Cannot index empty buffer in Swift - ios

Question

I'm following along with Rob Percival's tutorial on Udemy and my app crashes with a fatal error: cannot index empty buffer.
The error happens on the following line in the ViewdidLoad method:
userImage.image = UIImage(data: self.userImages[0])
Using println(self.userImages) right above that erroneous line I found out the array is empty. The console outputs a []. This must be why it's crashing. Correct?
My Parse.com dashboard shows that all my users have images. I'm not sure why the array would be empty. Any ideas?
import UIKit
class SwipeViewController: UIViewController {
var xFromCenter: CGFloat = 0
var usernames = [String]()
var userImages = [NSData]()
var currentUser = 0
override func viewDidLoad() {
super.viewDidLoad()
println(PFUser.currentUser()["first_name"])
PFGeoPoint.geoPointForCurrentLocationInBackground { (geopoint: PFGeoPoint!, error: NSError!) -> Void in
println(error)
if error == nil {
println(geopoint)
var user = PFUser.currentUser()
user["location"] = geopoint
var query = PFUser.query()
query.whereKey("location", nearGeoPoint:geopoint)
query.limit = 10
query.findObjectsInBackgroundWithBlock({ (users, error) -> Void in
for user in users {
var gender1 = user["gender"] as? NSString
var gender2 = PFUser.currentUser()["interestedIn"] as? NSString
if gender1 == gender2 && PFUser.currentUser().username != user.username {
self.usernames.append(user.username)
// Update - chaned as to as!
self.userImages.append(user["image"] as NSData)
}
}
var userImage: UIImageView = UIImageView(frame: CGRectMake(0, 0, self.view.frame.width, self.view.frame.height))
println("images:")
println(userImage)
println(self.userImages)
userImage.image = UIImage(data: self.userImages[0])
userImage.contentMode = UIViewContentMode.ScaleAspectFit
self.view.addSubview(userImage)
var gesture = UIPanGestureRecognizer(target: self, action: Selector("wasDragged:"))
userImage.addGestureRecognizer(gesture)
userImage.userInteractionEnabled = true
})
user.save()
}
}
}
func wasDragged(gesture: UIPanGestureRecognizer) {
let translation = gesture.translationInView(self.view)
var label = gesture.view!
xFromCenter += translation.x
var scale = min(100 / abs(xFromCenter), 1)
label.center = CGPoint(x: label.center.x + translation.x, y: label.center.y + translation.y)
gesture.setTranslation(CGPointZero, inView: self.view)
var rotation:CGAffineTransform = CGAffineTransformMakeRotation(xFromCenter / 200)
var stretch:CGAffineTransform = CGAffineTransformScale(rotation, scale, scale)
label.transform = stretch
if label.center.x < 100 {
println("Not Chosen")
} else if label.center.x > self.view.bounds.width - 100 {
println("Chosen")
}
if gesture.state == UIGestureRecognizerState.Ended {
self.currentUser++
label.removeFromSuperview()
if self.currentUser < self.userImages.count {
var userImage: UIImageView = UIImageView(frame: CGRectMake(0, 0, self.view.frame.width, self.view.frame.height))
userImage.image = UIImage(data: self.userImages[self.currentUser])
userImage.contentMode = UIViewContentMode.ScaleAspectFit
self.view.addSubview(userImage)
var gesture = UIPanGestureRecognizer(target: self, action: Selector("wasDragged:"))
userImage.addGestureRecognizer(gesture)
userImage.userInteractionEnabled = true
xFromCenter = 0
} else {
println("No more users")
}
}
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
/*
// MARK: - Navigation
// In a storyboard-based application, you will often want to do a little preparation before navigation
override func prepareForSegue(segue: UIStoryboardSegue!, sender: AnyObject!) {
// Get the new view controller using segue.destinationViewController.
// Pass the selected object to the new view controller.
}
*/
}

Answer 1

Looks like a data issue. The problem must comes from the loop just above the failing line.
Conditions are not met, and so no image is pushed into the array. Reasons can be:
You only have 1 user (your current user)
There is no other users with a gender that meets the "interested in" condition of your current user
Your users (current or not) doesn't have the "gender" or "interestedIn" attributes set
The best way is to put breakpoint (or log) inside your loop in order to determine users gender and "interestedIn" attributes and see if there is some matches.