i understand how use dispatch group in simple for-loop. i, however, have more complicated for-loop more asynchronous calls within it. want asynchronous calls complete before executing group completion code. have tried apply principles in answer no avail- can use dispatch group not in loop?. here code, based off of techniques observed in link:
let group = dispatchgroup() ref in self.notifsreflist { group.enter() self.db.fetch(withrecordid: ref.recordid) { notifrecord, notiferr in print("async call") if notiferr == nil { // stuff if let ref = notifrecord?.object(forkey: post) as! ckreference? { group.enter() self.db.fetch(withrecordid: ref.recordid) { postrecord, err in print("async call") if err == nil { // stuff group.leave() } else { print("\(err)") group.leave() } } } if let ref = notifrecord?.object(forkey: user_notif) as! ckreference? { self.db.fetch(withrecordid: ref.recordid) { userrecord, err2 in group.enter() print("async call") if err2 == nil { // stuff group.leave() } else { print("\(err2)") group.leave() } } } if let ref = notifrecord?.object(forkey: library_item) as! ckreference? { self.db.fetch(withrecordid: ref.recordid) { librecord, err3 in group.enter() print("async call") if err3 == nil { // stuff group.leave() } else { print("\(err3)") group.leave() } } } group.leave() } else { print("\(notiferr)") group.leave() } } } group.notify(queue: .main, execute: { // executed after async calls in loop finish print("done async calls") // stuff }) from print statements included, know asynchronous calls incorrect: "done async calls" prints before instances of "async call." in how dispatch group working appreciated. thanks!
the problem 2nd , 3rd inner async calls. calling group.enter() inside completion blocks instead of before async calls.
there's no need many calls leave.
you need move 2 follows:
let group = dispatchgroup() ref in self.notifsreflist { group.enter() self.db.fetch(withrecordid: ref.recordid) { notifrecord, notiferr in print("async call") if notiferr == nil { // stuff if let ref = notifrecord?.object(forkey: post) as! ckreference? { group.enter() self.db.fetch(withrecordid: ref.recordid) { postrecord, err in print("async call") if err == nil { // stuff } else { print("\(err)") } group.leave() } } if let ref = notifrecord?.object(forkey: user_notif) as! ckreference? { group.enter() self.db.fetch(withrecordid: ref.recordid) { userrecord, err2 in print("async call") if err2 == nil { // stuff } else { print("\(err2)") } group.leave() } } if let ref = notifrecord?.object(forkey: library_item) as! ckreference? { group.enter() self.db.fetch(withrecordid: ref.recordid) { librecord, err3 in print("async call") if err3 == nil { // stuff } else { print("\(err3)") } group.leave() } } } else { print("\(notiferr)") } group.leave() } } group.notify(queue: .main, execute: { // executed after async calls in loop finish print("done async calls") // stuff }) 
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