Swift 正在从 UserDefaults 保存和检索自定义对象

Question

我在游乐场使用 Swift 3, Xcode 8.0:

import Foundation
class Person: NSObject, NSCoding {
    var name: String
    var age: Int
    init(name: String, age: Int) {
        self.name = name
        self.age = age
    }
    required convenience init(coder aDecoder: NSCoder) {
        let name = aDecoder.decodeObject(forKey: "name") as! String
        let age = aDecoder.decodeObject(forKey: "age") as! Int
        self.init(
            name: name,
            age: age
        )
    }
    func encode(with aCoder: NSCoder) {
        aCoder.encode(name, forKey: "name")
        aCoder.encode(age, forKey: "age")
    }
}

创建人物数组

let newPerson = Person(name: "Joe", age: 10)
var people = [Person]()
people.append(newPerson)

编码数组

let encodedData = NSKeyedArchiver.archivedData(withRootObject: people)
print("encodedData: \(encodedData))")

保存到用户默认值

let userDefaults: UserDefaults = UserDefaults.standard()
userDefaults.set(encodedData, forKey: "people")
userDefaults.synchronize()

检查

print("saved object: \(userDefaults.object(forKey: "people"))")

从 userDefaults 中检索

if let data = userDefaults.object(forKey: "people") {
    let myPeopleList = NSKeyedUnarchiver.unarchiveObject(with: data as! Data)
    print("myPeopleList: \(myPeopleList)")
}else{
    print("There is an issue")
}

只需查看归档数据

if let myPeopleList = NSKeyedUnarchiver.unarchiveObject(with: encodedData){
   print("myPeopleList: \(myPeopleList)")
}else{
   print("There is an issue")
}

我无法将数据对象正确保存到 userDefaults，此外，底部的检查会产生错误：

Fatal error: Unexpectedly found nil while unwrapping an Optional value

“检查”行还显示保存的对象为零。这是我对象的 NSCoder 中的错误吗？

Answer 1

Swift 4 或更高版本

您可以再次save/test您在游乐场中的价值观

UserDefaults需要在真实项目中进行测试。注意：无需强制同步。如果你想在 playground 中测试 coding/decoding，你可以使用 keyed archiver 将数据保存到文档目录中的 plist 文件中。您还需要解决 class:

中的一些问题

class Person: NSObject, NSCoding {
    let name: String
    let age: Int
    init(name: String, age: Int) {
        self.name = name
        self.age = age
    }
    required init(coder decoder: NSCoder) {
        self.name = decoder.decodeObject(forKey: "name") as? String ?? ""
        self.age = decoder.decodeInteger(forKey: "age")
    }
    func encode(with coder: NSCoder) {
        coder.encode(name, forKey: "name")
        coder.encode(age, forKey: "age")
    }
}

测试：

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()

        do {
            // setting a value for a key
            let newPerson = Person(name: "Joe", age: 10)
            var people = [Person]()
            people.append(newPerson)
            let encodedData = try NSKeyedArchiver.archivedData(withRootObject: people, requiringSecureCoding: false)
            UserDefaults.standard.set(encodedData, forKey: "people")
            // retrieving a value for a key
            if let data = UserDefaults.standard.data(forKey: "people"),
                let myPeopleList = try NSKeyedUnarchiver.unarchiveTopLevelObjectWithData(data) as? [Person] {
                myPeopleList.forEach({print([=11=].name, [=11=].age)})  // Joe 10
            }                    
        } catch {
            print(error)
        }
        
    }
}

Answer 2

let age = aDecoder.decodeObject(forKey: "age") as! Int

已针对 Swift 3 进行更改；这不再适用于值类型。现在正确的语法是：

let age = aDecoder.decodeInteger(forKey: "age")

各种不同类型都有相关的 decode...() 函数：

let myBool = aDecoder.decodeBoolean(forKey: "myStoredBool")
let myFloat = aDecoder.decodeFloat(forKey: "myStoredFloat")

编辑：Full list of all possible decodeXXX functions in Swift 3

编辑：

另一个重要说明：如果您以前保存过使用旧版本 Swift 编码的数据，则这些值必须使用 decodeObject() 进行解码，然而一旦你使用 encode(...) 重新编码数据，如果它是一个值类型，它就不能再用 decodeObject() 解码。因此，Markus Wyss 的回答将允许您处理使用 Swift 版本编码数据的情况：

self.age = aDecoder.decodeObject(forKey: "age") as? Int ?? aDecoder.decodeInteger(forKey: "age")

Answer 3

试试这个：

self.age = aDecoder.decodeObject(forKey: "age") as? Int ?? aDecoder.decodeInteger(forKey: "age")

Answer 4

在Swift 4:

您可以使用 Codable 从 Userdefaults 中保存和检索自定义对象。如果你经常这样做，那么你可以添加为扩展并像下面那样使用它。

extension UserDefaults {

   func save<T:Encodable>(customObject object: T, inKey key: String) {
       let encoder = JSONEncoder()
       if let encoded = try? encoder.encode(object) {
           self.set(encoded, forKey: key)
       }
   }

   func retrieve<T:Decodable>(object type:T.Type, fromKey key: String) -> T? {
       if let data = self.data(forKey: key) {
           let decoder = JSONDecoder()
           if let object = try? decoder.decode(type, from: data) {
               return object
           }else {
               print("Couldnt decode object")
               return nil
           }
       }else {
           print("Couldnt find key")
           return nil
       }
   }

}

您的 Class 必须遵循 Codable。它只是可编码和可解码协议的类型别名。

class UpdateProfile: Codable {
  //Your stuffs
}

用法：

let updateProfile = UpdateProfile()

//To save the object
UserDefaults.standard.save(customObject: updateProfile, inKey: "YourKey")

//To retrieve the saved object
let obj = UserDefaults.standard.retrieve(object: UpdateProfile.self, fromKey: "YourKey")

有关更多编码和解码自定义类型，请查看 Apple's documentation。

Answer 5

在 Swift 5 中，我将使用属性包装器来简化代码：

/// A type that adds an interface to use the user’s defaults with codable types
///
/// Example:
/// ```
/// @UserDefaultCodable(key: "nameKey", defaultValue: "Root") var name: String
/// ```
/// Adding the attribute @UserDefaultCodable the property works reading and writing from user's defaults
/// with any codable type
///
@propertyWrapper public struct UserDefaultCodable<T: Codable> {
    private let key: String
    private let defaultValue: T

    /// Initialize the key and the default value.
    public init(key: String, defaultValue: T) {
        self.key = key
        self.defaultValue = defaultValue
    }

    public var wrappedValue: T {
        get {
            // Read value from UserDefaults
            guard let data = UserDefaults.standard.object(forKey: key) as? Data else {
                // Return defaultValue when no data in UserDefaults
                return defaultValue
            }

            // Convert data to the desire data type
            let value = try? JSONDecoder().decode(T.self, from: data)
            return value ?? defaultValue
        }
        set {
            // Convert newValue to data
            let data = try? JSONEncoder().encode(newValue)

            // Set value to UserDefaults
            UserDefaults.standard.set(data, forKey: key)
        }
    }
}

Swift 正在从 UserDefaults 保存和检索自定义对象

Swift saving and retrieving custom object from UserDefaults

ios

swift

xcode

swift3

nscoding