Question

我是swift的新手，并且正在尝试使用Apple＆＃34;应用程序开发与Swift＆＃34;来自学数据持久性。我订了。我试图创建并存储一系列学生，然后我可以回忆起。问题是，当我尝试重新加载它们时，数组是空的。我真的无法理解错误，因为我没有错误，只是一个空数组。 This is what I see when I run the code. 有人可以告诉我我做错了什么吗？任何帮助表示赞赏，但可能需要为我愚蠢。欢呼声。

import Foundation

class Student: NSObject, NSCoding {

    var idNumber: String
    var forename: String
    var surname: String
    var homeAddress: String
    var postcode: String
    var homePhone: String
    var gender: String
    var tutorGroup: String
    var schoolEmail: String
    var dateOfBirth: String



    // property key strings are used for en and de coding later
    struct PropertyKey {
        static let idNumber = "idNumber"
        static let forename = "forename"
        static let surname = "surname"
        static let homeAddress = "homeAddress"
        static let postcode = "postcode"
        static let homePhone = "homePhone"
        static let gender = "gender"
        static let tutorGroup = "tutorGroup"
        static let schoolEmail = "schoolEmail"
        static let dateOfBirth = "dateOfBirth"
    }

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



    init(idNumber: String, forename: String, surname: String,
         homeAddress: String, postcode: String, homePhone: String,
         gender: String, tutorGroup: String, schoolEmail: String,
         dateOfBirth: String) {
        self.idNumber = idNumber
        self.forename = forename
        self.surname = surname
        self.homeAddress = homeAddress
        self.postcode = postcode
        self.homePhone = homePhone
        self.gender = gender
        self.tutorGroup = tutorGroup
        self.schoolEmail = schoolEmail
        self.dateOfBirth = dateOfBirth
    }


    static func loadFromFile() -> [Student]  {
        return NSKeyedUnarchiver.unarchiveObject(withFile: Student.ArchiveURL.path) as! [Student]
    }


    static func loadSampleStudents() -> [Student] {
        return [
            Student(idNumber: "13LDL", forename: "Dean", surname: "Lobo", homeAddress: "Neverland", postcode: "Far away", homePhone: "11111111", gender: "male", tutorGroup: "11L", schoolEmail: "13Lobo.d@gmail.com", dateOfBirth: "02/03/04"),

            Student(idNumber: "14LSD", forename: "Harry", surname: "Harrison", homeAddress: "21 Bushey Mill Lane", postcode: "WD23 2DD", homePhone: "01923218324", gender: "male", tutorGroup: "11L", schoolEmail: "14Harrison.h@gmail.com", dateOfBirth: "02/03/05"),

            Student(idNumber: "11LSA", forename: "Stefan", surname: "Stephens", homeAddress: "Somewhere near school", postcode: "SA12 2WP", homePhone: "01923123123", gender: "male", tutorGroup: "11L", schoolEmail: "11Adamovic.a@gmail.com", dateOfBirth: "08/03/01"),

            Student(idNumber: "11LPJ", forename: "Penny", surname: "Pennyworth", homeAddress: "12 Downing Street", postcode: "W1 12AP", homePhone: "0192311111", gender: "female", tutorGroup: "11L", schoolEmail: "11Jane.P@gmail.com", dateOfBirth: "08/03/02"),


        ]
    }

    static func saveToFile(students: [Student]) {
        NSKeyedArchiver.archiveRootObject(students, toFile: Student.ArchiveURL.path)
    }




    required convenience init?(coder aDecoder: NSCoder) {
        guard let idNumber = aDecoder.decodeObject(forKey: PropertyKey.idNumber) as? String,
            let forename = aDecoder.decodeObject(forKey: PropertyKey.forename) as? String,
            let surname = aDecoder.decodeObject(forKey: PropertyKey.surname) as? String,
            let homeAddress = aDecoder.decodeObject(forKey: PropertyKey.homeAddress) as? String,
            let postcode = aDecoder.decodeObject(forKey: PropertyKey.postcode) as? String,
            let homePhone = aDecoder.decodeObject(forKey: PropertyKey.homePhone) as? String,
            let gender = aDecoder.decodeObject(forKey: PropertyKey.gender) as? String,
            let tutorGroup = aDecoder.decodeObject(forKey: PropertyKey.tutorGroup) as? String,
            let schoolEmail = aDecoder.decodeObject(forKey: PropertyKey.schoolEmail) as? String,
            let dateOfBirth = aDecoder.decodeObject(forKey: PropertyKey.dateOfBirth) as? String
            else {
                return nil
        }

        self.init(idNumber: idNumber,
                  forename: forename,
                  surname: surname,
                  homeAddress: homeAddress,
                  postcode: postcode,
                  homePhone: homePhone,
                  gender: gender,
                  tutorGroup: tutorGroup,
                  schoolEmail: schoolEmail,
                  dateOfBirth: dateOfBirth
        )
    }


    func encode(with aCoder: NSCoder) {
        aCoder.encode(idNumber, forKey: PropertyKey.idNumber)
        aCoder.encode(forename, forKey: PropertyKey.forename)
        aCoder.encode(surname, forKey: PropertyKey.surname)
        aCoder.encode(homeAddress, forKey: PropertyKey.homeAddress)
        aCoder.encode(postcode, forKey: PropertyKey.postcode)
        aCoder.encode(homePhone, forKey: PropertyKey.homePhone)
        aCoder.encode(gender, forKey: PropertyKey.gender)
        aCoder.encode(tutorGroup, forKey: tutorGroup)
        aCoder.encode(schoolEmail, forKey: PropertyKey.schoolEmail)
        aCoder.encode(dateOfBirth, forKey: PropertyKey.dateOfBirth)
    }
}

var students: [Student] = Student.loadSampleStudents()

print(students)
Student.saveToFile(students: students)

print("Student's were saved")

var reloadedStudents: [Student] = Student.loadFromFile()

print("student's were reloaded")
print(reloadedStudents)

Answer 1

一个非常简单的错误，一个简单的修复。此行aCoder.encode(tutorGroup, forKey: tutorGroup)需要替换为：

aCoder.encode(tutorGroup, forKey: PropertyKey.tutorGroup)

所以看起来应该是这样的：

func encode(with aCoder: NSCoder) {
    aCoder.encode(idNumber, forKey: PropertyKey.idNumber)
    aCoder.encode(forename, forKey: PropertyKey.forename)
    aCoder.encode(surname, forKey: PropertyKey.surname)
    aCoder.encode(homeAddress, forKey: PropertyKey.homeAddress)
    aCoder.encode(postcode, forKey: PropertyKey.postcode)
    aCoder.encode(homePhone, forKey: PropertyKey.homePhone)
    aCoder.encode(gender, forKey: PropertyKey.gender)
    aCoder.encode(tutorGroup, forKey: PropertyKey.tutorGroup)
    aCoder.encode(schoolEmail, forKey: PropertyKey.schoolEmail)
    aCoder.encode(dateOfBirth, forKey: PropertyKey.dateOfBirth)
}

我刚刚通过设置断点（在guard else闭包内）发现了这一点。

在Swift 3中加载数据时清空数组

1 个答案: