swift - 使用完成处理程序调用函数

Question

我创建了下面的函数，但我不确定如何调用它，它提示说:

Type 'T.Type' cannot conform to 'Decodable' 

我想这样调用它:

let result = getApiData(modelToDecode: MyModel, url: "abc")

这是我试过的:

func getApiData<T : Decodable>(modelToDecode: T.Type, url: String) -> Any? {
    // I get an error below
    fetchDataAndDecode(url: String, modelToDecode: T.Type) { result in
    }

    // temp placeholder
    return nil
}

func fetchDataAndDecode<T : Decodable>(url: String, modelToDecode: T.Type, completionHandler: @escaping (Result<T.Type, NetworkError>) -> Void) {
    guard let url = URL(string: url) else {
        completionHandler(.failure(NetworkError.badURL))
        return
    }

    AF.request(url, method: .get).validate().responseData { response in
        guard let data = response.data else {
            completionHandler(.failure(NetworkError.apiFailed))
            return
        }

        do {
            // Decode the data
            let decodedData = try JSONDecoder().decode(modelToDecode.self, from: data)
            DispatchQueue.main.async {
                completionHandler(.success(decodedData as! T.Type))
            }
        } catch(let error) {
            print("🛑 Error on afRequest(): \(error)")
        }
    }
}

如何在类里面正确调用它？

Answer 1

结果应为 Result<T, NetworkError> .无需添加 modelToDecode到你的方法声明。您可以在异步调用中显式设置结果类型。顺便说一句，如果您无法解码数据，您也应该使用完成处理程序:

enum NetworkError: Error {
    case badURL, apiFailed, corruptedData
}

---

你的方法应该是这样的:

func fetchDataAndDecode<T: Decodable>(url: String, completionHandler: @escaping (Result<T, NetworkError>) -> Void) {
    guard let url = URL(string: url) else {
        completionHandler(.failure(.badURL))
        return
    }

    AF.request(url, method: .get).validate().responseData { response in
        guard let data = response.data else {
            completionHandler(.failure(.apiFailed))
            return
        }

        do {
            let decodedData = try JSONDecoder().decode(T.self, from: data)
            DispatchQueue.main.async {
                completionHandler(.success(decodedData))
            }
        } catch {
            completionHandler(.failure(.corruptedData))
        }
    }
}

---

并且在调用它时你需要显式设置结果类型:

fetchDataAndDecode(url: "yourURL") { (result: Result<WhatEver, NetworkError>) in 
    // switch the result here
}