arrays - 尝试保存到 NSUserdefaults 时出错

Question

我有一个按以下方式工作的表。如果选择了一行，则将与所选行对应的金额添加到 var total，并添加一个复选标记。如果取消选择，金额将被减去，复选标记将设置为无。 在尝试将数据保存到 NSUserDefaults 或从中检索数据之前，我的代码工作正常。 错误是:当我选择第一行时，它减去而不是添加金额；选择一行后，如果我点击后退按钮然后返回同一屏幕，则不会显示复选标记。 在此构造中，当我尝试从 NSUserDefaults 检索 indexPathForCellSelected 时计算结果为 nil，即使我在进行分配之前检查了 if indexPathForCellSelected != nil。 fatal error :在展开可选值时意外发现 nil

if indexPathForCellSelected != nil { self.tableView.cellForRowAtIndexPath(indexPathForCellSelected!)?.
accessoryType = .Checkmark
}



class NinethViewController: UIViewController, UITableViewDelegate,UITableViewDataSource {

var total = 0
var indexRowRetrieved:Int?
var rowSelected:Int?
var indexRowSelectedKey = "indexRowKey"
var amountKey = "amountKey"
var totalKey = "totalKey"
let indexPathKey = "indexPathForCellSelected"
var indexPathForCellSelected: NSIndexPath?


struct Item {
    var name:String // name of the row
    var selected:Bool // whether is selected or not
    var amount: Int // value of the item
}

var extras = [

    Item(name:"Inside Cabinets",selected: false, amount: 5),
    Item(name:"Inside Fridge",selected: false, amount: 5),
    Item(name:"Inside Oven",selected: false, amount: 5),
    Item(name:"Laundry wash & dry",selected: false, amount: 10),
    Item(name:"Interior Windows", selected: false, amount: 5)
]


@IBOutlet weak var tableView: UITableView!

override func viewDidLoad() {
    super.viewDidLoad()
}

override func viewDidAppear(animated: Bool) {
    super.viewDidAppear(animated)

    // loadData from NSUserDefaults
    loadData()
}

func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    return extras.count
}

func numberOfSectionsInTableView(tableView: UITableView) -> Int {
    return 1
}

// configure the cell
func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath)
    -> UITableViewCell     {
        let cell = tableView.dequeueReusableCellWithIdentifier("Cell")
        cell?.textLabel?.text = extras[indexPath.row].name
        return cell!
}

func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {

    // if the cell has not been selected before
    if !extras[indexPath.row].selected  {

        // marks the cell as selected
        extras[indexPath.row].selected = true
        tableView.cellForRowAtIndexPath(indexPath)?.accessoryType = .Checkmark

        self.total += extras[indexPath.row].amount
        indexPathForCellSelected = indexPath
        rowSelected = indexPath.row
        print(total)

        //   save all info in NSUserDefaults
                saveData()

    } else {
        // marks the cell as not selected
        extras[indexPath.row].selected = false
        tableView.cellForRowAtIndexPath(indexPath)?.accessoryType = .None

        self.total -= extras[indexPath.row].amount
        print(total)



    }
}


func saveData(){

    // save indexPathForCellSelected in NSUserDefaults
    if indexPathForCellSelected != nil {
         let data = NSKeyedArchiver.archivedDataWithRootObject(indexPathForCellSelected!)
                     NSUserDefaults.standardUserDefaults().setObject(data, forKey: indexPathKey)

        // save indexRowSelected
        NSUserDefaults.standardUserDefaults().setInteger(rowSelected!, forKey: indexRowSelectedKey)

        // save amount for corresponding row in NSUserDefaults
        NSUserDefaults.standardUserDefaults().setObject(extras[rowSelected!].amount, forKey: amountKey)

        //save total in NSUserDefaults
        NSUserDefaults.standardUserDefaults().setObject(total, forKey: totalKey)

    }

}



func loadData() {
    //retrieve indexPathForCellSelected from NSUserDefaults
    if let retrievedIndexPath = NSUserDefaults.standardUserDefaults().dataForKey(indexPathKey) {
        if let data1 = NSKeyedUnarchiver.unarchiveObjectWithData(retrievedIndexPath) as? NSIndexPath{
            indexPathForCellSelected = data1
        }
    }


    // retrieve the index for row selected to select the state of the row: true or false
    if let retrievedIndexRow = NSUserDefaults.standardUserDefaults().integerForKey(indexRowSelectedKey) as? Int      {
            indexRowRetrieved = retrievedIndexRow
                extras[retrievedIndexRow].selected = true
    }

    // retrieve amount for corresponding row in NSUserDefaults
    if let itemAmount =  NSUserDefaults.standardUserDefaults().objectForKey(amountKey) as? Int {
        extras[indexRowRetrieved!].amount = itemAmount

        // assign checkmark to row selected
            if indexPathForCellSelected != nil {
                self.tableView.cellForRowAtIndexPath(indexPathForCellSelected!)?.accessoryType = .Checkmark
        }
    }
    // retrieve total from NSUserDefaults
        if let totalRetrieved = NSUserDefaults.standardUserDefaults().objectForKey(totalKey) as? Int {
            total = totalRetrieved
                print(total)
      }
   }
}

Answer 1

我不知道你为什么要为之前选择的单元格保存所有 NSIndexPath，而根据你之前的问题和这个问题，你只需要保存所选单元格的索引和当您转到另一个 Controller 时，您拥有的总值(value)。您可以通过以下方式进行:

var frequency = [
    Item(name:"Every week",selected: false, amount: 30),
    Item(name:"Every 2 weeks",selected: false, amount: 30),
    Item(name:"Every 4 weeks",selected: false, amount: 30),
    Item(name:"Once",selected: false, amount: 40),
    Item(name:"End of tenancy cleaning", selected: false, amount: 44)
]

var indexPathForCellSelected: NSIndexPath?
var total = 0

let indexPathKey = "indexPathForCellSelectedNinethViewControllerKey"
let totalKey = "totalNinethViewControllerKey"

override func viewDidLoad() {
    super.viewDidLoad()

    loadData()
}

func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {

    let cell = tableView.dequeueReusableCellWithIdentifier("Cell", forIndexPath: indexPath)
    cell.textLabel?.text = frequency[indexPath.row].name
    if let _ = indexPathForCellSelected where indexPath == indexPathForCellSelected {
        cell.accessoryType = .Checkmark
    }
    return cell
}

func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {

    if !frequency[indexPath.row].selected {

        // this avoid set initial value for the first time
        if let index = indexPathForCellSelected {
            // clear the previous cell
            frequency[index.row].selected = false
            tableView.cellForRowAtIndexPath(index)?.accessoryType = .None
            self.total -= frequency[index.row].amount
        }

        // mark the new one
        frequency[indexPath.row].selected = true
        tableView.cellForRowAtIndexPath(indexPath)?.accessoryType = .Checkmark

        indexPathForCellSelected = indexPath
        self.total += frequency[indexPath.row].amount

        saveData()
    }
}

private func saveData() {

    // save the index for the cell selected in NSUserDefaults
    NSUserDefaults.standardUserDefaults().setInteger(indexPathForCellSelected!.row, forKey: indexPathKey)

    // save total in NSUserDefaults
    NSUserDefaults.standardUserDefaults().setInteger(total, forKey: totalKey)
}

private func loadData() {

    // get the values from NSUserDefaults if exist
    if let indexValue = NSUserDefaults.standardUserDefaults().valueForKey(indexPathKey), totalValue = NSUserDefaults.standardUserDefaults().valueForKey(totalKey) {
        indexPathForCellSelected = NSIndexPath(forRow: indexValue as! Int, inSection: 0)
        total = totalValue as! Int
    }
}

希望对你有帮助