मैं अपनी संरचना को सहेजने और लोड करने के लिए UserDefaults का उपयोग कैसे करूं?

इसे डिज़ाइन करने का एक अच्छा तरीका सहायक विधियों की एक जोड़ी के साथ विस्तार UserDefaults करना है:

extension UserDefaults {

    func set<T: Encodable>(codable: T, forKey key: String) {
        let encoder = JSONEncoder()
        do {
            let data = try encoder.encode(codable)
            let jsonString = String(data: data, encoding: .utf8)!
            print("Saving \"\(key)\": \(jsonString)")
            self.set(jsonString, forKey: key)
        } catch {
            print("Saving \"\(key)\" failed: \(error)")
        }
    }

    func codable<T: Decodable>(_ codable: T.Type, forKey key: String) -> T? {
        guard let jsonString = self.string(forKey: key) else { return nil }
        guard let data = jsonString.data(using: .utf8) else { return nil }
        let decoder = JSONDecoder()
        print("Loading \"\(key)\": \(jsonString)")
        return try? decoder.decode(codable, from: data)
    }
}

फिर इसे QuotesViewController में इस तरह इस्तेमाल करें:

class QuotesViewController: UIViewController {

    struct RandomItems: Codable {
        var items : [String]
        var seen  = 0

        init(items:[String], seen: Int) {
            self.items = items
            self.seen = seen
        }

        init(_ items: [String]) {
            self.init(items: items, seen: 0)
        }
    }

    var quotes: RandomItems! = RandomItems([
        "James",
        "John",
        "William",
    ])

    override func viewDidAppear(_ animated: Bool) {
        // Code to load the struct again after the view appears.
        let defaults = UserDefaults.standard
        quotes = defaults.codable(RandomItems.self, forKey: "quotes")
    }

    override func viewWillDisappear(_ animated: Bool) {
        // Code to save struct before the view disappears.
        let defaults = UserDefaults.standard
        if let quotes = quotes {
            defaults.set(codable: quotes, forKey: "quotes")
        }
    }
}

उपरोक्त दृश्य नियंत्रक प्रिंट दर्ज करना (और बाहर निकलना):

"उद्धरण" सहेजा जा रहा है: {"आइटम": ["जेम्स", "जॉन", "विलियम"], "देखा": 0}
लोड हो रहा है "उद्धरण": {"आइटम": ["जेम्स", "जॉन", "विलियम"], "देखा": 0}

अपडेट करें। इसके लायक क्या है, नीचे पूर्ण कोड है जिसका उपयोग मैंने Xcode 9 खेल के मैदान में इसका परीक्षण करने के लिए किया था:

import Foundation

extension UserDefaults {

    func set<T: Encodable>(codable: T, forKey key: String) {
        let encoder = JSONEncoder()
        do {
            let data = try encoder.encode(codable)
            let jsonString = String(data: data, encoding: .utf8)!
            print("Saving \"\(key)\": \(jsonString)")
            self.set(jsonString, forKey: key)
        } catch {
            print("Saving \"\(key)\" failed: \(error)")
        }
    }

    func codable<T: Decodable>(_ codable: T.Type, forKey key: String) -> T? {
        guard let jsonString = self.string(forKey: key) else { return nil }
        guard let data = jsonString.data(using: .utf8) else { return nil }
        let decoder = JSONDecoder()
        print("Loading \"\(key)\": \(jsonString)")
        return try? decoder.decode(codable, from: data)
    }
}

class UIViewController: NSObject {
    func viewDidAppear(_ animated: Bool) { }
    func viewWillDisappear(_ animated: Bool) { }
}

class QuotesViewController: UIViewController {

    struct RandomItems: Codable {
        var items : [String]
        var seen  = 0

        init(items:[String], seen: Int) {
            self.items = items
            self.seen = seen
        }

        init(_ items: [String]) {
            self.init(items: items, seen: 0)
        }
    }

    var quotes: RandomItems! = RandomItems([
        "James",
        "John",
        "William",
        "Mary",
        "Sarah",
        "Michael",
        "Steve",
        "Lisa",
        "Jeff",
        "Chris",
        ])

    override func viewDidAppear(_ animated: Bool) {
        // Code to load the struct again after the view appears.
        let defaults = UserDefaults.standard
        quotes = defaults.codable(RandomItems.self, forKey: "quotes")
    }

    override func viewWillDisappear(_ animated: Bool) {
        // Code to save struct before the view disappears.
        let defaults = UserDefaults.standard
        if let quotes = quotes {
            defaults.set(codable: quotes, forKey: "quotes")
        }
    }
}

let vc = QuotesViewController()

vc.viewWillDisappear(false)
vc.quotes = nil

vc.viewDidAppear(true)
print(vc.quotes)