ios - 具有通用解码类型的网络调用

Question

我正在尝试创建一个通用网络功能我正在寻找一个 API 处理程序，该处理程序将从网络下载 JSON 并将主题转换为符合 Decodable 的 Swift 结构协议(protocol)。目前我正在使用显式类型:

struct MyObject : Decodable {
    let id   : Int
    let name : String
}

static fileprivate func makeNetworkRequest(url: URL, completionHandler: @escaping(_ error: Error?, _ myObject: MyObject?) -> ()) {
    URLSession.shared.dataTask(with: url) { (data, response, error) in
        // handle error
        do {
            let myNewObject = try JSONDecoder().decode(MyObject.self, from: data!)
            completionHandler(nil, myNewObject)
        }
        catch let error {
            completionHandler(error, nil)
            return
        }
    }.resume()
}

我希望创建一个通用函数，我可以在其中指定任何确认到 Decodable 的数据类型并在完成处理程序中返回数据对象。类似于以下内容:

static fileprivate func makeNetworkRequest<T>(url: URL, type: <<<Decodable Type>>>, completionHandler: @escaping(_ error: Error?, _ myObject: <<<Deocable Object>>>?) -> ()) {
    URLSession.shared.dataTask(with: url) { (data, response, error) in
        // handle error
        do {
            let myNewObject = try JSONDecoder().decode(<<<Decodable Type>>>.self, from: data!)
            completionHandler(nil, myNewObject)
        }
        catch let error {
            completionHandler(error, nil)
            return
        }
    }.resume()
}

但是，我似乎无法正确获取函数参数。我没有很多使用泛型的经验。任何帮助，将不胜感激

Answer 1

您可以模仿 decode 的声明JSONDecoder的方法:

open func decode<T>(_ type: T.Type, from data: Data) throws -> T where T : Decodable

将上面的模式应用到您的代码中，定义应该是这样的:

static fileprivate func makeNetworkRequest<T>(url: URL, type: T.Type, completionHandler: @escaping (_ error: Error?, _ myObject: T?) -> ())
where T: Decodable
{
    URLSession.shared.dataTask(with: url) { (data, response, error) in
        // handle error
        do {
            let myNewObject = try JSONDecoder().decode(T.self, from: data!)
            completionHandler(nil, myNewObject)
        } catch let error {
            completionHandler(error, nil)
            return
        }
    }.resume()
}

或者你可以这样写:

static fileprivate func makeNetworkRequest<T: Decodable>(url: URL, type: T.Type, completionHandler: @escaping (_ error: Error?, _ myObject: T?) -> ()) {
    URLSession.shared.dataTask(with: url) { (data, response, error) in
        // handle error
        do {
            let myNewObject = try JSONDecoder().decode(T.self, from: data!)
            completionHandler(nil, myNewObject)
        } catch let error {
            completionHandler(error, nil)
            return
        }
    }.resume()
}