使用DispatchGroup
我正在尝试对我的客户端运行2个网络请求,当两个请求都完成时返回结果。
我有一个问题,有时DispatchGroup
请求中的一个的完成处理程序被调用两次,而另一个请求根本不被调用。
一个例子是-
func fetchProfileWithRelatedArticle(onSuccess: @escaping (User, [RelatedArticle]) -> Void, onError: @escaping (Error) -> Void) {
let dispatchGroup = DispatchGroup()
var user: User?
var articles: [RelatedArticle] = []
var errors: [Error] = []
dispatchGroup.enter()
fetchProfileForUser(onSuccess: {
user = $0
print("fetchProfile:",$0)
print("123")
dispatchGroup.leave()
}, onError: { error in
errors.append(error)
dispatchGroup.leave()
})
dispatchGroup.enter()
getArticlesForUser(onSuccess: {
articles = $0
print("getArticlesForUser:",$0)
print("456")
dispatchGroup.leave()
}, onError: { error in
errors.append(error)
dispatchGroup.leave()
})
dispatchGroup.notify(queue: .main) {
guard let user = user, errors.isEmpty else { return }
onSuccess(user, articles)
}
}
我在这里获取用户个人资料,并获取他们撰写的文章列表。这些通过完成处理程序返回并显示在其他位置。
在大多数情况下,此方法有效,但是有时其中一个请求会调用其自己的完成处理程序两次,而另一个请求则不会。
我怀疑这可能是我的访问令牌到期的时间,因为如果我短暂离开应用程序,访问令牌将到期。我的访问令牌的寿命为2分钟。
[如果请求收到401
响应,我的网络客户端中就有以下方法,该方法请求一个新令牌,然后再次调用该调用。我相信这可能无法按照我的意愿进行。
我怀疑更新对我的调度组返回的请求进行了某些处理后,再次调用了该方法。
是否可以这种方式链接请求?
if response.statusIs401() {
self?.refreshHandler { success in
guard success else { completion(.failure(TokenError.refused)); return }
self?.request(resource, completion)
}
return
}
struct NoContent: Codable { }
typealias RefreshHandler = (@escaping (Bool) -> Void) -> ()
typealias TokenGetter = () -> [String: String]
protocol ClientType: class {
associatedtype Route: RouterType
func request<T: Codable>(_ resource: Route, _ completion: @escaping (Result<T>)-> Void)
}
class Client<Route: RouterType>: ClientType {
enum APIError: Error {
case unknown, badResponse, jsonDecoder, other
}
enum TokenError: String, Error {
case expired = "Access Token Expired"
case refused = "Refresh Token Failed"
}
private(set) var session: SessionType
private(set) var tokenGetter: TokenGetter
private(set) var refreshHandler: RefreshHandler
private lazy var decoder: JSONDecoder = {
let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .iso8601withFractionalSeconds
return decoder
}()
init(session: SessionType, tokenGetter: @escaping TokenGetter, refreshHandler: @escaping RefreshHandler) {
self.session = session
self.tokenGetter = tokenGetter
self.refreshHandler = refreshHandler
}
func request<T: Codable>(_ resource: Route, _ completion: @escaping (Result<T>)-> Void) {
let request = URLRequest(
resource: resource,
headers: tokenGetter()
)
URLSession.shared.dataTask(with: request) { [weak self] data, response, error in
guard error == nil else { completion(.failure(APIError.unknown)); return }
guard let response = response as? HTTPURLResponse else { completion(.failure(APIError.badResponse)); return }
if response.statusIs401() {
self?.refreshHandler { success in
guard success else { completion(.failure(TokenError.refused)); return }
self?.request(resource, completion)
}
return
}
if response.statusIsSuccess() {
guard let self = self, let data = self.deserializeNoContentResponse(data: data) else { completion(.failure(APIError.badResponse)); return }
do {
let value = try self.decoder.decode(T.self, from: data)
DispatchQueue.main.async {
completion(.success(value))
}
} catch let error {
print(error)
}
return
}
completion(.failure(APIError.other))
}.resume()
}
// some calls return a 200/201 with no data
private func deserializeNoContentResponse(data: Data?) -> Data? {
if data?.count == 0 {
return "{ }".data(using: .utf8)
}
return data
}
}
听起来您在网络客户端中需要以下内容:
func makeTheRequest(_ completion: CompletionHandler) {
URLSession.shared.dataTask(with: someURL) { data, response, error in
guard let httpResponse = response as? HTTPURLResponse else {
return
}
if httpResponse.statusCode == 401 {
self.refreshToken { success in
if success { self.makeTheRequest(completion) }
}
}
// handle response
completion(whateverDataYouNeedToPass)
}
}
这将进行调用,检查响应代码,需要刷新令牌,如果调用成功,它将调用该方法,该方法应使用首先传递给的完成处理程序再次做出响应,而无需先调用它。因此,只有在第二次调用API之后,才会调用完成处理程序。
当然,为您自己的代码采用它,应该不太难做