在 Swift 中使用 NSCoding 在分层类中进行数据持久化的最佳做法是什么？

Question

问题：我已经使用 NSKeyedArchiver 在我的 iOS 应用程序中实现了数据持久化，它目前可以保存分层数据，但只能从顶层开始 class。我怎样才能从任何级别保存整个层次结构？

背景：我正在开发一个 iOS 应用程序，它使用分层 classes 的数据结构，例如学校，教室，学生。基本上，学校 class 包含一组教室（以及其他属性，如学区、名称、phone 编号等），教室 class 包含一组学生（以及其他属性）教师、房间号等属性）和学生 class 具有每个学生的属性（例如姓名、年级、课程等）。

该应用程序有三个视图控制器，一个用于层次结构的每个级别，允许在每个级别更改数据：DistrictTableViewController 有一个 School 对象数组，可以 add/delete 个数组元素，SchoolTableViewController 有一个Classroom 对象数组，并且可以 add/delete Classroom 对象数组中的元素，而 ClassroomViewController 允许用户 add/remove/edit 学生。

我已经使用 NSCoding 在所有三个 classes 中实现了数据持久性，它目前可以在层次结构中保存数据，但我只能保存来自顶级 DistrictTableVC（应用程序入口点）的数据. DistrictTableVC 有一个 saveSchools() 方法。相反，我希望能够保存来自三个 ViewController 中任何一个的更改，例如对 Student 属性的更改将立即保存 Student 对象，以及教室中的学生数组和学校中的教室数组。

当前配置是 DistrictTableVC 将单个 School 对象传递给 SchoolTableVC，SchoolTableVC 将单个 Classroom 对象传递给 ClassroomVC。我认为我应该做的是：

创建一个名为 District 的新顶层 class，它包含学校数组并使用 NSCoding
在三个 VC 之间传递 District 对象而不是单一的较低级别对象
将 saveSchools() 方法从 DistrictTableVC 移至新 District class，允许我从三个 ViewController 中的任何一个调用它。

由于本人非专业，伸手看看：

我走在正确的轨道上吗？或
也许有人知道更好的方法？

感谢阅读！！

class DistrictTableViewController: UITableViewController {

    private let reuseIdentifier = "schoolCell"

    var schoolsArray = [School]()

    override func viewDidLoad() {
        super.viewDidLoad()

        self.navBarTitle.title = "Schools"

        // Load saved Schools if they exist, otherwise load sample data
        if let savedSchools = loadSchools() {
            schoolsArray += savedSchools
            print("Loading saved schools")

            // Update all School stats
            updateSchoolListStats()

        } else {
            // Load the sample data
            loadSampleSchools()
            print("Failed to load saved data. Loading sample data...")
        }
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

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

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

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

        let cell = tableView.dequeueReusableCell(withIdentifier: reuseIdentifier, for: indexPath) as! SchoolTableViewCell

        // Configure the cell...
        let school = schoolsArray[indexPath.row]
        school.calcSchoolStats()

        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: UITableViewCellEditingStyle, forRowAt indexPath: IndexPath) {
        if editingStyle == .delete {

            // Delete the row from the data source
            schoolsArray.remove(at: indexPath.row)
            saveSchools()

            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
        }    
    }

    // MARK: - Navigation
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {

        super.prepare(for: segue, sender: sender)

        // Deselect any selected cells
        for (_, cell) in tableView.visibleCells.enumerated() {
            cell.isSelected = false
        }

        // SchoolTableViewCell pressed: pass the selected school to SchoolsTableViewController
        if (segue.identifier ?? "") == "showSchoolDetail" {
            //guard let schoolsTableViewController = segue.destination as? SchoolsTableViewController else {
            fatalError("Unexpected destination: \(segue.destination)")
            }
            guard let selectedSchoolCell = sender as? SchoolTableViewCell else {
                fatalError("Unexpected sender: \(String(describing: sender))")
            }
            guard let indexPath = tableView.indexPath(for: selectedSchoolCell) else {
                fatalError("The selected SchoolTableViewCell is not being displayed by the table")
            }

            schoolTableViewController.school = schoolsArray[indexPath.row]
        }

        // Add button pressed: show SchoolAttributesViewController
        if addBarButtonItem == sender as? UIBarButtonItem {
            guard segue.destination is SchoolAttributesViewController else {
                fatalError("Unexpected destination: \(segue.destination)")
            }
        }
    }

    @IBAction func unwindToSessionsTableViewController(sender: UIStoryboardSegue) {

        if let sourceViewController = sender.source as? SchoolsTableViewController, let school = sourceViewController.school {

            if let selectedIndexPath = tableView.indexPathForSelectedRow {
                // Update an existing session
                schoolsArray.array[selectedIndexPath.row] = school
                tableView.reloadRows(at: [selectedIndexPath], with: .none)
            } else {
                // Add a new school to the Table View
                schoolsArray.insert(session, at: 0) // Update date source; add new school to the top of the table

                let newIndexPath = IndexPath(row: 0, section: 0)
                tableView.insertRows(at: [newIndexPath], with: .automatic)
                tableView.cellForRow(at: newIndexPath)?.isSelected = true

                tableView.cellForRow(at: newIndexPath)?.selectedBackgroundView = bgColorView
            }
            //updateSessionListStats()
            //sessionsTableView.reloadData()

            saveSchools()
        }
    }

    //MARK: Actions
    private func saveSchools() {
        let isSuccessfulSave = NSKeyedArchiver.archiveRootObject(schoolsArray, toFile: School.ArchiveURL.path)

        if isSuccessfulSave {
            os_log("Schools successfully saved", log: OSLog.default, type: .debug)
        } else {
            os_log("Failed to save schools...", log: OSLog.default, type: .error)
        }
    }
    //MARK: Private Methods
    private func updateSchoolListStats() {
        for (_, school) in schoolsArray.array.enumerated() {
            for (_, classroom) in school.classroomArray.enumerated() {
                classroom.calcStats()
            }
            school.calcSchoolStats()
        }
    }
    private func loadSchools() -> [School]? {
        return NSKeyedUnarchiver.unarchiveObject(withFile: School.ArchiveURL.path) as? [School]
    }

class School: NSObject, NSCoding {

    //MARK: Properties
    var name: String
    var district: String
    var phoneNumber: Int
    var classroomArray = [Classroom]()

    //MARK: Archiving Paths
    static let DocumentsDirectory = FileManager().urls(for: .documentDirectory, in: .userDomainMask).first!
    static let ArchiveURL = DocumentsDirectory.appendingPathComponent("schoolsArray")

    init (name: String = "Default", district: String = "", phoneNumber: Int = -1, classroomArray = [Classroom]()) {
        self.name = name
        self.district = district
        self.phoneNumber = phoneNumber
        self.classroomArray = classroomArray
    }

    func calcSchoolStats() {
    }

    //MARK: NSCoding Protocol
    func encode(with aCoder: NSCoder) {

        aCoder.encode(name, forKey: "name")
        aCoder.encode(district, forKey: "district")
        aCoder.encode(phoneNumber, forKey: "phoneNumber")
        aCoder.encode(classroomArray, forKey: "classroomArray")
    }
    required convenience init?(coder aDecoder: NSCoder) {
        // The name is required. If we cannot decode a name string, the initializer should fail.
        guard let name = aDecoder.decodeObject(forKey: "name") as? String else {
            os_log("Unable to decode the name for a School object.", log: OSLog.default, type: .debug)
            return nil
        }
        let district = aDecoder.decodeObject(forKey: "district") as! String
        let phoneNumber = aDecoder.decodeInteger(forKey: "phoneNumber")
        let classroomArray = aDecoder.decodeObject(forKey: "classroomArray") as! [Classroom]

        // Must call designated initializer.
        self.init(name: name, district: district, phoneNumber: phoneNumber, classroomArray: classroomArray)
    }
}

class Classroom: NSObject, NSCoding {

    //MARK: Properties
    var teacher: String
    var roomNumber: Int
    var studentArray = [Student]()

    //MARK: Archiving Paths
    static let DocumentsDirectory = FileManager().urls(for: .documentDirectory, in: .userDomainMask).first!
    static let ArchiveURL = DocumentsDirectory.appendingPathComponent("classroomsArray")

    init (teacher: String = "", building: Int = -1, studentArray = [Student]()) {
        self.teacher = teacher
        self.roomNumber = roomNumber
        self.studentArray = studentArray
    }

    func calcStats() {
    }

    //MARK: NSCoding Protocol
    func encode(with aCoder: NSCoder) {

        aCoder.encode(teacher, forKey: "teacher")
        aCoder.encode(roomNumber, forKey: "roomNumber")
        aCoder.encode(studentArray, forKey: "studentArray")
    }
    required convenience init?(coder aDecoder: NSCoder) {
        // The teacher is required. If we cannot decode a teacher string, the initializer should fail.
        guard let teacher = aDecoder.decodeObject(forKey: "teacher") as? String else {
            os_log("Unable to decode the teacher for a Classroom object.", log: OSLog.default, type: .debug)
            return nil
        }
        let roomNumber = aDecoder.decodeInteger(forKey: "roomNumber")
        let studentArray = aDecoder.decodeObject(forKey: "studentArray") as! [Student]

        // Must call designated initializer.
        self.init(teacher: teacher, roomNumber: roomNumber, studentArray: studentArray)
    }
}

class Student: NSObject, NSCoding {

    //MARK: Properties
    var first: String
    var last: String
    var grade: Int
    var courses: [String]

    //MARK: Archiving Paths
    static let DocumentsDirectory = FileManager().urls(for: .documentDirectory, in: .userDomainMask).first!
    static let ArchiveURL = DocumentsDirectory.appendingPathComponent("students")

    init (first: String = "", last: String = "", grade: Int = -1, courses = [String]()) {
        self.first = first
        self.last = last
        self.grade = grade
        self.courses = courses
    }

    //MARK: NSCoding Protocol
    func encode(with aCoder: NSCoder) {

        aCoder.encode(first, forKey: "first")
        aCoder.encode(last, forKey: "last")
        aCoder.encode(grade, forKey: "grade")
        aCoder.encode(courses, forKey: "courses")
    }
    required convenience init?(coder aDecoder: NSCoder) {
        // The first name is required. If we cannot decode a first name string, the initializer should fail.
        guard let first = aDecoder.decodeObject(forKey: "first") as? String else {
            os_log("Unable to decode the first name for a Student object.", log: OSLog.default, type: .debug)
            return nil
        }
        let last = aDecoder.decodeObject(forKey: "last") as! String
        let grade = aDecoder.decodeInteger(forKey: "grade")
        let courses = aDecoder.decodeObject(forKey: "courses") as! [String]

        // Must call designated initializer.
        self.init(first: first, last: last, grade: grade, courses: courses)
    }
}

Answer 1

成功了！现在每个视图控制器都有一个区域对象，并且可以在数据模型修改时调用 district.saveDistrict() 。

class 地区：NSObject, NSCoding {

//MARK: Properties
var array: [School]

//MARK: Archiving Paths
static let DocumentsDirectory = FileManager().urls(for: .documentDirectory, in: .userDomainMask).first!
static let ArchiveURL = DocumentsDirectory.appendingPathComponent("District")

init (array: [School] = [School]()) {
    self.array = array
}

//MARK: Actions
func saveDistrict() {
    let isSuccessfulSave = NSKeyedArchiver.archiveRootObject(array, toFile: District.ArchiveURL.path)

    if isSuccessfulSave {
        os_log("Schools array successfully saved", log: OSLog.default, type: .debug)
    } else {
        os_log("Failed to save schools array...", log: OSLog.default, type: .error)
    }
}
func loadSavedDistrict() -> District? {        
    var savedDistrict = District()
    if let districtConst = NSKeyedUnarchiver.unarchiveObject(withFile: District.ArchiveURL.path) as? [School] {
        savedDistrict = District(array: districtConst)
    }
    return savedDistrict
}

//MARK: NSCoding Protocol
func encode(with aCoder: NSCoder) {
    aCoder.encode(array, forKey: "array")
}
required convenience init?(coder aDecoder: NSCoder) {
    // The array is required. If we cannot decode the array, the initializer should fail.
    guard let array = aDecoder.decodeObject(forKey: "array") as? [School] else {
        os_log("Unable to decode the Schools array object.", log: OSLog.default, type: .debug)
        return nil
    }

    // Must call designated initializer.
    self.init(array: array)
}

}

在 Swift 中使用 NSCoding 在分层类中进行数据持久化的最佳做法是什么？

What is best practice for data persistence in hierarchical classes using NSCoding in Swift?

nscoding

hierarchical-data

data-persistence

ios

swift

在 Swift 中使用 NSCoding 在分层 类 中进行数据持久化的最佳做法是什么？

What is best practice for data persistence in hierarchical classes using NSCoding in Swift?

nscoding

hierarchical-data

data-persistence

ios

swift

在 Swift 中使用 NSCoding 在分层类中进行数据持久化的最佳做法是什么？