在UserDefaults中存储自定义对象的数组

如何解决在UserDefaults中存储自定义对象的数组

我想了解如何在UserDefaults中存储自定义结构的数组。

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://"))
            }
        }
    }
}

这给了我这些错误：

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

'nil'与返回类型'[DomainSchema]'

不兼容

我不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...

解决方法

如果您真的想使用UserDefaults持久化数据，最简单的方法是使用一个类并使它符合NSCoding。关于您的全局var domainSchemas，我建议使用单例或扩展UserDefaults并在那里为它创建一个计算属性：

---

<layout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools">

    <data>

        <variable
            name="viewmodel"
            type="com.example.android.databinding.basicsample.data.SimpleViewModelSolution"/>
    </data>

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <!-- A simple binding between a TextView and a string observable in the ViewModel -->
        <TextView
            android:id="@+id/name"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_marginStart="16dp"
            android:layout_marginTop="8dp"
            android:layout_marginEnd="128dp"
            android:text="@{viewmodel.name}"
...
}

---

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")
    }
}

---

用法：

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")
        }
    }
}

---

---

如果您更喜欢Codable方法，还可以使用UserDefaults来保留数据：

---

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"}]

---

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

---

用法：

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")
        }
    }
}

---

我认为最好的选择是不使用UserDefaults，创建单例“共享实例”，在其中声明domainSchemas属性并将json数据保存在应用程序支持目录的子目录中：

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

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

---

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")
    }
}

---

用法：

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)
        }
    }
}