multithreading - Facebook API Threading in Swift -

one think executing fbsdkgraphrequestconnection , processing result straightforward task, seems threading causing problems.

i trying load facebook friends list , display in table. pretty basic. retrieving list no problem, table tries created before list has been retrieved. threading issue--the table create starts before list retrieval finishes. i've tried several different dispatchgroup suggestions, seems fbsdkgraphrequestconnection runs independently dispatchgroup (and seems running on main thread, too).

i have gotten several other sample programs work properly, none use facebook api, leads me believe that block queued independently. i'm looking suggestions how block tableview(_:cellforrowat:) until after fbsdkgraphrequstconnection.connection finished.

for reference, here's code retrieve friend's list (again, part working fine).

        let params = ["fields": "id, first_name, last_name, name, email, picture"]         let graphrequest = fbsdkgraphrequest(graphpath: "/me/friends", parameters: params)         let connection = fbsdkgraphrequestconnection()         connection.add(graphrequest, completionhandler: { (connection, result, error) in             if error == nil {                 print("request friends result : \(result!)")             } else {                 print("error getting friends \(string(describing: error))");             }         })         connection.start() 

edit: requested, here's 1 of more promising attempts @ getting work. comes https://www.raywenderlich.com/148515/grand-central-dispatch-tutorial-swift-3-part-2. in exercise, 3 pictures downloaded internet, alert box indicating pictures have finished downloading appears before they've finished downloading. first snippet handles request download images internet , displays alert:

// internet button let internetaction = uialertaction(title: "le internet", style: .default) {   _ in   self.downloadimageassets() } alert.addaction(internetaction) 

the images downloaded using:

func downloadimageassets() {     photomanager.sharedmanager.downloadphotoswithcompletion() {       error in       let message = error?.localizeddescription ?? "the images have finished downloading"       let alert = uialertcontroller(title: "download complete", message: message, preferredstyle: .alert)       alert.addaction(uialertaction(title: "ok", style: .cancel, handler: nil))       self.present(alert, animated: true, completion: nil)     } } 

the original downloadphotoswithcompletion(_:) returns immediately, 2 different fixes given. first (and more explicit more cumbersome), both work equivalently:

func downloadphotoswithcompletion(_ completion: batchphotodownloadingcompletionclosure?) {         dispatchqueue.global(qos: .userinitiated).async {         var storederror: nserror?         let downloadgroup = dispatchgroup()         address in [overlyattachedgirlfriendurlstring, successkidurlstring, lotsoffacesurlstring] {             let url = url(string: address)             downloadgroup.enter()             let photo = downloadphoto(url: url!) {                 _, error in                 if error != nil {                     storederror = error                 }                 downloadgroup.leave()             }             photomanager.sharedmanager.addphoto(photo)         }         downloadgroup.wait()         dispatchqueue.main.async {             completion?(storederror)         }     } 

i, then, tried replacing loop facebook call:

    dispatchqueue.global(qos: .userinitiated).async {         let downloadgroup = dispatchgroup()          let params = ["fields": "id, first_name, last_name, name, email, picture"]         let graphrequest = fbsdkgraphrequest(graphpath: "/me/friends", parameters: params)         let connection = fbsdkgraphrequestconnection()         connection.add(graphrequest, completionhandler: { (connection, result, error) in             if error == nil {                 print("request friends result : \(result!)")             } else {                 print("error getting friends \(string(describing: error))");             }             downloadgroup.leave()         })         connection.start()         downloadgroup.wait()         dispatchqueue.main.async {             completion?(nil)         }     } 

the behavior same--the table starts being created before facebook call completes.