iOS Swift Adding Object To Array - ios

Question

I am trying to add the retrieved object from Parse to an array. It has found the user, it is printed in my logs. All the key names match up, I can't seem to find why both my userArray and imageFiles array are printed to the logs as empty. Thanks for the help!
var userArray: [String] = []
var refresher: UIRefreshControl!
var imageFiles = [PFFile]()
override func viewDidLoad() {
super.viewDidLoad()
PFGeoPoint.geoPointForCurrentLocationInBackground { (geopoint: PFGeoPoint!, error: NSError!) -> Void in
if error == nil {
println(geopoint)
var user = PFUser.currentUser()
user["location"] = geopoint
user.save()
var query = PFUser.query()
query.whereKey("location", nearGeoPoint:geopoint)
query.limit = 10
query.findObjectsInBackgroundWithBlock({ (users: [AnyObject]!, error: NSError!) -> Void in
for user in users {
self.userArray.append(user["name"] as! String)
self.imageFiles.append(user["profilePicFile"] as! PFFile)
println(user)
}
})
}
}
self.refresher = UIRefreshControl()
self.refresher.attributedTitle = NSAttributedString(string: "Pull to refresh")
self.refresher.addTarget(self, action: "refresh", forControlEvents: UIControlEvents.ValueChanged)
self.tableView.addSubview(self.refresher)
//follow udemy to get pull to refresh , need update users
println(userArray)
println(imageFiles.count)
}
func updateUsers() {
self.userArray.removeAll(keepCapacity: true)
self.imageFiles.removeAll(keepCapacity: true)
var aquery = PFUser.query()
aquery.whereKey("username", equalTo: PFUser.currentUser().username)
var cools = aquery.findObjects()
var query = PFUser.query()
query.whereKey("location", nearGeoPoint: cools[0]["location"] as! PFGeoPoint!)
query.limit = 10
query.findObjectsInBackgroundWithBlock({ (users: [AnyObject]!, error: NSError!) -> Void in
for user in users {
self.userArray.append(user["name"] as! String)
self.imageFiles.append(user["profilePicFile"] as! PFFile)
}
self.tableView.reloadData()
self.refresher.endRefreshing()
})
}

Answer 1

The reason is because PFGeoPoint.geoPointForCurrentLocationInBackground is an asynchronous method that takes a callback closure as a parameter to fire off as soon as the asynchronous work is done. So viewDidLoad will call that method but continue on and print userArray before the geoPointForCurrentLocationInBackground callback gets fired.
This is a big feature of functional programming languages so I suggest reading up on closures when you can.
http://code.tutsplus.com/tutorials/swift-from-scratch-closures--cms-23138
https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Closures.html
If you put the println statements after you iterate the users inside of the callback, you will see your data:
for user in users {
self.userArray.append(user["name"] as! String)
self.imageFiles.append(user["profilePicFile"] as! PFFile)
println(user)
}
}
println(userArray) // you will see userArray is populated
println(imageFiles.count)