使用Swift将可编码的结构保存到UserDefaults [英] Saving a Codable Struct to UserDefaults with Swift

问题描述

我正在尝试对结构进行编码

I am trying to encode a struct

struct Configuration : Encodable, Decodable {
    private enum CodingKeys : String, CodingKey {
        case title = "title"
        case contents = "contents"
    }
    var title : String?
    var contents: [[Int]]?
}

转换为JSON以存储在UserDefaults.standard的本地密钥中.我有以下代码:

into JSON to store in a local key of UserDefaults.standard. I have the following code:

let jsonString = Configuration(title: nameField.text, contents: newContents)
let info = ["row" as String: jsonString as Configuration]
print("jsonString = \(jsonString)")
//trying to save object
let defaults = UserDefaults.standard
let recode = try! JSONEncoder().encode(jsonString)
defaults.set(recode, forKey: "simulationConfiguration")
//end of saving local

打印返回:

jsonString = Configuration(title: Optional("config"), contents: Optional([[4, 5], [5, 5], [6, 5]]))

所以我相信我正确地创建了对象.但是，当我下次尝试运行模拟器时尝试检索密钥时，我什么也没得到.我将以下内容放入AppDelegate中，它始终返回No Config.

so I believe I am creating the object correctly. However, when I try and retrieve the key the next time I run the simulator I get nothing. I put the following in AppDelegate and it always returns No Config.

let defaults = UserDefaults.standard
        let config = defaults.string(forKey: "simulationConfiguration") ?? "No Config"
        print("from app delegate = \(config.description)")

有什么想法吗?谢谢

推荐答案

在这里您要保存 Data 值(正确)

Here you are saving a Data value (which is correct)

defaults.set(recode, forKey: "simulationConfiguration")

但是这里您正在阅读 String

defaults.string(forKey: "simulationConfiguration")

您无法保存数据，无法读取 String 并期望它能正常工作.

You cannot save Data, read String and expect it to work.

首先，您不需要手动指定编码键.所以你的结构就变成这样

First of all you don't need to manually specify the Coding Keys. So your struct become simply this

struct Configuration : Codable {
    var title : String?
    var contents: [[Int]]?
}

保存

现在这是保存它的代码

Saving

Now here's the code for saving it

let configuration = Configuration(title: "test title", contents: [[1, 2, 3]])
if let data = try? JSONEncoder().encode(configuration) {
    UserDefaults.standard.set(data, forKey: "simulationConfiguration")
}

加载

这是读取它的代码

Loading

And here's the code for reading it

if
    let data = UserDefaults.standard.value(forKey: "simulationConfiguration") as? Data,
    let configuration = try? JSONDecoder().decode(Configuration.self, from: data) {
    print(configuration)
}

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