Encode/Decoding 在 Swift 3 中与 NSCoder 约会？

Question

我正在编写一个基于 Apple 的 FoodTracker 教程的规划器应用程序，它存储几个字符串、一个日期和每个分配的 UIImage。我在 encoding/decoding 日期遇到了问题。我不确定是哪一个，因为控制台输出会随着每次细微的修改而改变，但据我所知，我的代码将日期保存为 nil，然后当它尝试加载该日期时，它意外地发现 nil 和崩溃。因为我对Swift比较陌生，而且Swift3是个头疼半天的问题，我也不太清楚问题到底出在哪里。这是我认为应该工作的代码：

class Assignment: NSObject, NSCoding {

//MARK: Properties

var name: String
var className: String
var assignmentDescription: String
var materials: String
var dueDate: Date?
var assignmentImage: UIImage?

//MARK: Archiving Paths

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

//MARK: Types

struct PropertyKey {
    static let nameKey = "name"
    static let classNameKey = "className"
    static let assignmentDescriptionKey = "assignmentDescription"
    static let materialsKey = "materials"
    static let dueDateKey = "dueDate"
    static let assignmentImageKey = "assignmentImage"
}

//MARK: Initialization

init?(name: String, className: String, assignmentDescription: String, materials: String, dueDate: Date, assignmentImage: UIImage?) {
    //Initialize stored properties.
    self.name = name
    self.className = className
    self.assignmentDescription = assignmentDescription
    self.materials = materials
    self.dueDate = dueDate
    self.assignmentImage = assignmentImage

    super.init()

    //Initialization should fail if there is no name and no class.
    if name.isEmpty && className.isEmpty {
        print("Failed to initialize an assignment.")
        return nil
    }
}

//MARK: NSCoding

func encode(with aCoder: NSCoder) {
    aCoder.encode(name, forKey: PropertyKey.nameKey)
    aCoder.encode(className, forKey: PropertyKey.classNameKey)
    aCoder.encode(assignmentDescription, forKey: PropertyKey.assignmentDescriptionKey)
    aCoder.encode(materials, forKey: PropertyKey.materialsKey)
    aCoder.encode(dueDate, forKey: PropertyKey.dueDateKey)
    aCoder.encode(assignmentImage, forKey: PropertyKey.dueDateKey)
}

required convenience init?(coder aDecoder: NSCoder) {
    //Required fields.
    let name = aDecoder.decodeObject(forKey: PropertyKey.nameKey) as! String
    let className = aDecoder.decodeObject(forKey: PropertyKey.classNameKey) as! String

    //Optional fields.
    let assignmentDescription = aDecoder.decodeObject(forKey: PropertyKey.assignmentDescriptionKey) as? String
    let materials = aDecoder.decodeObject(forKey: PropertyKey.materialsKey) as? String
    let dueDate = aDecoder.decodeObject(forKey: PropertyKey.dueDateKey) as! Date
    let assignmentImage = aDecoder.decodeObject(forKey: PropertyKey.assignmentImageKey) as? UIImage

    //Must call designated initializer.
    self.init(name: name, className: className, assignmentDescription: assignmentDescription!, materials: materials!, dueDate: dueDate, assignmentImage: assignmentImage)
}

如有任何见解，我们将不胜感激。

编辑：

在 Duncan C 的帮助和 Xcode 的修复下，这就是 required convenience init?(coder aDecoder: NSCoder) 现在的样子：

//Required fields.
    let newName = aDecoder.decodeObject(forKey: PropertyKey.nameKey) as! String
    let newClassName = aDecoder.decodeObject(forKey: PropertyKey.classNameKey) as! String

    //Optional fields.
    var newAssignmentImage: UIImage?
    var newDueDate: Date

    let newAssignmentDescription = aDecoder.decodeObject(forKey: PropertyKey.assignmentDescriptionKey) as! String
    let newMaterials = aDecoder.decodeObject(forKey: PropertyKey.materialsKey) as! String

    if aDecoder.containsValue(forKey: PropertyKey.dueDateKey) {
        newDueDate = aDecoder.decodeObject(forKey: PropertyKey.dueDateKey) as! Date
    } else {
        newDueDate = Date()
        if aDecoder.containsValue(forKey: PropertyKey.assignmentImageKey) {
            newAssignmentImage = aDecoder.decodeObject(forKey: PropertyKey.assignmentImageKey) as? UIImage
        } else {
            newAssignmentImage = UIImage(named: "sampleAssignmentImage")
        }
    }

    //Must call designated initializer.
    self.init(name: newName, className: newClassName, assignmentDescription: newAssignmentDescription, materials: newMaterials, dueDate: newDueDate, assignmentImage: newAssignmentImage)!

它编译了，但它仍然在 newDueDate = aDecoder.decodeObject(forKey: PropertyKey.dueDateKey) as! Date

行抛出 fatal error: unexpectedly found nil while unwrapping an Optional value

编辑 2：

回到我的原始代码并将 ? 更改为 ! 后，这就是我的代码的样子：

 //Required fields.
    let name = aDecoder.decodeObject(forKey: PropertyKey.nameKey) as! String
    let className = aDecoder.decodeObject(forKey: PropertyKey.classNameKey) as! String

    //Optional fields.
    let assignmentDescription = aDecoder.decodeObject(forKey: PropertyKey.assignmentDescriptionKey) as! String
    let materials = aDecoder.decodeObject(forKey: PropertyKey.materialsKey) as! String
    let dueDate = aDecoder.decodeObject(forKey: PropertyKey.dueDateKey) as! Date
    let assignmentImage = aDecoder.decodeObject(forKey: PropertyKey.assignmentImageKey) as! UIImage

    //Must call designated initializer.
    self.init(name: name, className: className, assignmentDescription: assignmentDescription, materials: materials, dueDate: dueDate, assignmentImage: assignmentImage)

它编译了，但它仍然在 let dueDate = aDecoder.decodeObject(forKey: PropertyKey.dueDateKey) as! Date

行抛出 fatal error: unexpectedly found nil while unwrapping an Optional value

编辑 3（工作）：

对于任何感兴趣的人，这里是修改后的原始代码部分：

属性：

//You can't encode optional values, so you don't use `?` here.
var dueDate: Date
var assignmentImage: UIImage

初始化程序：

//Removed the `?` after UIImage because it isn't an Optional.
init?(name: String, className: String, assignmentDescription: String, materials: String, dueDate: Date, assignmentImage: UIImage)

解码器（required convenience init?(coder aDecoder: NSCoder)）：

//Required fields.
let name = aDecoder.decodeObject(forKey: PropertyKey.nameKey) as! String
let className = aDecoder.decodeObject(forKey: PropertyKey.classNameKey) as! String

//Optional fields.
let assignmentDescription = aDecoder.decodeObject(forKey: PropertyKey.assignmentDescriptionKey) as! String //This String should use `!` instead of `?`.
let materials = aDecoder.decodeObject(forKey: PropertyKey.materialsKey) as! String //This String should use `!` instead of `?`.
let dueDate = aDecoder.decodeObject(forKey: PropertyKey.dueDateKey) as! Date
//Check for the UIImage being nil. If it is, assign some default image to it so that it doesn't unwrap nil and crash.
var assignmentImage: UIImage!
if aDecoder.decodeObject(forKey: PropertyKey.assignmentImageKey) == nil {
    assignmentImage = UIImage(named: "SampleAssignmentImage")
}
else {
    assignmentImage = aDecoder.decodeObject(forKey: PropertyKey.assignmentImageKey) as! UIImage
}

//Must call designated initializer.
//`materials` and `assignmentDescription` don't need `!` now because they're already unwrapped.
self.init(name: name, className: className, assignmentDescription: assignmentDescription, materials: materials, dueDate: dueDate, assignmentImage: assignmentImage)

它并不完美，但它确实有效。

Answer 1

您只能对 Objective-C 对象进行编码，而可选 Date? 不是 Objective-C 对象。试着说：

aCoder.encode(dueDate! as NSDate, forKey: PropertyKey.dueDateKey)

Answer 2

正如 Matt 所说，您不能对可选项进行编码。不过，与其强行解包，我建议添加一个 if let 并且仅在可选值包含以下值时才将其添加到存档中：

func encode(with aCoder: NSCoder) {
        aCoder.encode(name, forKey: PropertyKey.nameKey)
        aCoder.encode(className, forKey: PropertyKey.classNameKey)
        aCoder.encode(assignmentDescription, forKey: PropertyKey.assignmentDescriptionKey)
        aCoder.encode(materials, forKey: PropertyKey.materialsKey)
        if let date = dueDate {
            aCoder.encode(date, forKey: PropertyKey.dueDateKey)

        }
        if let image = assignmentImage {
            aCoder.encode(image, forKey: PropertyKey.dueDateKey)
        }
    }

然后在你的 init(coder:) 方法中，在解码之前检查密钥是否存在：

required convenience init?(coder aDecoder: NSCoder) {
    //Required fields.
    name = aDecoder.decodeObject(forKey: PropertyKey.nameKey) as! String
    className = aDecoder.decodeObject(forKey: PropertyKey.classNameKey) as! String

    //Optional fields.
    assignmentDescription = aDecoder.containsValue(forKey: PropertyKey.assignmentDescriptionKey) as? String
    materials = aDecoder.decodeObject(forKey: PropertyKey.materialsKey) as? String

    if aDecoder.containsValue(forKey: PropertyKey.dueDateKey) {
        dueDate = aDecoder.decodeObject(forKey: PropertyKey.dueDateKey) as! Date
    } else {
       dueDate = nil
    if aDecoder.containsValue(forKey: PropertyKey.assignmentImageKey) {
        assignmentImage = aDecoder.decodeObject(forKey: PropertyKey.assignmentImageKey) as? UIImage
    } else {
      assignmentImage = nil
    }

    //Must call designated initializer.
    self.init(name: name, className: className, assignmentDescription: assignmentDescription!, materials: materials!, dueDate: dueDate, assignmentImage: assignmentImage)
}

编辑：

我刚刚在 Github (link) 上创建了一个名为 Swift3PhoneTest 的示例项目，它演示了如何使用 NSSecureCoding 保存自定义数据容器对象。

它同时具有非可选和可选属性，并在可选属性为 nil 时正确管理归档和取消归档。

Encode/Decoding 在 Swift 3 中与 NSCoder 约会？

Encode/Decoding Date with NSCoder in Swift 3?

nscoder

ios

swift

编辑：