Question

我刚刚开始学习SwiftUI。我哪里出错了？我正在尝试在我的课程（ManyItems）中添加可编码的一致性。这样，我最终可以使用JSON将数组保存到磁盘。两个错误：

1）在“必需的init（...）“ id = try ...”和编码函数中：“ try container.encode ...”导致中的“ id”不可用Swift：'id'在Swift中不可用；使用“任何””

2）在必需的init（...）和func编码中：“使用未解析的标识符'one'。” 我假定该结构中的标识符将被结转到类中？

struct Item: Identifiable {
    var id = UUID()
    var one: String
}

class ManyItems: ObservableObject, Codable {
    @Published var manyitems = [Item]()
    enum CodingKeys: CodingKey {
        case id
        case one
    }
    required init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        id = try container.decode(UUID.self, forKey: .id)
        one = try container.decode(String.self, forKey: .one)
    }
    func encode(to encoder: Encoder) throws {
        var container = encoder.container(keyedBy: CodingKeys.self)
        try container.encode(id, forKey: .id)
        try container.encode(one, forKey: .one)
    }
}

Answer 1

您的Codable模型应该是

struct Item: Codable, Identifiable {
    var id = UUID()
    var one: String
}

class ManyItems: Codable, ObservableObject {
    @Published var manyitems = [Item]()
}

从代码中可以明显看出，您没有处理任何特定的解析案例。因此，无需显式实现init(from:)和encode(to:)方法。

Answer 2

我找到了解决方案，但必须采取略有不同的方法。希望这可以帮助需要使用符合Codable和ObservableObject的Collection的其他人保存到Apps documentDirectory。

我使结构'Item'符合Codable（即不是类'ManyItem'）。我为JSON编码添加了代码，并将集合保存到Apps documentDirectory。属性值更改时，这会自动发生。该类通过从Apps文档目录中读取/解码JSON文件启动，或者如果JSON文件尚不可用，则作为新的空白实例启动。

struct Item: Identifiable, Codable {
    var id = UUID()
    var one: String    
}

class ManyItems: ObservableObject {
    @Published var manyitems: [Item] {
        didSet {
            // Saves the array 'items' to disc
            do {
                // find the documentDirectory and create an URL for the JSON
                file
                let filename = getDocumentsDirectory().appendingPathComponent("manyitems.json")
            let data = try JSONEncoder().encode(self.manyitems)
            try data.write(to: filename, options: [.atomicWrite])
        } catch {
            print("Unable to save data.")
        }
    }
}
init() {
    // replaces a call to 'getDocumentsDirectory()' methode as it created an initialisation error.
    let paths = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)
    // Add the first [0] path to the filename and create 'filename'
    let filename = paths[0].appendingPathComponent("manyitems.json")
    //print(filename)
    do {
        // Try to read the file (if it exist) and load the data into the array 'manyitem'
        let data = try Data(contentsOf: filename)
        manyitems = try JSONDecoder().decode([Item].self, from: data)
        // Yes all good then exit
        return
    } catch {
        // Something whent wrong. Initialize by creating an empty array 'manyitems'
        self.manyitems = []
        print("Unable to load saved data.")
    }
}
// retreives the App's first DocumentDirectory
func getDocumentsDirectory() -> URL {
    let paths = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)
    return paths[0]
}

}

SwiftUI使用'id'属性为{Published属性添加可编码一致性

2 个答案: