Agfdhyk

We are currently making an iOS app and with firebase as its database. Please find below our code.

static func getTilesPerRow () -> Int{



    let user = Auth.auth().currentUser

    guard let uid = user?.uid else {

        return -2

    }

    var ref: DatabaseReference!

    ref = Database.database().reference()

    let userRef = ref.child("user").child(uid)



    var num = -1



    let queue = DispatchQueue(label: "observer")



    userRef.child("tilesPerRow").observe(DataEventType.value, with: { (snapshot) in

        // Get user value

        print("now inside the observe thing------------------")

        let value = snapshot.value as? NSDictionary

        num = snapshot.value as? Int ?? 0

        print("just updated the number to ", num)

        print("the snapshot is ", snapshot)

        print("the value is ", value)

        print("the real value is", snapshot.value)

        print("just making sure, the number that was set is ", num)



    }) { (error) in

        print("there was an error!!!!!!!!!!!!!!!!!")

        print(error.localizedDescription)

    }



    print("about to return from the function ", num)

    return num

}

Currently while running this code, we get the following output.

about to return from the function  -1

now inside the observe thing------------------

just updated the number to  5

the snapshot is  Snap (tilesPerRow) 5

the value is  nil

the real value is Optional(5)

just making sure, the number that was set is  5

Our expected output is:

now inside the observe thing------------------

just updated the number to  5

the snapshot is  Snap (tilesPerRow) 5

the value is  nil

the real value is Optional(5)

just making sure, the number that was set is  5

about to return from the function  5

The problem here is that we are trying to grab the value of what the query has found, but because .observe() is asynchronous, the function finishes before .observe() updates the value of num. How do we return the correct value?

You don't.

To get the asynchronous operation result you use blocks.

static func getTilesPerRow (@escaping completion: (Int?)->Void ) {



    let user = Auth.auth().currentUser

    guard let uid = user?.uid else {

        completion(nil)

    }

    var ref: DatabaseReference!

    ref = Database.database().reference()

    let userRef = ref.child("user").child(uid)



    userRef.child("tilesPerRow").observeSingleEvent(DataEventType.value, with: { (snapshot) in

        // Get user value

        print("now inside the observe thing------------------")

        let value = snapshot.value as? NSDictionary

        let num = snapshot.value as? Int ?? 0

        completion(num)



    }) { (error) in

        print("there was an error!!!!!!!!!!!!!!!!!")

        print(error.localizedDescription)

        completion(nil)

    }

}

When the results are ready you will get notified through the block. Upon success you get the actual num you are looking for or nil upon any error occurred.

Even you can distinguish that what sort of error occurred by adding extra parameter on your parameter list in completion block.

You also could use protocol, but thats require more knowledge like, in which class this code reside, who is the caller this sort of things. Set the protocol target to the caller, and upon completion called method will fire different protocol method based on the error or successful case occurred.

Happy coding.