[英]Contextual closure type … expects 2 arguments, but 3 were used in closure body
[英]Contextual closure type '(Data?, URLResponse?, Error?) -> Void' expects 3 arguments, but 1 was used in closure body
我正在關注本教程,但收到此錯誤:
上下文閉包類型 '(Data?, URLResponse?, Error?) -> Void' 需要 3 arguments,但閉包主體中使用了 1
在行: urlSession.dataTask(with: url) { (result) in
private func fetchResources<T: Decodable>(url: URL, completion: @escaping (Result<T, APIServiceError>) -> Void) {
guard var urlComponents = URLComponents(url: url, resolvingAgainstBaseURL: true) else {
completion(.failure(.invalidEndpoint))
return
}
let queryItems = [URLQueryItem(name: "api_key", value: apiKey)]
urlComponents.queryItems = queryItems
guard let url = urlComponents.url else {
completion(.failure(.invalidEndpoint))
return
}
urlSession.dataTask(with: url) { (result) in
switch result {
case .success(let (response, data)):
guard let statusCode = (response as? HTTPURLResponse)?.statusCode, 200..<299 ~= statusCode else {
completion(.failure(.invalidResponse))
return
}
do {
let values = try self.jsonDecoder.decode(T.self, from: data)
completion(.success(values))
} catch {
completion(.failure(.decodeError))
}
case .failure(let error):
completion(.failure(.apiError))
}
}.resume()
}
這個dataTask
的閉包需要三個參數,一個Data?
,一個URLResponse?
,和一個Error?
. 你的代碼寫得好像這個閉包有一個參數,一個Result
。 看起來您認為它是Result<(Data, URLResponse), Error>
,但事實並非如此。 這個Result
枚舉是我們在自己的代碼中使用的枚舉,但它不被URLSession
使用。
因此,將dataTask
更改為使用具有三個參數的閉包:
private func fetchResources<T: Decodable>(url: URL, completion: @escaping (Result<T, APIServiceError>) -> Void) {
guard var urlComponents = URLComponents(url: url, resolvingAgainstBaseURL: true) else {
completion(.failure(.invalidEndpoint))
return
}
urlComponents.queryItems = [URLQueryItem(name: "api_key", value: apiKey)]
guard let url = urlComponents.url else {
completion(.failure(.invalidEndpoint))
return
}
urlSession.dataTask(with: url) { data, response, error in
guard error == nil else {
completion(.failure(.apiError))
return
}
guard
let data = data,
let response = response as? HTTPURLResponse,
200...299 ~= response.statusCode
else {
completion(.failure(.invalidResponse))
return
}
do {
let values = try self.jsonDecoder.decode(T.self, from: data)
completion(.success(values))
} catch {
completion(.failure(.decodeError))
}
}.resume()
}
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