Bdtjtk

I have two functions that successfully retrieve integers from Firebase. I'd like a third function that does some simple subtraction from the integers gathered in the first two functions.

However, I'm very new to this, so can't get it to work correctly.

The output of the two functions that gather data from Firebase are:

let pointsRedeemedAsInt:Int = Int(Points_Redeem)!

and

let sumOfPointsCompleted = self.challengeList.reduce(0) {$0 + $1.Points}

What I'd like is a third function that looks like this:

let pointsBalance = sumOfPointsCompleted - pointsRedeemedAsInt

However, the third function doesn't recognise sumOfPointsCompleted, nor pointsRedeemedAsInt.

// First Function:

 func loadPointsRedeemed() {





    databaseReference = Database.database().reference()



    let userID = Auth.auth().currentUser?.uid



    databaseReference.child("Users").child(userID!).observe(DataEventType.value, with: { (snapshot) in



        let value = snapshot.value as? NSDictionary



        // let Points_Earn = value?["Points_Earned"] as? String ?? ""

        let Points_Redeem = value?["Points_Redeemed"] as? String ?? ""





        // self.Points_Earned.text = Points_Earn

        self.Points_Redeemed.text = Points_Redeem



        let pointsRedeemedAsInt:Int = Int(Points_Redeem)!



        // Do any additional setup after loading the view.

    }



)}

//Second Function:

func LoadPointsCompleted() {



    self.challengeList.removeAll()



    databaseReference = Database.database().reference()



    let userID = Auth.auth().currentUser?.uid



    let refChallenges = Database.database().reference(withPath: "Challenges").child(userID!).queryOrdered(byChild: "Status").queryEqual(toValue: "Complete")



    refChallenges.observeSingleEvent(of: .value, with: { (snapshot) in



        //if the reference have some values

        if snapshot.childrenCount > 0 {



            //clearing the list

            self.challengeList.removeAll()



            //iterating through all the values

            for Challenges in snapshot.children.allObjects as! [DataSnapshot] {

                //getting values

                let challengeObject = Challenges.value as? [String: AnyObject]

                let Points = challengeObject?["Points"] as! Int



                //creating challenge object with model and fetched values

                let challenge = pointsModel(Points: (Points as Int?)!)



                //appending it to list

                self.challengeList.append(challenge)



                let sumOfPointsCompleted = self.challengeList.reduce(0) {$0 + $1.Points}



                let sumOfPointsCompletedString = String(sumOfPointsCompleted)

                self.Calc_Earned.text = sumOfPointsCompletedString

            }   

        }

    }   

    )}

// Third Function (which does not work):

 func BalanceOfPoints(){



    let balance = sum - pointsRedeemedAsInt



}

The error is:

Use of unresolved identifiers sum and pointsRedeemedAsInt

Furthermore, how do I ensure that everything is executed in the right order? ie, the loadPointsCompleted function must run (and complete) first, followed by the loadPointsRedeemed function, and finally the BalanceOfPoints function.

Actually, the problem is that you are not considering that retrieving data from remote sources is asynchronous.
This means that you have to wait for data to be retrieved before calling the other functions.

To achieve this result, you should use swift closure (callback in other languages) with completion handler. Check this documentation.

Change your functions this way:

First Function

func loadPointsRedeemed(completion: @escaping (_:Int)->()){



databaseReference = Database.database().reference()



let userID = Auth.auth().currentUser?.uid



databaseReference.child("Users").child(userID!).observe(DataEventType.value, with: { (snapshot) in



    let value = snapshot.value as? NSDictionary



    // let Points_Earn = value?["Points_Earned"] as? String ?? ""

    let Points_Redeem = value?["Points_Redeemed"] as? String ?? ""





    // self.Points_Earned.text = Points_Earn

    self.Points_Redeemed.text = Points_Redeem



    let pointsRedeemedAsInt:Int = Int(Points_Redeem)!



    // Do any additional setup after loading the view.



    //Call your return back function called "completion"

    completion(pointsRedeemedAsInt)



}



)}

Second Function

func loadPointsCompleted(completion: @escaping (_:Int)->()){



self.challengeList.removeAll()



databaseReference = Database.database().reference()



let userID = Auth.auth().currentUser?.uid



let refChallenges = Database.database().reference(withPath: "Challenges").child(userID!).queryOrdered(byChild: "Status").queryEqual(toValue: "Complete")



refChallenges.observeSingleEvent(of: .value, with: { (snapshot) in



    //if the reference have some values

    if snapshot.childrenCount > 0 {



        //clearing the list

        self.challengeList.removeAll()



        //iterating through all the values

        for Challenges in snapshot.children.allObjects as! [DataSnapshot] {

            //getting values

            let challengeObject = Challenges.value as? [String: AnyObject]

            let Points = challengeObject?["Points"] as! Int



            //creating challenge object with model and fetched values

            let challenge = pointsModel(Points: (Points as Int?)!)



            //appending it to list

            self.challengeList.append(challenge)



        }   



        let sumOfPointsCompleted = self.challengeList.reduce(0) {$0 + $1.Points}



        let sumOfPointsCompletedString = String(sumOfPointsCompleted)

        self.Calc_Earned.text = sumOfPointsCompletedString



        completion(sumOfPointsCompleted)



    }

}   

)}

Third Function

 func balanceOfPoints(completion: @escaping (_:Int)->()) {

   loadPointsCompleted{(sum) in

        //HERE YOU CAN USE THE RESULT OF loadPointsCompleted

        //I CALLED IT sum



    loadPointsRedeemed{ (pointsRedeemedAsInt) in

          // HERE YOU CAN USE THE RESULT OF loadPointsRedeemed

           //I CALLED IT pointsRedeemedAsInt

          let balance = sum - pointsRedeemedAsInt

          completion(balance)

     }       

 }



}

To call the balance function wherever you want:

       balanceOfPoints{ (balance) in

           // Whatever you want with balance

       }

If you change the view ( for example you set some label text ), be sure to use the functions in the main thread.

The problem is that you are trying to access variables outside the scope of BalanceOfPoints().

Try returning the values you want to use in the equation from the first two functions, loadPointsRedeemed() and LoadPointsCompleted(). This can be done like so:

First Function

func loadPointsRedeemed() -> Int {



    databaseReference = Database.database().reference()



    let userID = Auth.auth().currentUser?.uid



    databaseReference.child("Users").child(userID!).observe(DataEventType.value, with: { (snapshot) in



        let value = snapshot.value as? NSDictionary



        // let Points_Earn = value?["Points_Earned"] as? String ?? ""

        let Points_Redeem = value?["Points_Redeemed"] as? String ?? ""





        // self.Points_Earned.text = Points_Earn

        self.Points_Redeemed.text = Points_Redeem



        let pointsRedeemedAsInt:Int = Int(Points_Redeem)!



        // Do any additional setup after loading the view.



        return pointsRedeemedAsInt



    }



)}

Second Function

func loadPointsCompleted() -> Int {



    self.challengeList.removeAll()



    databaseReference = Database.database().reference()



    let userID = Auth.auth().currentUser?.uid



    let refChallenges = Database.database().reference(withPath: "Challenges").child(userID!).queryOrdered(byChild: "Status").queryEqual(toValue: "Complete")



    refChallenges.observeSingleEvent(of: .value, with: { (snapshot) in



        //if the reference have some values

        if snapshot.childrenCount > 0 {



            //clearing the list

            self.challengeList.removeAll()



            //iterating through all the values

            for Challenges in snapshot.children.allObjects as! [DataSnapshot] {

                //getting values

                let challengeObject = Challenges.value as? [String: AnyObject]

                let Points = challengeObject?["Points"] as! Int



                //creating challenge object with model and fetched values

                let challenge = pointsModel(Points: (Points as Int?)!)



                //appending it to list

                self.challengeList.append(challenge)



            }   



            let sumOfPointsCompleted = self.challengeList.reduce(0) {$0 + $1.Points}



            let sumOfPointsCompletedString = String(sumOfPointsCompleted)

            self.Calc_Earned.text = sumOfPointsCompletedString



            return sumOfPointsCompleted



        }

    }   

)}

Third Function

func balanceOfPoints() -> Int {



    let sum = loadPointsCompleted()

    let pointsRedeemedAsInt = loadPointsRedeemed()



    let balance = sum - pointsRedeemedAsInt



    return balance



}

Now, wherever you call the functions loadPointsRedeemed() and loadPointsCompleted(), replace these calls with balanceOfPoints.

Notice the main changes I made to your code are adding return values to your functions so they can be used in other areas of your code. Check out the Swift Functions Documentation to learn more.