Ios 核心数据中的安全编码测量类，NSValueTransformers

我有一个应用程序，大量使用测量。它是用SwiftUI/iOS 14编写的。我将数据保存在核心数据数据库中。在我尝试实现安全编码之前，该应用程序运行良好。我制作了一个示例应用程序，除去基本的东西。它基于Xcode的默认核心数据应用程序，几乎没有改动。同样，在我尝试使用安全编码之前，我可以很好地保存度量

xddatamodel

以及错误如下：

我正在为实体使用手动codegen，它如下所示：

extension Item {

    @nonobjc public class func fetchRequest() -> NSFetchRequest<Item> {
        return NSFetchRequest<Item>(entityName: "Item")
    }

    @NSManaged public var timestamp_: Date?
    @NSManaged private var notes_: String?
    @NSManaged private var length_: Measurement<UnitLength>?

    public var timestamp: Date {
        get { timestamp_ ?? Date(timeIntervalSince1970: 0) }
        set { timestamp_ = newValue }
    }

    public var notes: String {
        get { notes_ ?? "Add Notes Here..." }
        set { notes_ = newValue }
    }

    public var length: Measurement<UnitLength> {
        get { length_ ?? Measurement(value: 0, unit: UnitLength.meters) }
        set { length_ = newValue }
    }

}

@objc(UnitLengthValueTransformer)
final class UnitLengthValueTransformer: NSSecureUnarchiveFromDataTransformer {
    static let name = NSValueTransformerName(rawValue: String(describing: UnitLengthValueTransformer.self))
    override static var allowedTopLevelClasses: [AnyClass] {
        return [UnitLength.self]
    }
    
    public static func register() {
        let transformer = UnitLengthValueTransformer()
        ValueTransformer.setValueTransformer(transformer, forName: name)
    }
}

extension Item {
      public var length: Measurement<UnitLength> {
        // The getter returns an actual value, not an optional. If you want to return an optional, just use:
        // get { length_ as Measurement<UnitLength> }
        get { length_ as Measurement<UnitLength>? ?? Measurement(value: 0, unit: UnitLength.meters) }
        set { length_ = newValue as NSMeasurement }
    }

}

我的ValueTransformer如下所示：

extension Item {

    @nonobjc public class func fetchRequest() -> NSFetchRequest<Item> {
        return NSFetchRequest<Item>(entityName: "Item")
    }

    @NSManaged public var timestamp_: Date?
    @NSManaged private var notes_: String?
    @NSManaged private var length_: Measurement<UnitLength>?

    public var timestamp: Date {
        get { timestamp_ ?? Date(timeIntervalSince1970: 0) }
        set { timestamp_ = newValue }
    }

    public var notes: String {
        get { notes_ ?? "Add Notes Here..." }
        set { notes_ = newValue }
    }

    public var length: Measurement<UnitLength> {
        get { length_ ?? Measurement(value: 0, unit: UnitLength.meters) }
        set { length_ = newValue }
    }

}

@objc(UnitLengthValueTransformer)
final class UnitLengthValueTransformer: NSSecureUnarchiveFromDataTransformer {
    static let name = NSValueTransformerName(rawValue: String(describing: UnitLengthValueTransformer.self))
    override static var allowedTopLevelClasses: [AnyClass] {
        return [UnitLength.self]
    }
    
    public static func register() {
        let transformer = UnitLengthValueTransformer()
        ValueTransformer.setValueTransformer(transformer, forName: name)
    }
}

extension Item {
      public var length: Measurement<UnitLength> {
        // The getter returns an actual value, not an optional. If you want to return an optional, just use:
        // get { length_ as Measurement<UnitLength> }
        get { length_ as Measurement<UnitLength>? ?? Measurement(value: 0, unit: UnitLength.meters) }
        set { length_ = newValue as NSMeasurement }
    }

}

据我所知，存在分歧，UnitLength的类标题为：

open class UnitLength : Dimension, NSSecureCoding 

因此，它确实符合NSSecureCodeding

我使用了以下参考资料：

我仍然会遇到同样的错误：

Fatal error: Unresolved error Error Domain=NSCocoaErrorDomain Code=134060 "A Core Data error occurred.", [:]: file Core_Data_Test/ContentView.swift, line 57

---

我不知道我做错了什么导致了这次撞车。

多亏了@LeoDabus，我终于能够解决这个问题。关键是将Swift测量转换为NSMEASURATION，并在核心数据中使用NSMEASURATION。您需要将自定义类设置为

NSMeasurement

。您的转换器将是自定义值转换器。我打电话给我的

NSMeasurementValueTransformer

。您的.xcdatamodeld将如下所示：

extension Item {

    @nonobjc public class func fetchRequest() -> NSFetchRequest<Item> {
        return NSFetchRequest<Item>(entityName: "Item")
    }

    @NSManaged public var timestamp_: Date?
    @NSManaged private var notes_: String?
    @NSManaged private var length_: Measurement<UnitLength>?

    public var timestamp: Date {
        get { timestamp_ ?? Date(timeIntervalSince1970: 0) }
        set { timestamp_ = newValue }
    }

    public var notes: String {
        get { notes_ ?? "Add Notes Here..." }
        set { notes_ = newValue }
    }

    public var length: Measurement<UnitLength> {
        get { length_ ?? Measurement(value: 0, unit: UnitLength.meters) }
        set { length_ = newValue }
    }

}

@objc(UnitLengthValueTransformer)
final class UnitLengthValueTransformer: NSSecureUnarchiveFromDataTransformer {
    static let name = NSValueTransformerName(rawValue: String(describing: UnitLengthValueTransformer.self))
    override static var allowedTopLevelClasses: [AnyClass] {
        return [UnitLength.self]
    }
    
    public static func register() {
        let transformer = UnitLengthValueTransformer()
        ValueTransformer.setValueTransformer(transformer, forName: name)
    }
}

extension Item {
      public var length: Measurement<UnitLength> {
        // The getter returns an actual value, not an optional. If you want to return an optional, just use:
        // get { length_ as Measurement<UnitLength> }
        get { length_ as Measurement<UnitLength>? ?? Measurement(value: 0, unit: UnitLength.meters) }
        set { length_ = newValue as NSMeasurement }
    }

}

我将自定义值转换器定义为：

@objc(NSMeasurementValueTransformer)
final class NSMeasurementValueTransformer: NSSecureUnarchiveFromDataTransformer {
    static let name = NSValueTransformerName(rawValue: String(describing: NSMeasurementValueTransformer.self))
    override static var allowedTopLevelClasses: [AnyClass] {
        return [NSMeasurement.self]
    }
    
    public static func register() {
        let transformer = NSMeasurementValueTransformer()
        ValueTransformer.setValueTransformer(transformer, forName: name)
    }
}

有趣的是，我不必注册值转换器。也许有人能解释为什么，但它不需要注册就可以工作

最后，在一个扩展中，我声明了一个面向公众的变量，该变量处理从和到我想要使用的度量的变量转换，如下所示：

extension Item {

    @nonobjc public class func fetchRequest() -> NSFetchRequest<Item> {
        return NSFetchRequest<Item>(entityName: "Item")
    }

    @NSManaged public var timestamp_: Date?
    @NSManaged private var notes_: String?
    @NSManaged private var length_: Measurement<UnitLength>?

    public var timestamp: Date {
        get { timestamp_ ?? Date(timeIntervalSince1970: 0) }
        set { timestamp_ = newValue }
    }

    public var notes: String {
        get { notes_ ?? "Add Notes Here..." }
        set { notes_ = newValue }
    }

    public var length: Measurement<UnitLength> {
        get { length_ ?? Measurement(value: 0, unit: UnitLength.meters) }
        set { length_ = newValue }
    }

}

@objc(UnitLengthValueTransformer)
final class UnitLengthValueTransformer: NSSecureUnarchiveFromDataTransformer {
    static let name = NSValueTransformerName(rawValue: String(describing: UnitLengthValueTransformer.self))
    override static var allowedTopLevelClasses: [AnyClass] {
        return [UnitLength.self]
    }
    
    public static func register() {
        let transformer = UnitLengthValueTransformer()
        ValueTransformer.setValueTransformer(transformer, forName: name)
    }
}

extension Item {
      public var length: Measurement<UnitLength> {
        // The getter returns an actual value, not an optional. If you want to return an optional, just use:
        // get { length_ as Measurement<UnitLength> }
        get { length_ as Measurement<UnitLength>? ?? Measurement(value: 0, unit: UnitLength.meters) }
        set { length_ = newValue as NSMeasurement }
    }

}

扩展项{
公共变量长度：度量{
//getter返回的是实际值，而不是可选值。如果要返回可选值，只需使用：
//获取{length_uu作为度量值}
获取{length_uu作为度量值？？？度量值（值：0，单位：UnitLength.meters）}
将{length\=newValue设置为NSMeasurement}
}
}

您将注意到，核心数据属性的名称为

length\uu

。我仍然可以在我的应用程序中使用Swift测量，但可以将它们安全地存储在核心数据中。这修复了核心数据警告：

CoreData：此应用程序中的一个或多个模型正在使用 具有未设置的转换器名称的可转换属性， 或者从DataTransformerName设置为NSKeyedUnachiveFromDataTransformerName。请转到 使用“NSSecureUnarchiveFromData”或 NSSecureUnarchiveFromDataTransformer。在某种程度上，核心数据 当为nil时，将默认使用“NSSecureUnarchiveFromData” 指定的，以及包含不包含 支持NSSecureCodeding将变得不可读

---

测量结果不符合要求NSSecureCoding@LeoDabus我检查过了，测量结果符合要求。有没有想过如何将其保存为NSMeasurement？NSMeasurement有，但Measurement没有