Question

我正在尝试从捆绑包中的json文件中读取数据，并且要实现这一点，我创建了一个protocol ReadableJSONFile，它具有fileName来存储json文件名和readFromJSONFile()解码文件

public protocol ReadableJSONFile {

    /// The name of your json file in the bundle
    var fileName: String { get }

    func readFromJSONFile() -> Self
}

和

public extension ReadableJSONFile where Self: Codable {

    var fileName: String {
        return "\(String(describing: Self.self)).json"
    }

    func readFromJSONFile() -> Self {
        guard let url = Bundle.main.url(forResource: fileName, withExtension: nil) else {
            fatalError("Failed to locate \(fileName) in app bundle.")
        }
        guard let data = try? Data(contentsOf: url) else {
            fatalError("Failed to load \(fileName) in app bundle.")
        }

        let decoder = JSONDecoder()

        guard let loaded = try? decoder.decode(Self.self, from: data) else {
            fatalError("Failed to decode \(fileName) from app bundle.")
        }
        return loaded
    }
}

我编写了这个简单的json文件，并将其命名为ModelA.json

{
    "color": "yellow",
    "name": "Mike"
}

然后创建此模型来表示ModelA.json文件

struct ModelA: Codable, ReadableJSONFile {

    let color: String
    let name: String
}

在我的视图控制器中，我有以下代码行

class ViewController: UIViewController {

    let data = ModelA.readFromJSONFile() // Here an error saying "Instance member 'readFromJSONFile' cannot be used on type 'ModelA'; did you mean to use a value of this type instead?"

    override func viewDidLoad() {
        super.viewDidLoad()
        print(data.name)
    }

}

当我将fileName和readFromJSONFile()设为static时，一切正常，但是当我这样做时，我无法覆盖fileName内部的ModelA确认为ReadableJSONFile

Answer 1

您无法访问不是类型成员的类成员，而您需要像我在下面创建的那样创建类的对象（实例），

class ViewController: UIViewController {

    let instance = ModelA()
    let data = instance.readFromJSONFile() 

    override func viewDidLoad() {
        super.viewDidLoad()
        print(data.name)
    }

}

Swift错误提示`实例成员*不能在类型上使用

1 个答案: