Swift3：删除包含UserDefault值的单元格时，TableView中出现错误

Question

I followed all steps provided here: The proper way to delete rows from UITableView and update array from NSUserDefaults in Swift / iOS

However, an error is caused, saying;

'Invalid update: invalid number of rows in section 0. The number of rows contained in an existing section after the update (2) must be equal to the number of rows contained in that section before the update (2), 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).'

I have created

class TableViewController: UITableViewController {

struct Section {
    var sectionName: String!
    var words: [String]!

    init(title: String, word: [String]) {
        self.sectionName = title
        self.words = word

    }
}

var arrayForRows = [String]()

var sections = [Section]()
func getData() -> [String] {
if let data = userDefaultDataSave.stringArray(forKey: "data") {
    return data
}
return []
}
override func viewDidLoad() {
    super.viewDidLoad()

    tableView.dataSource = self

    guard let data = dataDefaults.stringArray(forKey: "data") else {
        return
    }
    arrayForRows = data as [String]
    tableView.reloadData()

    sections = [
        Section(title: "A", word: []), // 1
        Section(title: "B", word: []), //2
        Section(title: "C", word: []),
        Section(title: "D", word: []),
        Section(title: "E", word: []),
        Section(title: "F", word: []),
        Section(title: "G", word: []),
        Section(title: "H", word: []),
        Section(title: "I", word: []),
        Section(title: "J", word: []),
        Section(title: "K", word: []),
        Section(title: "L", word: []),
        Section(title: "M", word: []),
        Section(title: "N", word: []),
        Section(title: "O", word: []),
        Section(title: "P", word: []),
        Section(title: "Q", word: []),
        Section(title: "R", word: []),
        Section(title: "S", word: []),
        Section(title: "T", word: []),
        Section(title: "U", word: []),
        Section(title: "V", word: []),
        Section(title: "W", word: []),
        Section(title: "X", word: []),
        Section(title: "Y", word: []),
        Section(title: "Z", word: [])
    ]


    let getAlphabetData = getData()

    for a in getAlphabetData {

        if a.hasPrefix("A") || a.hasPrefix("a") {
            if sections[0].sectionName == "A" {
                sections[0].words.append(a as String)
            }
        }

        if a.hasPrefix("B") || a.hasPrefix("b") {
            if sections[1].sectionName == "B" {
                sections[1].words.append(a as String)
            }
        }

        if a.hasPrefix("c") || a.hasPrefix("c") {
            if sections[2].sectionName == "C" {
                sections[2].words.append(a as String)
            }
        }
        if a.hasPrefix("D") || a.hasPrefix("d") {
            if sections[3].sectionName == "D" {
                sections[3].words.append(a as String)
            }
        }
        if a.hasPrefix("E") || a.hasPrefix("e") {
            if sections[4].sectionName == "E" {
                sections[4].words.append(a as String)
            }
        }
        if a.hasPrefix("F") || a.hasPrefix("f") {
            if sections[5].sectionName == "F" {
                sections[5].words.append(a as String)
            }
        }
        if a.hasPrefix("G") || a.hasPrefix("g") {
            if sections[6].sectionName == "G" {
                sections[6].words.append(a as String)
            }
        }
        if a.hasPrefix("H") || a.hasPrefix("h") {
            if sections[7].sectionName == "H" {
                sections[7].words.append(a as String)
            }
        }
        if a.hasPrefix("I") || a.hasPrefix("i") {
            if sections[8].sectionName == "I" {
                sections[8].words.append(a as String)
            }
        }
        if a.hasPrefix("J") || a.hasPrefix("j") {
            if sections[9].sectionName == "J" {
                sections[9].words.append(a as String)
            }
        }
        if a.hasPrefix("K") || a.hasPrefix("k") {
            if sections[10].sectionName == "K" {
                sections[10].words.append(a as String)
            }
        }
        if a.hasPrefix("L") || a.hasPrefix("l") {
            if sections[11].sectionName == "L" {
                sections[11].words.append(a as String)
            }
        }
        if a.hasPrefix("M") || a.hasPrefix("m") {
            if sections[12].sectionName == "M" {
                sections[12].words.append(a as String)
            }
        }
        if a.hasPrefix("N") || a.hasPrefix("n") {
            if sections[13].sectionName == "N" {
                sections[13].words.append(a as String)
            }
        }
        if a.hasPrefix("O") || a.hasPrefix("o") {
            if sections[14].sectionName == "O" {
                sections[14].words.append(a as String)
            }
        }
        if a.hasPrefix("P") || a.hasPrefix("p") {
            if sections[15].sectionName == "P" {
                sections[15].words.append(a as String)
            }
        }
        if a.hasPrefix("Q") || a.hasPrefix("q") {
            if sections[16].sectionName == "Q" {
                sections[16].words.append(a as String)
            }
        }
        if a.hasPrefix("R") || a.hasPrefix("r") {
            if sections[17].sectionName == "R" {
                sections[17].words.append(a as String)
            }
        }
        if a.hasPrefix("S") || a.hasPrefix("s") {
            if sections[18].sectionName == "S" {
                sections[18].words.append(a as String)
            }
        }
        if a.hasPrefix("T") || a.hasPrefix("t") {
            if sections[19].sectionName == "T" {
                sections[19].words.append(a as String)
            }
        }
        if a.hasPrefix("U") || a.hasPrefix("u") {
            if sections[20].sectionName == "U" {
                sections[20].words.append(a as String)
            }
        }
        if a.hasPrefix("V") || a.hasPrefix("v") {
            if sections[21].sectionName == "V" {
                sections[21].words.append(a as String)
            }
        }
        if a.hasPrefix("W") || a.hasPrefix("w") {
            if sections[22].sectionName == "W" {
                sections[22].words.append(a as String)
            }
        }
        if a.hasPrefix("X") || a.hasPrefix("x") {
            if sections[23].sectionName == "X" {
                sections[23].words.append(a as String)
            }
        }
        if a.hasPrefix("Y") || a.hasPrefix("y") {
            if sections[24].sectionName == "Y" {
                sections[24].words.append(a as String)
            }
        }
        if a.hasPrefix("Z") || a.hasPrefix("z") {
            if sections[25].sectionName == "Z" {
                sections[25].words.append(a as String)
            }
        }
    }

}

// MARK: - Table view data source

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

override func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
    return 50.0
}

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

    return arrayForRows.count
}


override func tableView(_ tableView: UITableView, titleForHeaderInSection section: Int) -> String? {
    return sections[section].sectionName
}



override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let cell = tableView.dequeueReusableCell(withIdentifier: "cell", for: indexPath)

    // Cellに値を設定する.
    cell.textLabel?.font = UIFont.systemFont(ofSize: 20)
    cell.textLabel?.textColor = UIColor.black

    cell.textLabel!.text = sections[indexPath.section].words[indexPath.row]

    return cell
}

// Override to support editing the table view.
override func tableView(_ tableView: UITableView, commit editingStyle: UITableViewCellEditingStyle, forRowAt indexPath: IndexPath) {

    if editingStyle == .delete {
        // Delete the row from the data source

        tableView.beginUpdates()

        arrayForRows.remove(at: indexPath.row)
        self.tableView.deleteRows(at: [indexPath], with: .automatic)

        let userDefaults = UserDefaults.standard
        userDefaults.set(arrayForRows, forKey: "data")
        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
    }

}

}

From another Controller, values are added into the Section's words array, by writing this way;

  class InputDataViewController: UIViewController {


 // this function is written inside UITextView in this class. 
 //But I omitted here. 

 func addData(text: String) {

    var data = self.getData()
    data.insert(text as NSString, at: 0)
    dataDefault.set(data, forKey: "data")
}


func getData() -> [String] {
    if let data = dataDefault.stringArray(forKey: "data") {
        return data
    }
    return []
 }

}

What is the problem? From the way I see it, I can understand if I did not explicitly write tableView.reloadData() or tableView.beginUpdates() and endUpdates() , but I did. What is the reason for causing this error? Could you help me?

Thanks.

Updated

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

Also, I found out that if I write this way, it worked. However, the selected one was not deleted from my table view. The first index of word was deleted from my table view regardless of the fact that I chose and deleted a row in a section. The deleted row was in another section.

  override func tableView(_ tableView: UITableView, commit editingStyle: UITableViewCellEditingStyle, forRowAt indexPath: IndexPath) {

    if editingStyle == .delete {
        // Delete the row from the data source
        //            removeHistory(index: sections[indexPath.section].words[indexPath.row])

        tableView.beginUpdates()

        let indexSet = NSMutableIndexSet()
        indexSet.add(indexPath.section)


        //let indexSet = sections[indexPath.section].words[indexPath.row] as IndexSet
        //sections.remove(at: indexPath.section)
        sections[indexPath.section].words.remove(at: indexPath.row)
        var data = getData()
        data.remove(at: indexPath.row)
        dataDefault.set(data, forKey: "data")
        dataDefault.synchronize()

        //tableView.deleteSections(indexSet, with: UITableViewRowAnimation.fade)
        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
    }
}

Answer 1

You must make sure that every time you add or delete rows, you keep your data source consistant. In your case you're removing object fron arrayForRows but your numberOfRows is using a completely different data source: sections[section].words.count

So you should either

1. Keep numberOfRows as it is and remove from sections[indexPath.section].words array
2. Change your nubmerOfRows method to return arrayForRows.count

Just make your choice what is your dataSource and pick the right option. Since you have multiple sections, you should follow the first suggestion.

Edit:

You're getting index out of bounds error because it seems you never update your sections array. You should fill all those words arrays for every section, right? But judging by the code you provided they are always empty.

Basically your implementation should look like this:

1. ViewController A displays a list of sections with words starting from a particular letter in every section
2. ViewController B creates new elements and save them to UserDefaults.
3. VC A should update sections array every time in viewWillAppear method. Just make a loop through all elements in the array from UserDefaults and put every element into the right Section object.
4. Every time a row is deleted in VC A you must remove it from a corresponding Section object, otherwise app will crash. Also you should remove the same object from UserDefaults array to keep those changes persistent.

Example for a function to insert a word into your sections array:

func insert(word: String) {
    guard word.characters.count > 0 else { return }
    let firstLetter = String(describing: word.characters.first).lowercased()
    for var section in sections {
        if section.title.lowercased().hasPrefix(firstLetter) {
            section.words.append(word)
        }
    }
}

Answer 2

Maybe the problem is that you delete row from table view before deleting data? try to delete object from your array and only then delete row from tableView

    tableView.beginUpdates()
    arrayForRows.remove(at: indexPath.row)
    self.tableView.deleteRows(at: [indexPath], with: .automatic)
    let userDefaults = UserDefaults.standard
    userDefaults.set(arrayForRows, forKey: "data")
    tableView.endUpdates()

Also try to look at your numberOfRowsInSection method. I guess it should return

arrayForRows.count