ios - NSKeyedArchiver 尝试在 Swift 中持久化数据时无法保存或加载数据

Question

我一直在使用 Apple 的开发者教程制作一个基本的 iOS 食物追踪器。当我到达“持久化数据”步骤时，我意识到使用的功能已被弃用，所以我在网上搜索找到更新/工作版本。我找到了几个有用的 NSKeyedArchiver/Unarchiver 教程，但我的代码仍然出现错误。由于存在很多问题，我一直无法找到问题的根源（是在存档数据吗？取消存档？我使用了错误的存档 URL 吗？是在完全不同的地方出现错误吗？）。

这是我第一次在 StackOverflow 上提问，我有点急需帮助。这段代码真的让我大吃一惊，我的直觉告诉我，由于我对 Swift/Xcode 的理解有限，这可能是一个简单的问题。我已经测试了很多不同版本的 NSKeyedArchiver，我想知道它是否可能是一个设置或参数。

class MealTableViewController: UITableViewController {
    
    //MARK: Properties
     
       
    var meals = [Meal]()
    

    override func viewDidLoad() {
        super.viewDidLoad()
        
        // Use the edit button item provided by the table view controller.
        navigationItem.leftBarButtonItem = editButtonItem
        
        // Load any saved meals, otherwise load sample data
        if let savedMeals = loadMeals() {
            os_log("saved meals equals load meals")
            meals += savedMeals
        }
        else {
            // Load the sample data.
            loadSampleMeals()
        }
        
    }

    // MARK: - Table view data source

    override func numberOfSections(in tableView: UITableView) -> Int {
        return 1
    }

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

    
    override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        
        // Table view cells are reused and should be dequeued using a cell identifier
        let cellIdentifier = "MealTableViewCell"

        guard let cell = tableView.dequeueReusableCell(withIdentifier: cellIdentifier, for: indexPath) as? MealTableViewCell else {
            fatalError("The dequeued cell is not an instance of MealTableViewCell")
        }
        
        // Fetches the appropriate meal for the data source layout.
        let meal = meals[indexPath.row]
        
        cell.nameLabel.text = meal.name
        cell.photoImageView.image = meal.photo
        cell.ratingControl.rating = meal.rating
        

        return cell
    }
    

    
    // 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
    }
    

    
    // Override to support editing the table view.
    override func tableView(_ tableView: UITableView, commit editingStyle: UITableViewCell.EditingStyle, forRowAt indexPath: IndexPath) {
        if editingStyle == .delete {
            // Delete the row from the data source
            meals.remove(at: indexPath.row)
            saveMeals()
            tableView.deleteRows(at: [indexPath], with: .fade)
        } 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
        }    
    }
    

    /*
    // Override to support rearranging the table view.
    override func tableView(_ tableView: UITableView, moveRowAt fromIndexPath: IndexPath, to: IndexPath) {

    }
    */

    /*
    // Override to support conditional rearranging of the table view.
    override func tableView(_ tableView: UITableView, canMoveRowAt indexPath: IndexPath) -> Bool {
        // Return false if you do not want the item to be re-orderable.
        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 "AddItem":
            os_log("Adding a new meal.", log: OSLog.default, type: .debug)
            
        case "ShowDetail":
            guard let mealDetailViewController = segue.destination as? MealViewController else{
                fatalError("Unexpected destination: \(segue.destination)")
            }
                
            guard let selectedMealCell = sender as? MealTableViewCell else{
                fatalError("Unexpected sender: \(String(describing: sender))")
                }
                
            guard let indexPath = tableView.indexPath(for: selectedMealCell) else{
                fatalError("The selected cell is not being displayed by the table")
                }
                
            let selectedMeal = meals[indexPath.row]
            mealDetailViewController.meal = selectedMeal
            
        default:
            fatalError("Unexpected Segue Identifier; \(String(describing: segue.identifier))")
        }
        
    }
    

    //MARK: Private Methods
    
    private func loadSampleMeals(){
        let burger = UIImage(named: "burger")
        let sandwich = UIImage(named: "sandwich")
        let coffee = UIImage(named: "coffee")
        let pizza = UIImage(named: "pizza")
        
        guard let meal1 = Meal(name: "Burger", photo: burger, rating: 4) else{
            fatalError("Unable to instantiate burger")
        }
        guard let meal2 = Meal(name: "Sandwich", photo: sandwich, rating: 2) else{
            fatalError("Unable to instantiate sandwich")
        }
        guard let meal3 = Meal(name: "Coffee", photo: coffee, rating: 5) else{
            fatalError("Unable to instantiate coffee")
        }
        guard let meal4 = Meal(name: "Pizza", photo: pizza, rating: 4) else{
            fatalError("Unable to instantiate pizza")
        }
        
        meals += [meal1, meal2, meal3, meal4]
    }
    
    private func saveMeals() {
        
       do {
        
        
        let mealData = try NSKeyedArchiver.archivedData(withRootObject: meals, requiringSecureCoding: true)
        
        try mealData.write(to: Meal.ArchiveURL)
        print(mealData)
        os_log("Meals successfully saved.", log: OSLog.default, type: .debug)

       } catch {
        os_log("Failed to save meals...", log: OSLog.default, type: .error)
        }
    }
            
        
    
    
    //MARK: Actions
    
    @IBAction func unwindToMealList(sender: UIStoryboardSegue) {
        
        if let sourceViewController = sender.source as? MealViewController, let meal = sourceViewController.meal {
            
            if let selectedIndexPath = tableView.indexPathForSelectedRow{
                // Update an existing meal.
                meals[selectedIndexPath.row] = meal
                tableView.reloadRows(at: [selectedIndexPath], with: .none)
            }
            else {
                // Add a new meal.
                let newIndexPath = IndexPath(row: meals.count, section: 0)
                
                meals.append(meal)
                tableView.insertRows(at: [newIndexPath], with: .automatic)
            }
            
            // Save the meals.
            saveMeals()
            
            
        }
    }
    
    private func loadMeals() -> [Meal]? {
        
        do {
            
            let fileData = try Data(contentsOf: Meal.ArchiveURL)

            let loadedStrings = try NSKeyedUnarchiver.unarchivedObject(ofClass: Meal.self, from: fileData)
            print("unarchived Strings worked")
        } catch {
           // print("Couldn't read file. \(error)")
            print("Couldn't find file.")
            print(Meal.ArchiveURL)
        }
        
        return meals
    }
    
}

我一直在单步执行代码，并注意到根本问题可能在这里：

private func saveMeals() {

 do {        
    
    let mealData = try NSKeyedArchiver.archivedData(withRootObject: meals, requiringSecureCoding: true)
    
    try mealData.write(to: Meal.ArchiveURL)
    print(mealData)
    os_log("Meals successfully saved.", log: OSLog.default, type: .debug)

   } catch {
    os_log("Failed to save meals...", log: OSLog.default, type: .error)
    }
}

当它到达“尝试 NSKeyedArchiver.archivedData(withRootObject:饭菜, requiresSecureCoding: true)”时，它立即进入“catch”，我不知道为什么。

标签： iosswiftxcodenskeyedarchivernskeyedunarchiver