Capturing a value from closure in Swift with Parse - ios

Question

I am creating an app for test taking in Swift, and I'm using Parse to handle the backend. There are two main "object" types that I am working with in Parse: Test and Question. Each Test object contains an array of Question objects called "questions". I need to capture the questions array of the test object with the getObjectInBackgroundWithId method, as I have the test's objectId value, and save it to an array I have declared earlier in the method. When I assign the array to my questions array from the beginning of the method inside of the closure, I print it, and it appears to have been correctly copied, but when I print it outside of the closure, it hasn't been copied. Here is the method:
#IBAction func endTestPressed(sender: UIButton)
{
let lab = self.pinLabel.text!
var questions = [PFObject]()
let query = PFQuery(className:"Test")
query.getObjectInBackgroundWithId(lab.substringFromIndex(advance(lab.startIndex,5)))
{
(test: PFObject?, error: NSError?) -> Void in
if error == nil && test != nil
{
questions = test?["questions"] as! [PFObject]
print("Inside of closure: \(questions)")
}
else
{
print(error)
}
}
print("Outside of closure: \(questions)")
}
How can I save the array from Parse as an array declared in the method before the closure?

Answer 1

It is not that the array is empty in the outside the closure, what happens is that getObjectInBackgroundWithId happens in the background, the rest of your app still running, so you first print the outside println command, than when the results come back from the background thread it just run the completion block
#IBAction func endTestPressed(sender: UIButton)
{
let lab = self.pinLabel.text!
var questions = [PFObject]()
let query = PFQuery(className:"Test")
query.getObjectInBackgroundWithId(lab.substringFromIndex(advance(lab.startIndex,5)))
{
//Run when the getObjectInBackgroundWithId return with the results
(test: PFObject?, error: NSError?) -> Void in
if error == nil && test != nil
{
questions = test?["questions"] as! [PFObject]
print("Inside of closure: \(questions)") //this happen after the print outside the closure as the request happens in the backgroun
}
else
{
print(error)
}
}
//Application continue run while the getObjectInBackgroundWithId retrives data from Parse.com
print("Outside of closure: \(questions)") //This will happen first and the array is not populate yet
}