swift - 将状态保存在用户默认值中

Question

我有一个类可以保存某些东西的状态，在我的例子中是 ViewController 的一些变量，但有时它会加载错误或旧的数据，但我不明白为什么。

也许有人可以看一下我的代码，看看它是否有意义。

class TopFlopState: Codable, PersistenceState {

    var group: Groups = .large {
        didSet {
            save()
        }
    }
    var base: Bases = .usd {
        didSet {
            save()
        }
    }
    var valueOne: StatIntervalBaseModel = StatIntervalBaseModel(stat: "ppc", interval: "24h", base: "usd") {
        didSet {
            save()
        }
    }

    init(){
        let savedValues = load()
        if savedValues != nil {
            self.group = savedValues!.group
            self.base = savedValues!.base
            self.valueOne = savedValues!.valueOne
        }
    }
}

这是 PersistenceState 协议(protocol):

/**
Saves and Loads the class, enum etc. with UserDefaults.
Has to conform to Codable.
Uses as Key, the name of the class, enum etc.

 */
protocol PersistenceState  {
}


extension PersistenceState where Self: Codable {


    private var keyUserDefaults: String {
        return String(describing: self)
    }

    func save() {
        saveUserDefaults(withKey: keyUserDefaults, myType: self)
    }

    func load() -> Self? {
        return loadUserDefaults(withKey: keyUserDefaults)
    }

    private func saveUserDefaults<T: Codable>(withKey key: String, myType: T){
        do {
            let data = try PropertyListEncoder().encode(myType)
            UserDefaults.standard.set(data, forKey: key)
            print("Saved for Key:", key)
        } catch {
            print("Save Failed")
        }
    }

    private func loadUserDefaults<T: Codable>(withKey key: String) -> T? {
        guard let data = UserDefaults.standard.object(forKey: key) as? Data else { return nil }
        do {
            let decoded = try PropertyListDecoder().decode(T.self, from: data)
            return decoded
        } catch {
            print("Decoding failed for key", key)
            return nil
        }
    }
}

如果一个值被设置为它应该自动保存的值，但就像我设置的那样，有时它会保存正确的值但加载错误的值......

Answer 1

在我看来，它返回缓存。因为在 Apple official documentation ，它指出

UserDefaults caches the information to avoid having to open the user’s defaults database each time you need a default value

也许您可以更改流程、何时保存数据。在您的代码中显示您在 init() 中调用了 save() 3 次。