我使用DispatchGroup尝试对我的客户端运行2个网络请求，并在两个请求都完成后返回结果。
我遇到一个问题，就是有时DispatchGroup中一个请求的完成处理程序被调用两次，而另一个请求根本没有被调用。
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，还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，但是有时这些请求之一会调用其自身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原因，如果我短暂离开应用程序会出现这种情况。我的访问令牌的寿命为2分钟。
如果请求收到401响应，我的网络客户端中将有以下方法，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。
if response.statusIs401() {
self?.refreshHandler { success in
guard success else { completion(.failure(TokenError.refused)); return }
self?.request(resource, completion)
}
return
}
我怀疑更新对我的调度组返回的请求执行了某些操作后，再次调用了该方法。
是否可以这种方式链接请求？
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
}
}
答案 0 :(得分：0)
听起来，您需要在网络客户端中执行以下操作：
ID: 1
Address: ****
Encoding: UTF-8
Http-Method: POST
Content-Type: multipart/related; type="text/xml"; boundary="uuid:5210b5e9-ee88-4b88-9330-f95ee62bb28e"; start="<root.message@cxf.apache.org>"; start-info="text/xml"
Headers: {Accept=[*/*], SOAPAction=["****"]}
Payload: --uuid:5210b5e9-ee88-4b88-9330-f95ee62bb28e
Content-Type: text/xml; charset=UTF-8
Content-Transfer-Encoding: binary
Content-ID: <root.message@cxf.apache.org>
<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
<soap:Header>
</soap:Header>
<soap:Body>
<metodo>
<documento>
<contenido href="8849d331-555b-4ab4-b90d-6ff0996cadcc@apache.org"/>
<hash>0p9oDCPlhlxNemvtT5tj6e46SHdPWLOxTi1sLJBeCz4=</hash>
</documento>
</metodo>
</soap:Body>
</soap:Envelope>
--uuid:5210b5e9-ee88-4b88-9330-f95ee62bb28e
Content-Type: application/pdf
Content-Transfer-Encoding: binary
Content-ID: <8849d331-555b-4ab4-b90d-6ff0996cadcc@apache.org>
%PDF-1.4
%????
2 0 obj
<</Length 76/Filter/FlateDecode>>stream
x?+?r
?26S?00I?2P?5?1??
?B?4<Rsr???rR
?JS?
@?]C????
endstream
endobj
4 0 obj
<</Parent 3 0 R/Contents 2 0 R/Type/Page/Resources<</ProcSet [/PDF /Text /ImageB /ImageC /ImageI]/Font<</F1 1 0 R>>>>/MediaBox[0 0 595 842]>>
endobj
1 0 obj
<</BaseFont/Helvetica/Type/Font/Encoding/WinAnsiEncoding/Subtype/Type1>>
endobj
3 0 obj
<</ITXT(2.1.7)/Type/Pages/Count 1/Kids[4 0 R]>>
endobj
5 0 obj
<</Type/Catalog/Pages 3 0 R>>
endobj
6 0 obj
<</Producer(iText 2.1.7 by 1T3XT)/ModDate(D:20150327140035+01'00')/CreationDate(D:20150327140035+01'00')>>
endobj
xref
0 7
0000000000 65535 f
0000000314 00000 n
0000000015 00000 n
0000000402 00000 n
0000000157 00000 n
0000000465 00000 n
0000000510 00000 n
trailer
<</Root 5 0 R/ID [<5d256b5d87f178862dd33943e65718e8><ecd829bf4e1d355aef68138d0de19d76>]/Info 6 0 R/Size 7>>
startxref
632
%%EOF
--uuid:5210b5e9-ee88-4b88-9330-f95ee62bb28e--
这将进行调用，检查响应代码，刷新需要的令牌，如果调用成功，则调用方法，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这种方式，应该不会太难