Adding integers in for loop and printing the total - ios

Question

I am looping through integer objects and want to add each integer to an integer variable, then when the for-loop is done, print the total. Is there an easy way to do this? Right now, I can retrieve the objects and print them individually, but the total prints as 0 every time.
Please see the code below. This is for an app written in Swift with Parse as the backend.
Anything helps, and thank you!
var itemsArray = [Int]()
let followingUserItemsQuery = PFUser.query()
followingUserItemsQuery?.whereKey("objectId", equalTo: (PFUser.currentUser()?.objectId!)!)
followingUserItemsQuery?.findObjectsInBackgroundWithBlock({ (objects: [PFObject]?, error) in
if let objects = objects {
for object in objects {
let followingUsersArray = (object["following"] as! [String])
// Get number of listed items of following users with PFUser query for their total objects
for followingUser in followingUsersArray {
print(followingUser)
let query = PFUser.query()
query?.whereKey("objectId", equalTo: followingUser)
//Get each user's listedItems count then append to a higher-level integer variable
query?.getFirstObjectInBackgroundWithBlock({ (object, error) in
itemsArray.append(object!["listedItems"] as! Int)
})
}
}
}
let itemsSum = itemsArray.reduce(0, combine: +)
print(itemsSum)
self.followingUsersAddedItems.text = String("Your followers listed "+String(itemsSum)+" items")

Answer 1

Try this:
var count = 0
...
for followingUser in followingUsersArray {
count += object!["listedItems"] as! Int
}

Answer 2

Your code to reduce / combine the Int values is correct. The problem is that it runs before any of the nested asynchronous Parse queries complete and execute their callbacks. So at the time it runs, itemsArray is still empty. You will need to redesign your code so that itemsSum is calculated only after all the various nested Parse queries have all completed.