                      0x00000001094b4f93 __CFRunLoopDoSources0 + 243
    27  CoreFoundation                      0x00000001094af63f __CFRunLoopRun + 1263
    28  CoreFoundation                      0x00000001094aee11 CFRunLoopRunSpecific + 625
    29  GraphicsServices                    0x000000011166b1dd GSEventRunModal + 62
    30  UIKitCore                           0x000000010beda81d UIApplicationMain + 140
    31  Focus-N-Do                          0x00000001071230b7 main + 71
    32  libdyld.dylib                       0x000000010a9e9575 start + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException
(lldb)

Any help would be greatly appreciated.

Answer 1

The problem is not in beginUpdates , endUpdates etc. It's in ToDoTableViewCell logics.

As the error text hints, you are deleting and/or inserting incorrect number of rows.

Consider this example: You delete 1 object from your data source (ie toDos ), you call tableView.deleteRows(at: [indexPath], with: .fade) for one indexPath .

Have that been the case, everything would be fine. But the error says that you had 3 rows before the update, now you have 5 rows after the update. And remember, you deleted 1 row, so you should be having 2 rows. How could this happen?.. App crashes.

The problem is that you are inserting objects to your data source somewhere, but are not calling tableView.inserRows(...) . You need to figure this out.

Answer 2

In your project you can use tableView datasource method canEditRowAt to delete the item from your tableView in the following manner :

override func tableView(_ tableView: UITableView, canEditRowAt indexPath: IndexPath) -> Bool {
        return true
    }
    override func tableView(_ tableView: UITableView, commit editingStyle: UITableViewCell.EditingStyle, forRowAt indexPath: IndexPath) {
        if editingStyle == .delete
        {
            toDos.remove(at: indexPath.row)
            tableView.reloadData()
        }
    }

Do remember to the reload the data in the tableView else the changes won't get reflected in tableView.

Answer 3

When deleting in commit editting method do not use begin or end updates if you want to use begin and end updates then perfrom deletion in editActionsForRowAt so do following

  func tableView(_ tableView: UITableView, commit editingStyle: UITableViewCell.EditingStyle, forRowAt indexPath: IndexPath) {
            if editingStyle == .delete {
                // Delete the row from the data source of the current tableViewCell
                let toDoToBeDeleted = toDos[indexPath.row]
                toDos.remove(at: indexPath.row)
                tableView.deleteRows(at: [indexPath], with: .fade)
                 saveToDos(toDoToBeDeleted: toDoToBeDeleted)

            } else if editingStyle == .insert {
                // Create a new instance of the appropriate class, insert it into the array, and add a new row to the table view
            }
        }

OR

     func tableView(_ tableView: UITableView, editActionsForRowAt indexPath: IndexPath) -> [UITableViewRowAction]? {

    let deleteAction = UITableViewRowAction(style: .destructive, title: "Delete") { (rowAction: UITableViewRowAction, indexPath: IndexPath) -> Void in
  let toDoToBeDeleted = toDos[indexPath.row]
                     tableView.beginUpdates()
                    toDos.remove(at: indexPath.row)
                    tableView.deleteRows(at: [indexPath], with: .fade)
                       tableView.endUpdates()
                     saveToDos(toDoToBeDeleted: toDoToBeDeleted)
    }
    return [deleteAction]
    }

And delete below part from commit editingStyle method

  let toDoToBeDeleted = toDos[indexPath.row]
        tableView.beginUpdates()
        toDos.remove(at: indexPath.row)
        saveToDos(toDoToBeDeleted: toDoToBeDeleted)
        tableView.deleteRows(at: [indexPath], with: .fade)
        tableView.endUpdates()