我正在構建一個網路 API。我是 Combine 的新手，遇到了一些麻煩，我正在嘗試鏈接發布網路請求，在這種情況下，我正在組建一個 URLRequest 發布者并將其分發到另一個發布者，問題是我無法flatMap 在第二個發布者上作業。
首先，我URLRequest使用 Auth 令牌組合：
func asURLRequest(baseURL: String) -> AnyPublisher<URLRequest, NetworkRequestError> {
return Deferred {
Future<URLRequest, NetworkRequestError> { promise in
if var urlComponents = URLComponents(string: baseURL) {
urlComponents.path = "\(urlComponents.path)\(path)"
urlComponents.queryItems = queryItemsFrom(params: queryParams)
if let finalURL = urlComponents.url {
if let user = Auth.auth().currentUser {
print("##### final url -> \(finalURL)")
// Retrieves the Firebase authentication token, possibly refreshing it if it has expired.
user.getIDToken(completion: { (token, error) in
if let fbToken = token {
var request = URLRequest(url: finalURL)
request.httpMethod = method.rawValue
request.httpBody = requestBodyFrom(params: body)
let defaultHeaders: HTTPHeaders = [
HTTPHeaderField.contentType.rawValue: contentType.rawValue,
HTTPHeaderField.acceptType.rawValue: contentType.rawValue,
HTTPHeaderField.authentication.rawValue: fbToken
]
request.allHTTPHeaderFields = defaultHeaders.merging(headers ?? [:], uniquingKeysWith: { (first, _) in first })
print("##### API TOKEN() SUCCESS: \(defaultHeaders)")
promise(.success(request))
}
if let fbError = error {
print("##### API TOKEN() ERROR: \(fbError)")
promise(.failure(NetworkRequestError.decodingError))
}
})
}
} else {
promise(.failure(NetworkRequestError.decodingError))
}
} else {
promise(.failure(NetworkRequestError.decodingError))
}
}
}.eraseToAnyPublisher()
}
然后我試圖發送一個請求（發布者）并回傳另一個發布者，問題是 .flatMap 沒有被呼叫：
struct APIClient {
var baseURL: String!
var networkDispatcher: NetworkDispatcher!
init(baseURL: String,
networkDispatcher: NetworkDispatcher = NetworkDispatcher()) {
self.baseURL = baseURL
self.networkDispatcher = networkDispatcher
}
/// Dispatches a Request and returns a publisher
/// - Parameter request: Request to Dispatch
/// - Returns: A publisher containing decoded data or an error
func dispatch<R: Request>(_ request: R) -> AnyPublisher<R.ReturnType, NetworkRequestError> {
print("##### --------> \(request)")
//typealias RequestPublisher = AnyPublisher<R.ReturnType, NetworkRequestError>
return request.asURLRequest(baseURL: baseURL)
.flatMap { request in
//NOT GETTING CALLED
self.networkDispatcher.dispatch(request: request)
}.eraseToAnyPublisher()
}
未被呼叫的最終發布者如下：
struct NetworkDispatcher {
let urlSession: URLSession!
public init(urlSession: URLSession = .shared) {
self.urlSession = urlSession
}
/// Dispatches an URLRequest and returns a publisher
/// - Parameter request: URLRequest
/// - Returns: A publisher with the provided decoded data or an error
func dispatch<ReturnType: Codable>(request: URLRequest) -> AnyPublisher<ReturnType, NetworkRequestError> {
return urlSession
.dataTaskPublisher(for: request)
// Map on Request response
.tryMap({ data, response in
// If the response is invalid, throw an error
if let response = response as? HTTPURLResponse,
!(200...299).contains(response.statusCode) {
throw httpError(response.statusCode)
}
// Return Response data
return data
})
// Decode data using our ReturnType
.decode(type: ReturnType.self, decoder: JSONDecoder())
// Handle any decoding errors
.mapError { error in
handleError(error)
}
// And finally, expose our publisher
.eraseToAnyPublisher()
}
}
運行代碼：
struct ReadUser: Request {
typealias ReturnType = UserData
var path: String
var method: HTTPMethod = .get
init(_ id: String) {
path = "users/\(id)"
}
}
let apiClient = APIClient(baseURL: BASE_URL)
var cancellables = [AnyCancellable]()
apiClient.dispatch(ReadUser(Auth.auth().currentUser?.uid ?? ""))
.receive(on: DispatchQueue.main)
.sink(
receiveCompletion: { result in
switch result {
case .failure(let error):
// Handle API response errors here (WKNetworkRequestError)
print("##### Error loading data: \(error)")
default: break
}
},
receiveValue: { value in
})
.store(in: &cancellables)
uj5u.com熱心網友回復：
我把你的代碼歸結為僅結合部分。我無法重現您所描述的問題。我將在下面發布該代碼。我建議你開始一次簡化你的代碼，看看是否有幫助。將 Auth 和 Facebook 令牌代碼分解出來似乎是一個不錯的選擇。另一種很好的除錯技術可能是放入更明確的型別宣告，以確保您的閉包正在接受并回傳您期望的內容。（就在前幾天map，當我真正映射到 Optional 時，我認為我正在申請一個陣列）。
這是游樂場：
匯入 UIKit 匯入結合
func asURLRequest(baseURL: String) -> AnyPublisher<URLRequest, Error> {
return Deferred {
Future<URLRequest, Error> { promise in
promise(.success(URLRequest(url: URL(string: "https://www.apple.com")!)))
}
}.eraseToAnyPublisher()
}
struct APIClient {
var networkDispatcher: NetworkDispatcher!
init(networkDispatcher: NetworkDispatcher = NetworkDispatcher()) {
self.networkDispatcher = networkDispatcher
}
func dispatch() -> AnyPublisher<Data, Error> {
return asURLRequest(baseURL: "Boo!")
.flatMap { (request: URLRequest) -> AnyPublisher<Data, Error> in
print("Request Received. \(String(describing: request))")
return self.networkDispatcher.dispatch(request: request)
}.eraseToAnyPublisher()
}
}
func httpError(_ code: Int) -> Error {
return NSError(domain: "Bad Things", code: -1, userInfo: nil)
}
func handleError(_ error: Error) -> Error {
debugPrint(error)
return error
}
struct NetworkDispatcher {
let urlSession: URLSession!
public init(urlSession: URLSession = .shared) {
self.urlSession = urlSession
}
func dispatch(request: URLRequest) -> AnyPublisher<Data, Error> {
return urlSession
.dataTaskPublisher(for: request)
.tryMap({ data, response in
if let response = response as? HTTPURLResponse,
!(200...299).contains(response.statusCode) {
throw httpError(response.statusCode)
}
// Return Response data
return data
})
.mapError { error in
handleError(error)
}
.eraseToAnyPublisher()
}
}
let apiClient = APIClient()
var cancellables = [AnyCancellable]()
apiClient.dispatch()
.print()
.receive(on: DispatchQueue.main)
.sink(
receiveCompletion: { result in
debugPrint(result)
switch result {
case .failure(let error):
// Handle API response errors here (WKNetworkRequestError)
print("##### Error loading data: \(error)")
default: break
}
},
receiveValue: { value in
debugPrint(value)
})
.store(in: &cancellables)
uj5u.com熱心網友回復：
我重構了你的代碼。將違規方法分解為幾個功能。我找不到任何問題。下面是我的重構。您會注意到，我將構建事物的所有代碼分解為它們自己的函式，因此它們可以在不處理效果的情況下輕松測驗（我什至不必模擬效果來測驗邏輯。）
extension Request {
func asURLRequest(baseURL: String) -> AnyPublisher<URLRequest, NetworkRequestError> {
guard let user = Auth.auth().currentUser else {
return Fail(error: NetworkRequestError.missingUser)
.eraseToAnyPublisher()
}
return user.idTokenPublisher()
.catch { error in
Fail(error: NetworkRequestError.badToken(error))
}
.tryMap { token in
makeRequest(
finalURL: try finalURL(baseURL: baseURL),
fbToken: token
)
}
.eraseToAnyPublisher()
}
func finalURL(baseURL: String) throws -> URL {
guard var urlComponents = URLComponents(string: baseURL) else {
throw NetworkRequestError.malformedURLComponents
}
urlComponents.path = "\(urlComponents.path)\(path)"
urlComponents.queryItems = queryItemsFrom(params: queryParams)
guard let result = urlComponents.url else {
throw NetworkRequestError.malformedURLComponents
}
return result
}
func makeRequest(finalURL: URL, fbToken: String) -> URLRequest {
var request = URLRequest(url: finalURL)
request.httpMethod = method.rawValue
request.httpBody = requestBodyFrom(params: body)
let defaultHeaders: HTTPHeaders = [
HTTPHeaderField.contentType.rawValue: contentType.rawValue,
HTTPHeaderField.acceptType.rawValue: contentType.rawValue,
HTTPHeaderField.authentication.rawValue: fbToken
]
request.allHTTPHeaderFields = defaultHeaders.merging(
headers ?? [:],
uniquingKeysWith: { (first, _) in first }
)
return request
}
}
extension User {
func idTokenPublisher() -> AnyPublisher<String, Error> {
Deferred {
Future { promise in
getIDToken(completion: { token, error in
if let token = token {
promise(.success(token))
}
else {
promise(.failure(error ?? UnknownError()))
}
})
}
}
.eraseToAnyPublisher()
}
}
struct UnknownError: Error { }
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