用户默认值未将字典内容快速保存3 [英] User Defaults not saving dictionary contents in swift 3

问题描述

我正在尝试向字典添加键和值，然后将用户默认的字典添加到字典中，并读回字典对象.我有两个问题，我真的很感谢您的帮助，

I am trying to add a key and a value to a dictionary then add this dictionary the user defaults and read back into a dictionary object. I have two questions that I would really appreciate any help in,

1)为什么从用户默认值读取的字典为空?由于我在字典中添加了键和值，因此不应该将这些键和值保存到我从用户默认值中检索的字典中吗?

1) why is the dictionary being read from user defaults empty? Since I added a key and a value to the dictionary shouldn't those be saved to the dictionary I retrieve from user defaults?

let defaults = UserDefaults.standard;
var myDict = [String: String]()
myDict["key"] = "value"

defaults.setValue(myDict, forKey: "myDict")


let mydict2 = defaults.object(forKey: "myDict") as? [String: String] ?? [String:String]()
print(mydict2)

2)如果字典将我创建的自定义类存储为值或键，那么该字典该怎么办?

2) What can I do to this code if the dictionary stores a custom class that I created as a value or a key so if the dictionary was like this:

class Car {
  var engineSize: Int
  var color: String

  init() {
    engineSize = 2000
    color = "blue"
  }

}

class Boat {    
  var surfaceArea: Int
  var weight: Int

  init() {    
    surfaceArea = 3500
    weight = 4000
  }
}

var myDict = [Car: Boat]()

如何将第二个字典保存为用户默认值并从中读取它?

how can I save that second dict to user defaults and read it from there?

谢谢

这是ebby94建议的答案:

This is the answer suggested by ebby94:

var myDict = [String:String]()
myDict["key"] = "value";

let data = NSKeyedArchiver.archivedData(withRootObject: myDict)
UserDefaults.standard.set(data, forKey: "myDict")


func foo()

{
  guard let archivedData = UserDefaults.standard.value(forKey: "myDict") as? Data
    else
    {
        print("failed1")
        return
    }
  guard var unarchivedDictionary = NSKeyedUnarchiver.unarchiveObject(with: archivedData) as? [String:String]
    else
    {
        print("failed2")
        return
    }

    print(unarchivedDictionary["key"]!)
}

foo()

但是此打印失败1，我假设数据没有正确存档.可能是因为我在操场上跑步吗?

However this prints failed1, I'm assuming the data wasn't archived correctly. Can this be because I'm running it in playground?

推荐答案

如果要将自定义对象保存到userDefault，首先需要对&解码变量，然后使用存档和amp;保存使用非存档获取数据.

If you want to save custom object to userDefault first you need to encode & decode variable then save using archive & get data using unarchive.

class Car {
    var engineSize: Int
    var color: String

    init() {
        engineSize = 2000
        color = "blue"
    }
    // Decode
    required convenience public init(coder decoder: NSCoder)
    {
        self.init()

        if let engineSize = decoder.decodeObject(forKey: "engineSize") as? Int
        {
            self.engineSize = engineSize
        }
        if let color = decoder.decodeObject(forKey: "color") as? String
        {
            self.color = color
        }
    }

    // Encode
    func encodeWithCoder(coder : NSCoder)
    {
        if let engineSize = self.engineSize
        {
            coder.encode(engineSize, forKey: "engineSize")
        }
        if let color = self.color
        {
            coder.encode(color, forKey: "weight")
        }
    }
}

class Boat {
    var surfaceArea: Int
    var weight: Int

    init() {
        surfaceArea = 3500
        weight = 4000
    }

    // Decode
    required convenience public init(coder decoder: NSCoder)
    {
        self.init()

        if let surfaceArea = decoder.decodeObject(forKey: "surfaceArea") as? Int
        {
            self.surfaceArea = surfaceArea
        }
        if let weight = decoder.decodeObject(forKey: "weight") as? Int
        {
            self.weight = weight
        }
    }

    // Encode
    func encodeWithCoder(coder : NSCoder)
    {
        if let surfaceArea = self.surfaceArea
        {
            coder.encode(surfaceArea, forKey: "surfaceArea")
        }
        if let weight = self.weight
        {
            coder.encode(weight, forKey: "weight")
        }
    }

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