Profile picture in cell not updating correctly - ios

Question

I have a PFQueryTableViewController populated by comments from different users. Each user has a profile picture stored on the Parse database. After loading each comment into a cell, I query the PFUser class to retrieve the profile picture of the user who posted the comment and add it to the cell. I also use PFCachePolicy to cache the profile picture to the device's memory so that displaying new cells with new profile pictures is a smoother transition.
However this is not the case. When a user posts a new comment and a new cell is added, the profile pictures shuffle around and takes about two seconds or so to update with the right image (probably because the table is re-queried and updated). I am trying to achieve something similar to iMessage or WhatsApp where the profile picture remained 'fixed' in the cell.
I am not sure what the problem is or if there is a better way to do this?
// get objectId of the user who posted a comment
let senderId = object?["Users"]!.objectId as String!
// query PFUser class using senderId to retrieve profile picture
var senderImage:PFQuery = PFUser.query()!
senderImage.cachePolicy = PFCachePolicy.CacheThenNetwork
senderImage.getObjectInBackgroundWithId(senderId){
(sender: PFObject?, error: NSError?) -> Void in
if error == nil && sender?.objectForKey("profilePicture") != nil {
let thumbnail = sender?.objectForKey("profilePicture") as? PFFile
thumbnail?.getDataInBackgroundWithBlock({
(imageData: NSData?, error: NSError?) -> Void in
if error == nil {
imageView.image = UIImage(data:imageData!)
} else {
println(error)
}
})
}
}

Answer 1

That's because you're not waiting until the images are finished loading when you update the UIImageView. Try Using this code:
var query = PFQuery(className:"Users")
query.findObjectsInBackgroundWithBlock {
(objects: [AnyObject]?, error: NSError?) -> Void in
if error == nil {
// The find succeeded.
self.scored = objects!.count
// Do something with the found objects
if let objects = objects as? [PFObject] {
for object in objects {
let userImageFile = object["Image"] as! PFFile
userImageFile.getDataInBackgroundWithBlock {
(imageData: NSData?, error: NSError?) -> Void in
if error == nil {
if let imageData = imageData {
let image = UIImage(data:imageData)
self.imageArray.append(image!)
}
}
dispatch_async(dispatch_get_main_queue()) {
//don't reload image view here!
}
}
}
}
} else {
// Log details of the failure
print("Error: \(error!) \(error!.userInfo)")
}
dispatch_async(dispatch_get_main_queue()) {
//wait until here to reload the image view
if self.imageArray.isEmpty == false {
//image array is not empty
self.ImageView.image = imageArray.first
}
else {
//no images found in parse
}
}