Declaring variable inside function not updating outside swift - swift

Question

I have a function where it goes into firebase data base and pulls the amount of items I have stored. It returns three when I print the variable postCount in the function itself but when I print it anywhere else it only has zero. It doesn't seem to be updating the global value.
import UIKit
import Firebase
class ViewController: UIViewController, iCarouselDataSource, iCarouselDelegate {
var items: [Int] = []
var postCount = 0
#IBOutlet var carousel: iCarousel!
func getData() {
Database.database().reference().child("Posts").observeSingleEvent(of: .value, with: { (snapshot) in
if let dict2 = snapshot.value as? [String: AnyObject] {
self.postCount = dict2.count
}
//This prints 3
print(self.postCount)
})
}
override func awakeFromNib() {
super.awakeFromNib()
print(self.postCount)
for i in 0 ... 99 {
items.append(i)
}
}
override func viewDidLoad() {
super.viewDidLoad()
getData()
print(self.postCount)
carousel.type = .cylinder
}
func numberOfItems(in carousel: iCarousel) -> Int {
return postCount
}
func carousel(_ carousel: iCarousel, viewForItemAt index: Int, reusing view: UIView?) -> UIView {
var label: UILabel
var itemView: UIImageView
//reuse view if available, otherwise create a new view
if let view = view as? UIImageView {
itemView = view
//get a reference to the label in the recycled view
label = itemView.viewWithTag(1) as! UILabel
} else {
//don't do anything specific to the index within
//this `if ... else` statement because the view will be
//recycled and used with other index values later
itemView = UIImageView(frame: CGRect(x: 0, y: 0, width: 200, height: 400))
itemView.image = UIImage(named: "page.png")
itemView.layer.borderWidth = 10
itemView.contentMode = .center
label = UILabel(frame: itemView.bounds)
label.backgroundColor = .clear
label.textAlignment = .center
label.font = label.font.withSize(50)
label.tag = 1
itemView.addSubview(label)
}
//set item label
//remember to always set any properties of your carousel item
//views outside of the `if (view == nil) {...}` check otherwise
//you'll get weird issues with carousel item content appearing
//in the wrong place in the carousel
label.text = "\(items[index])"
return itemView
}
func carousel(_ carousel: iCarousel, valueFor option: iCarouselOption, withDefault value: CGFloat) -> CGFloat {
if (option == .spacing) {
return value * 1.1
}
return value
}
}

Answer 1

I believe it is because retrieving data from Firebase is asynchronous. getData() is called and then instantly after that you print(self.postCount), even though getData() is still retrieving the data from Firebase.
Try changing the print(self.postCount) within getData() to
print("Data Loaded and there are \(self.postCount) posts")
and you should see in your log that the print(self.postCount) within viewDidLoad() is called before the print within getData(). As a result, when print(self.postCount) in viewDidLoad() is called, postCount still equals the default value of 0 since getValue() has not completed running even though that print is on the line after getData().
You probably want to call whatever functions that need to use the updated postCount inside the closure in getData() so that you ensure those functions use the updated postCount.
For example:
func getData() {
Database.database().reference().child("Posts").observeSingleEvent(of: .value, with: { (snapshot) in
if let dict2 = snapshot.value as? [String: AnyObject] {
self.postCount = dict2.count
}
print(self.postCount)
//everything within this closure will have the updated value of postCount
foo()
})
}
func foo() {
if self.postCount > 0 {
print("Lots of posts!")
}
else {
print("No posts :(")
}
}