Swift Variables Scope Issue - ios

Question

I declare arr1 and arr2 as arrays globally in my viewcontroller.
In the following function, I add to them in a parse query. Xcode gets buggy when I don't include "self" before arr1 inside the query, so I included it. Outside the query, in the space where I have marked below, I try to access arr1 and arr2. But regardless of whether I try self.arr1 or arr1, the array turns out to be empty at that point. I think this is some sort of scope issue with swift, and I've had quite a bit of trouble with it so any help would be much appreciated.
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
if (segue.identifier == "vF") {
var destVC = segue.destinationViewController as vF
destVC.namePassed = fV
var query = PFQuery(className:"class")
query.whereKey("createdBy", equalTo:fV)
query.findObjectsInBackgroundWithBlock {
(objects: [AnyObject]!, error: NSError!) -> Void in
if error == nil {
// The find succeeded.
NSLog("Successfully retrieved \(objects.count) records.")
// Do something with the found objects
for object in objects {
self.arr1.append(object["field1"]! as Int)
self.arr2.append(object["field2"]! as String)
}
} else {
// Log details of the failure
}
}
// I want to access arr1 and arr2 right here, but when I do they come up empty
// I have tried accessing with self.arr1 and arr1 but neither works
}
}

Answer 1

The findObjectsInBackgroundWithBlock is async so it will happen in the background thread while your program still running in the main thread, by the point your background thread comeback with the data you need you program is why passed the point you indicate.
One of the best solutions for your problem is to add observers for the arr1 and arr2 so you will be notified when it happens. Add observers to array can be a little bit trick and I want to keep it simple for you, so I would recommend you to create a boolean variable that tells you when the value finish change. To do so you will need to create the variable like this
var arrayDidChange:Bool = false {
didSet{
if arrayDidChange{
callFuncDataReadArrayHere()
}
}
}
Now everytime you change the values (add or edit) in the array you set arrayDidChange to true and in the end of callFuncDataReadArrayHere after do all you need to do you set arrayDidChange to false.
This way you will always be sure you will access the values in the array after it be populate.
I hope that helped you!

Answer 2

You should connect the segue directly from the controller instead of the cell. Implement didSelectRowAtIndexPath, and put the query there, and call performSegueWithIdentifier:sender: inside the completion block of the asynchronous method. Now, when you implement prepareForSegue, the arrays will be available to pass to the destination view controller.
override func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
var query = PFQuery(className:"class")
query.whereKey("createdBy", equalTo:fV)
query.findObjectsInBackgroundWithBlock {
(objects: [AnyObject]!, error: NSError!) -> Void in
if error == nil {
// The find succeeded.
NSLog("Successfully retrieved \(objects.count) records.")
// Do something with the found objects
for object in objects {
self.arr1.append(object["field1"]! as Int)
self.arr2.append(object["field2"]! as String)
}
self.performSegueWithIdentifier("vF", sender: self)
} else {
// Log details of the failure
}
}
}
There will be some delay before the segue actually proceeds with this approach, because it won't happen until findObjectsInBackgroundWithBlock returns its results. If that's not acceptable, then you could still pass the arrays in prepareForSegue (in the same place I show after the "for object in objects" clause), but then the arrays will not be immediately available in the destination view controller, and you will have to deal with that.