slimboy slimboy - 2 months ago 25
iOS Question

wait for two asynchronous completion functions to finish, before executing next line code

I have two functions:

func Females_NonChat()
and
func males_NonChat()

I want to wait for both of them to finish before executing the print statement in viewdidload. Do I need another completion handler to accomplish that?

Those functions used are firebase completion handlers for requesting information from the online database...

override func viewDidLoad() {
super.viewDidLoad()
func Females_NonChat()
func males_NonChat()

print("finished executing both asynchronous functions")
}

func Females_NonChat(){
Anon_Ref.child("Chatting").child("female").observeSingleEventOfType(.Value, withBlock: {(snapshot) in
if let FemInChatting = snapshot.value as? [String : String] {
print("executing")
}
})
}

func males_NonChat(){
Anon_Ref.child("Chatting").child("male").observeSingleEventOfType(.Value, withBlock: {(snapshot) in
print("executing")
})
}

Rob Rob
Answer

Generally you'd use a dispatch group, enter the group before each asynchronous method, leave the group upon completion of each asynchronous method, and then set up a group notification when all "enter" calls are matched by corresponding "leave" calls:

override func viewDidLoad() {
    super.viewDidLoad()

    let group = dispatch_group_create()

    dispatch_group_enter(group)
    Females_NonChat() {
        dispatch_group_leave(group)
    }

    dispatch_group_enter(group)
    males_NonChat() {
        dispatch_group_leave(group)
    }

    dispatch_group_notify(group, dispatch_get_main_queue()) { 
        print("finished executing both asynchronous functions")
    }
}

func Females_NonChat(completionHandler: () -> ()) {
    Anon_Ref.child("Chatting").child("female").observeSingleEventOfType(.Value) { snapshot in
        if let FemInChatting = snapshot.value as? [String : String] {
            print("executing")
        }
        completionHandler()
    }
}

func males_NonChat(completionHandler: () -> ()) {
    Anon_Ref.child("Chatting").child("male").observeSingleEventOfType(.Value) { snapshot in
        print("executing")
        completionHandler()
    }
}
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