Accessing a completion variable outside the function

Question

Created Nov ’23

Replies 2

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Participants 2

I am retrieving a value from a remote json file through task in a function with a completion code (as recommended practice) where I retrieve a date. I then need to use that date in subsequent processing. In this case, return the date and continue my processing. I can work with the date with in the function (see below) but I can't get the value outside the function. Any help would be appreciated.

case .remote:
    var fetchDate: Date?
    fetchRemoteArticlesDate { date in
      fetchDate = date
       // finds the correct date
       print("* fetchDate1: \(String(describing: fetchDate))" )
     }
     // How can I receive the date from fetchRemoteArticlesData so I can return it?
     print("* fetchDate2: \(fetchDate ?? DateInfo.zeroDate)")
     return fetchDate ?? DateInfo.zeroDate

    class func fetchRemoteArticlesDate(completion: @escaping (Date) -> Void) {
        let urlString = AppValues.articlesLocation.remote
        let url = URL(string: urlString)!
        
        let session = URLSession.shared
        let task = session.dataTask(with: url) { (data, response, error) in
            if let error = error {
                LogEvent.print(module: "Articles.fetchArticles", message: "Error saving articles.json: \(error)")
                DispatchQueue.main.sync {
                    completion(DateInfo.zeroDate)
                }
                return
            }
            guard let myData = data else {
                LogEvent.print(module: "Articles.fetchArticles", message: "no JSON data received")
                DispatchQueue.main.async {
                    completion(DateInfo.zeroDate)
                }
                return
            }
            let date = decodeArticlesDateV2(myData)
            LogEvent.print(module: "Articles.articlesDate", message: "\(UserSettings.init().articlesLocation.description) date: \(date)")
            completion(date)
        }
        task.resume()
    }

Boost

Answer 1

OpExNetworks OP

Nov ’23

I'll add using a variable outside the functions does not work. They do not update. I'm guessing that either the value can't escape the context of the function or somehow out of the task has to move up to the main thread in some controlled sequence to ensure it updates. I've tried playing with Dispatch Queues but I am either not doing them right or they don't work either.

0

Answer 2

Claude31 OP

Nov ’23

If I understand your code correctly:

case .remote:
    var fetchDate: Date?
    fetchRemoteArticlesDate { date in
      fetchDate = date
       // finds the correct date
       print("* fetchDate1: \(String(describing: fetchDate))" )
     }
     // How can I receive the date from fetchRemoteArticlesData so I can return it?
     print("* fetchDate2: \(fetchDate ?? DateInfo.zeroDate)")
     return fetchDate ?? DateInfo.zeroDate

What do you get in print ? zeroDate ?

If so it is because func returns before fetchRemoteArticlesDate completion is executed.

To confirm, you could try to wait for a moment:

     // How can I receive the date from fetchRemoteArticlesData so I can return it?
     sleep(1). // Just for testing
     print("* fetchDate2: \(fetchDate ?? DateInfo.zeroDate)")
     return fetchDate ?? DateInfo.zeroDate

In such a case, I would use wait async is a pattern.

0