swift - Must call a designated initializer of the superclass 'Day' 错误

Question

在我的应用程序中，我尝试使用数据持久化来保存数据，但出现此错误:必须调用父类(super class)“Day”错误的指定初始值设定项。

这是我的代码:

class Day: NSObject, NSCoding { // NEMA NSCODING I NSOBJECT
var dayName: String
var subjects: [Subject]?

init(dayName: String) {
    self.dayName = dayName
}

struct PropertyKey {
    static var dayName = "dayName"
    static var subjects = "subjects"
}

func encode(with aCoder: NSCoder) {
    aCoder.encode(dayName, forKey: PropertyKey.dayName)
    aCoder.encode(subjects, forKey: PropertyKey.subjects)
}

// Archiving paths
static let DocumentsDirectory = FileManager().urls(for: .documentDirectory, in: .userDomainMask).first!
static let ArchiveURL = DocumentsDirectory.appendingPathComponent("workingDays")//-namesto meals

required convenience init?(coder aDecoder: NSCoder) {
    guard let dayName = aDecoder.decodeObject(forKey: PropertyKey.dayName) as? String else {
        os_log("Unable to decode the dayName for a Day object.", log: OSLog.default, type: .debug)
        return nil
    }
    let subjects = aDecoder.decodeObject(forKey: PropertyKey.subjects) as? [Subject]
    self.init(dayName: dayName)
}

这是另一个类:

class Subject: Day {
var subjectName: String
var startsAt: String?
init(dayName: String,subjectName: String) {
    self.subjectName = subjectName
    super.init(dayName: dayName)
}
required init?(coder aDecoder: NSCoder) {
    super.init(coder: aDecoder) // here I get the error
}

我是否要通过仅在 Day 类中实现数据持久化来以这种方式保存数据，为什么会出现该错误？我是初学者，我是根据这个苹果文档做的 -

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=12&cad=rja&uact=8&ved=0ahUKEwjWoIHk4uvXAhUHaFAKHbQFCHcQFghbMAs&url=https%3A%2F%2Fdeveloper.apple.com%2Flibrary%2Fcontent%2Freferencelibrary%2FGettingStarted%2FDevelopiOSAppsSwift%2FPersistData.html&usg=AOvVaw24H5Uo4RyRY7NYIlztlgCj

如有任何帮助，我们将不胜感激。

Answer 1

问题是在 init?(coder of Day 中调用 self.init 引起的。那个调用使得初始化器 很方便 并且子类无法满足调用指定初始化程序的要求。

解决方法是直接初始化属性

required init?(coder aDecoder: NSCoder) {
    self.dayName = aDecoder.decodeObject(forKey: PropertyKey.dayName) as! String
    self.subjects = aDecoder.decodeObject(forKey: PropertyKey.subjects) as? [Subject]
}

顺便说一句:您正在将 always dayName 编码为 non-optional 字符串，因此它永远不会是 nil 解码时。 guard 没用。

在子类中，您可能需要添加代码来编码/解码子类的属性，并调用 super 来同时考虑父类(super class)的属性。

class Subject: Day {
    var subjectName: String
    var startsAt: String?

    init(dayName: String, subjectName: String) {
        self.subjectName = subjectName
        super.init(dayName: dayName)
    }

    override func encode(with aCoder: NSCoder) {
        super.encode(with: aCoder)
        aCoder.encode(subjectName, forKey: "subjectName")
        aCoder.encode(startsAt, forKey: "startsAt")
    }

    required init?(coder aDecoder: NSCoder) {
        subjectName = aDecoder.decodeObject(forKey: "subjectName") as! String
        startsAt = aDecoder.decodeObject(forKey: "startsAt") as? String
        super.init(coder: aDecoder)
    }
}

关于将子类用作其父类(super class)中的属性的意义的问题是另一回事 😉