在 UserDefaults 中存储自定义对象数组

Question

我花了很长时间试图弄清楚如何在 UserDefaults 中存储我的自定义结构数组。

这是我的代码：

struct DomainSchema: Codable {
    var domain: String
    var schema: String
}

var domainSchemas: [DomainSchema] {
    get {
        if UserDefaults.standard.object(forKey: "domainSchemas") != nil {
            let data = UserDefaults.standard.value(forKey: "domainSchemas") as! Data
            let domainSchema = try? PropertyListDecoder().decode(DomainSchema.self, from: data)
            
            return domainSchema!
        }
        
        return nil
    }
    
    set {
        UserDefaults.standard.set(try? PropertyListEncoder().encode(newValue), forKey: "domainSchemas")
    }
}

struct SettingsView: View {
    var body: some View {
        VStack {
            ForEach(domainSchemas, id: \.domain) { domainSchema in
                HStack {
                    Text(domainSchema.domain)
                    Text(domainSchema.schema)
                }
            }
            
            // clear history button
        }
        .onAppear {
            if (domainSchemas.isEmpty) {
                domainSchemas.append(DomainSchema(domain: "reddit.com", schema: "apollo://"))
            }
        }
    }
}

它给了我这些错误：

无法将类型“DomainSchema”的返回表达式转换为返回类型“[DomainSchema]”

“nil”与返回类型“[DomainSchema]”不兼容

我不太确定如何获取对象数组而不是单个对象，或者如何解决nil不兼容错误......

Answer 1

如果您确实想使用 UserDefaults 保存数据，最简单的方法是使用一个类并使其符合 NSCoding。关于您的全局 var domainSchemas，我建议使用单例或扩展 UserDefaults 并为其创建一个计算属性：

class DomainSchema: NSObject, NSCoding {
    var domain: String
    var schema: String
    init(domain: String, schema: String) {
        self.domain = domain
        self.schema = schema
    }
    required init(coder decoder: NSCoder) {
        self.domain = decoder.decodeObject(forKey: "domain") as? String ?? ""
        self.schema = decoder.decodeObject(forKey: "schema") as? String ?? ""
    }
    func encode(with coder: NSCoder) {
        coder.encode(domain, forKey: "domain")
        coder.encode(schema, forKey: "schema")
    }
}

extension UserDefaults {
    var domainSchemas: [DomainSchema] {
        get {
            guard let data = UserDefaults.standard.data(forKey: "domainSchemas") else { return [] }
            return (try? NSKeyedUnarchiver.unarchiveTopLevelObjectWithData(data)) as? [DomainSchema] ?? []
        }
        set {
            UserDefaults.standard.set(try? NSKeyedArchiver.archivedData(withRootObject: newValue, requiringSecureCoding: false), forKey: "domainSchemas")
        }
    }
}

用法：

UserDefaults.standard.domainSchemas = [.init(domain: "a", schema: "b"), .init(domain: "c", schema: "d")]

UserDefaults.standard.domainSchemas  // [{NSObject, domain "a", schema "b"}, {NSObject, domain "c", schema "d"}]

如果您更喜欢使用 Codable 方法来使用 UserDefaults 保存数据：

struct DomainSchema: Codable {
    var domain: String
    var schema: String
    init(domain: String, schema: String) {
        self.domain = domain
        self.schema = schema
    }
}

extension UserDefaults {
    var domainSchemas: [DomainSchema] {
        get {
            guard let data = UserDefaults.standard.data(forKey: "domainSchemas") else { return [] }
            return (try? PropertyListDecoder().decode([DomainSchema].self, from: data)) ?? []
        }
        set {
            UserDefaults.standard.set(try? PropertyListEncoder().encode(newValue), forKey: "domainSchemas")
        }
    }
}

用法：

UserDefaults.standard.domainSchemas = [.init(domain: "a", schema: "b"), .init(domain: "c", schema: "d")]

UserDefaults.standard.domainSchemas  // [{domain "a", schema "b"}, {domain "c", schema "d"}]

我认为最好的选择是不使用 UserDefaults，创建一个单例“共享实例”，在那里声明一个 domainSchemas 属性并将 json 数据保存在应用程序支持目录的子目录中：

extension URL {
    static var domainSchemas: URL {
        let applicationSupport = FileManager.default.urls(for: .applicationSupportDirectory, in: .userDomainMask).first!
        let bundleID = Bundle.main.bundleIdentifier ?? "company name"
        let subDirectory = applicationSupport.appendingPathComponent(bundleID, isDirectory: true)
        try? FileManager.default.createDirectory(at: subDirectory, withIntermediateDirectories: true, attributes: nil)
        return subDirectory.appendingPathComponent("domainSchemas.json")
    }
}

class Shared {
    static let instance = Shared()
    private init() { }
    var domainSchemas: [DomainSchema] {
        get {
            guard let data = try? Data(contentsOf: .domainSchemas) else { return [] }
            return (try? JSONDecoder().decode([DomainSchema].self, from: data)) ?? []
        }
        set {
            try? JSONEncoder().encode(newValue).write(to: .domainSchemas)
        }
    }
}

用法：

Shared.instance.domainSchemas = [.init(domain: "a", schema: "b"), .init(domain: "c", schema: "d")]

Shared.instance.domainSchemas  // [{domain "a", schema "b"}, {domain "c", schema "d"}]