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Execute Completion Handler in DispatchGroup


Execute Completion Handler in DispatchGroup

By : user2176663
Date : October 14 2020, 02:15 PM
With these it helps First, there's a few things you should note about your existing code.
code :
pingQueue = DispatchQueue(label: "PingQueue", qos: .background)

let client = SimplePingClient()
client.pingHostname(
    hostname: self.Servers[indexPath.row].Address, // This is jank, but I'm ignoring it for now
    andResultCallback: { _latency in
        pingQueue.sync {
            print("Do some stuff on pingQueue")

            DispatchQueue.main.sync { // enter main queue for UI updates
                cell.lblLatency.text = (_latency as? String).map { $0 + " ms" } ?? "Timeout"
            }
        }
    }
)


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Re-execute while loop after completion handler has been returned

Re-execute while loop after completion handler has been returned


By : einervonvielen
Date : March 29 2020, 07:55 AM
Hope this helps You shouldn't do this with a loop. That's the whole point of Alamofire, so you don't have to deal with threads and loops. You're working with high level instructions: callbacks.
It's actually very easy to solve your problem:
code :
var empty = true
override func viewDidLoad() {
 self.tryGettingDataFromServer()
}

func tryGettingDataFromServer(){
 str = iFunctions.generateRandomStringWithLengthOf(4) as String
 iFunctions.getServerData(str){(msg) in
    if (msg > 0){
        self.empty = false
        print("not empty")
    }
    else{
        // The closure keeps a reference to self and calls
        // the tryGettingDataFromServer again if "empty"
        // It will happen infinitely until "not empty"
        self.tryGettingDataFromServer()
    }
    self.count = msg!
    print(self.count)
  }

}
Execute completion handler when condition is met

Execute completion handler when condition is met


By : user5519487
Date : March 29 2020, 07:55 AM
will be helpful for those in need You have to add a completion handler to the function which needs to be completed before the other like this:
code :
func completedLogin(sender: LogInScreen, completionHandler :(evaluatedSuccessfully: Bool) -> ()){


self.loginCompleted = true
completionHandler(evaluatedSuccessfully: true)
}
completedLogin(sender: <your sender>){ success in

If success{
//do something
}

else{
//report an error
}
}
-- swift: async + JSON + completion + DispatchGroup

-- swift: async + JSON + completion + DispatchGroup


By : Mastra Yasa
Date : March 29 2020, 07:55 AM
Hope that helps Because fetchJSON returns immediately, before the JSON is downloaded. The effect is that the DispatchGroup is entereed and left right away, without waiting for the JSON:
code :
group.enter()
self.fetchJSON() // returns immediately
group.leave()    // the JSON has yet to be downloaded
override func viewDidLoad() {
    group.enter()
    self.fetchJSON { 
        group.notify(queue: .main)  {
            print("JSON call finished")
        }
        group.leave()
    }
}

// Change the data type of the completion handler accordingly
func fetchJSON(completionHandler: @escaping (Data?) -> Void) {
    // ...
    networkService.downloadJSONasync(searchItem: AppConstants.appString.startString) { fetchedData in
        defer { completionHandler(fetchedData) }
        // ...
    }
)
Swift inferring a completion handler closure to be the default @nonescaping instead of @escaping when completion handler

Swift inferring a completion handler closure to be the default @nonescaping instead of @escaping when completion handler


By : user2495254
Date : March 29 2020, 07:55 AM
it fixes the issue The problem has nothing to do with the closure, or static, or private. It has to do with the type parameter. You cannot call this method:
code :
private static func getAndCacheAPIData <CodableClass: Any & Codable>(type:CodableClass.Type, completionHandler: @escaping (String?)->Void)
private static func getAndCacheAPIData(type: Codable.Type, completionHandler: @escaping (String?)->Void)
 AppNetwork.getAndCacheAPIData(type: Int.self) {(firstErrorString) in ... }
let completion: (String?) -> Void = {(firstErrorString) in ... }

switch ... {
    case ...:
        AppNetwork.getAndCacheAPIData(type: Int.self, completion: completion)
    case ...:
        AppNetwork.getAndCacheAPIData(type: String.self, completion: completion)
    ...
AppNetwork.getAndCacheAPIData(type: Codable.self) {...}
private static func handleAPI<CodableClass: Codable>(type: CodableClass.Type) {
    getAndCacheAPIData(type: type.self) { _ in ... the completion handler ..}
}


switch ... {
    case ...:
        AppNetwork.handleAPI(type: Int.self)
    case ...:
        AppNetwork.handleAPI(type: String.self)
    ...
Parallel URLSession requests w/ DispatchGroup call completion handler twice on 1 request

Parallel URLSession requests w/ DispatchGroup call completion handler twice on 1 request


By : user3442389
Date : March 29 2020, 07:55 AM
seems to work fine Sounds like you would need to something like the following in your networking client:
code :
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)
  }
}
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