我想将从CoreML预测的MLMultiArray数据存储到本地文件中，因为Core Data不支持这种类型，所以我试用了NSKeyedUnarchiver，因为MLMultiArray符合NSObject。
但是，此对象可以是encode并成功保存，但不能是正确的decode。

error is: Error Domain=NSCocoaErrorDomain Code=4864 "value for key 'embedding' was of unexpected class 'MLMultiArray' (0x1e35d84b8) [/System/Library/Frameworks/CoreML.framework].
Allowed classes are:
 {(
    "'CoreMLApp.Embedding' (0x1002a53f8) [/private/var/containers/Bundle/Application/C86A850C-27F6-43CB-82AF-9223/CoreMLApp.app]",
    "'NSArray' (0x1e3380b50) [/System/Library/Frameworks/CoreFoundation.framework]"
)}" UserInfo={NSDebugDescription=value for key 'embedding' was of unexpected class 'MLMultiArray' (0x1e35d84b8)

下面是我的对象：

class Embedding: NSObject, NSSecureCoding {
    static var supportsSecureCoding: Bool = true
  
    var id: String?
    var embedding: MLMultiArray?
    
    init(id: String, embedding: MLMultiArray) {
        self.id = id
        self.embedding = embedding
    }
    
    func encode(with aCoder: NSCoder) {
        aCoder.encode(self.id, forKey: "id")
        aCoder.encode(self.embedding, forKey: "embedding")
    }
    
    required init?(coder aDecoder: NSCoder) {
        self.id = aDecoder.decodeObject(forKey: "id") as? String
        self.embedding = aDecoder.decodeObject(forKey: "embedding") as? MLMultiArray
    }
}

编解码部分：

private func saveEmbeddingsData(embeddings: [Embedding], fileName: String) -> Bool {
        let filePath = self.getDocumentsDirectory().appendingPathComponent(fileName)
        do {
            let data = try NSKeyedArchiver.archivedData(withRootObject: embeddings, requiringSecureCoding: true)
            try data.write(to: filePath)
            return true
        } catch {
            print("error is: \(error.localizedDescription)")
        }
        return false
    }

    private func loadEmbeddingsData(fileName: String) -> [Embedding]? {
        let filePath = self.getDocumentsDirectory().appendingPathComponent(fileName)
        do {
            let data = try Data(contentsOf: filePath)
            let embeddings = try NSKeyedUnarchiver.unarchivedArrayOfObjects(ofClasses: [Embedding.self], from: data) as? [Embedding]
            return embeddings
        } catch {
            print("error is: \(String(describing: error))")
        }
        return nil
    }
    
    private func getDocumentsDirectory() -> URL {
        let arrayPaths = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)
        return arrayPaths[0]
    }

我尝试使用NSCoding而不是NSSecureCoding，但是所有NSKeyedUnarchiver.unarchiveXXX方法都输出错误，要求数据符合NSSecureCoding。