xcode - How to wait for a background function to finish before calling another one in swift? -
i try explain briefly situation is. building quiz app , wanted work using internet, work while when user disconnected. older code using made synchronous queries, taking more time expected. decided reformulate it. situation projected following:
when user selects subject app synchronously 1 question each subsubject in order ready user click , faster.
after getting first question, app 4 (or how needed complete 5) each of subsubjects asynchronously, while user occupied answering first question presented him.
finally, app save objects in local datastore, user can answer 5 questions each subsubject when not connected.
here code:
func getquestionsremotelyandsave (subsubject:string?, subject:string?, arrayofsubsubjects:[string]?) { self.getfromuserdefaults() if reachability.isconnectedtonetwork() == true { if self.needstogetquestions == true { let user = pfuser.currentuser() var query = pfquery(classname: "questions") query.wherekey("answeredby", equalto: user) query.wherekey("grade", equalto: user["grade"]) if subsubject != nil && subject == nil { query.wherekey("subsubject", equalto: subsubject) query.limit = 2 let array = query.findobjects() item in array { let object = item pfobject var questiontopin = pfobject(classname: "questions") questiontopin["question"] = object["question"] string questiontopin["rightanswer"] = object ["rightanswer"] string questiontopin["wronganswer1"] = object ["wronganswer1"] string questiontopin["wronganswer2"] = object ["wronganswer2"] string questiontopin["wronganswer3"] = object ["wronganswer3"] string questiontopin["grade"] = object["grade"] string questiontopin["subject"] = object ["subject"] string questiontopin["subsubject"] = object ["subsubject"] string questiontopin["feedback"] = object ["feedback"] as? string questiontopin["shortfeedback1"] = object ["shortfeedback1"] as? string questiontopin["shortfeedback2"] = object ["shortfeedback2"] as? string questiontopin["shortfeedback3"] = object ["shortfeedback3"] as? string questiontopin.pin() } query.limit = 3 query.findobjectsinbackgroundwithblock({ (objects:[anyobject]!, error:nserror!) -> void in if error == nil { let questions = objects [pfobject] var questionstopin = [pfobject]() object in questions { var questiontopin = pfobject(classname: "questions") questiontopin["question"] = object["question"] string questiontopin["rightanswer"] = object ["rightanswer"] string questiontopin["wronganswer1"] = object ["wronganswer1"] string questiontopin["wronganswer2"] = object ["wronganswer2"] string questiontopin["wronganswer3"] = object ["wronganswer3"] string questiontopin["grade"] = object["grade"] string questiontopin["subject"] = object ["subject"] string questiontopin["subsubject"] = object ["subsubject"] string questiontopin["feedback"] = object ["feedback"] as? string questiontopin["shortfeedback1"] = object ["shortfeedback1"] as? string questiontopin["shortfeedback2"] = object ["shortfeedback2"] as? string questiontopin["shortfeedback3"] = object ["shortfeedback3"] as? string questiontopin.pininbackground() } } }) } if subsubject == nil && subject != nil { var firsttime = true var semaphore = dispatch_semaphore_create(0) query.limit = 1 item in arrayofsubsubjects! { if item != "todas matérias" { var query3 = pfquery(classname: "questions") query3.fromlocaldatastore() query3.wherekey("subsubject", equalto: item) let count = query3.countobjects() if count == 0 { query.wherekey("subsubject", equalto: item) let array:nsarray = query.findobjects() item in array { let object = item pfobject var questiontopin = pfobject(classname: "questions") questiontopin["question"] = object["question"] string questiontopin["rightanswer"] = object ["rightanswer"] string questiontopin["wronganswer1"] = object ["wronganswer1"] string questiontopin["wronganswer2"] = object ["wronganswer2"] string questiontopin["wronganswer3"] = object ["wronganswer3"] string questiontopin["grade"] = object["grade"] string questiontopin["subject"] = object ["subject"] string questiontopin["subsubject"] = object ["subsubject"] string questiontopin["feedback"] = object ["feedback"] as? string questiontopin["shortfeedback1"] = object ["shortfeedback1"] as? string questiontopin["shortfeedback2"] = object ["shortfeedback2"] as? string questiontopin["shortfeedback3"] = object ["shortfeedback3"] as? string questiontopin.pin() } } if count > 0 { var limit = 5 - count if limit < 0 { limit = 0 } query.limit = limit if firsttime == false { dispatch_semaphore_wait(semaphore, dispatch_time_forever) } query.findobjectsinbackgroundwithblock({ (objects:[anyobject]!, error:nserror?) -> void in if error == nil { let questions = objects [pfobject] object in questions { var questiontopin = pfobject(classname: "questions") questiontopin["question"] = object["question"] string questiontopin["rightanswer"] = object ["rightanswer"] string questiontopin["wronganswer1"] = object ["wronganswer1"] string questiontopin["wronganswer2"] = object ["wronganswer2"] string questiontopin["wronganswer3"] = object ["wronganswer3"] string questiontopin["grade"] = object["grade"] string questiontopin["subject"] = object ["subject"] string questiontopin["subsubject"] = object ["subsubject"] string questiontopin["feedback"] = object ["feedback"] as? string questiontopin["shortfeedback1"] = object ["shortfeedback1"] as? string questiontopin["shortfeedback2"] = object ["shortfeedback2"] as? string questiontopin["shortfeedback3"] = object ["shortfeedback3"] as? string questiontopin.pininbackground() } dispatch_semaphore_signal(semaphore) firsttime = false } }) } } } } } } } the problem i'm facing cant request multiple asynchronous functions parse. thought maybe waiting asynchronous function finish before other 1 starts, wanted happen without user having wait. there way of doing it?
thank you.
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