必须调用超类'日'错误的指定初始值设定项

Question

在我的应用程序中，我尝试使用数据持久性来保存数据，但出现此错误： 必须调用超类“日”错误的指定初始值设定项。

这里是我的代码：

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) 
} 

}

这里是其它类：

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 
} 

}

我要去拯救这种方式与数据仅在Day类中实现数据持久性，为什么会出现该错误？ 我是初学者，我在此基础上的苹果文档做 -

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

任何帮助将非常感激。

Answer 1

问题是由在Dayinit?(coder调用self.init引起。该调用使初始化程序convenient和子类不能满足调用指定初始化程序的要求。

的解决方案是初始化属性直接

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：你总是dayName编码为非可选字符串，所以它永远不能nil被解码的时候。 guard是无用的。

在子类中，您可能需要添加代码来解码/解码子类的属性，并调用super来考虑超类的属性。

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) 
    } 
} 

使用一个子类作为其超类属性的意义的问题则是另一回事

Answer 2

所要求Initializers-的定义：

Write the required modifier before the definition of a class initializer to indicate that every subclass of the class must implement that initializer:

You do not write the override modifier when overriding a required designated initializer:

你的情况，你做的超requiredconvenience initialiser，所以子类必须现在就实现它 - ：

代码修正 - ：

class Subject: Day { 
    var subjectName: String 
    var startsAt: String? 
    init(dayName: String,subjectName: String) { 
     self.subjectName = subjectName 
     super.init(dayName: dayName) 
    } 

    required convenience init?(coder aDecoder: NSCoder) { 
     fatalError("init(coder:) has not been implemented") 
    } 


}