UITableView in Parse, not indexing properly - ios

Question

All,
I have a simple class in the parse backend - which feeds a uitableview. The data is stored in Arrays. I guess because all parse data is done in the background sometimes data gets downloaded before others. I have a very mixed up tableview. With images in the wrong cell etc. Also the custom cells are sometimes not showing up at all and I need to do a refresh.
Here is my code that I used to download all the data from parse and add into the arrays.
Can you have a look please and suggest a way to do this.
Also how can I add a placeholder image , before the original image comes up.
Also this code is in my ViewDidLoad, would it be better in an earlier function, hopefully so i don't have to relsoaddata on the tableview..
var query = PFQuery(className:"TableViewData")
query.includeKey("EventLoc")
query.findObjectsInBackgroundWithBlock{
(objects: [AnyObject]!, error: NSError!) -> Void in
if error == nil {
for object in objects {
let thumbNail = object["backgroundImage"] as PFFile
thumbNail.getDataInBackgroundWithBlock({
(imageData: NSData!, error: NSError!) -> Void in
if (error == nil) {
dispatch_async(dispatch_get_main_queue()) {
let image = UIImage(data:imageData)
self.CellBackgroundImage.append(image!)
}
}
})
var VenueLocation = object["EventLoc"] as PFObject!
VenueLocation.fetchIfNeededInBackgroundWithBlock {
(VenueLocation: PFObject!, error: NSError!) -> Void in
dispatch_async(dispatch_get_main_queue()) {
let VenueLocationTitle = VenueLocation["EventLocation"] as NSString
self.EventLocationArray.append(VenueLocationTitle)
}
}
let eventiconimage = object["EventIcon"] as PFFile
eventiconimage.getDataInBackgroundWithBlock({
(imageData: NSData!, error: NSError!) -> Void in
if (error == nil) {
dispatch_async(dispatch_get_main_queue()) {
let image = UIImage(data:imageData)
self.EventIconImageArray.append(image!)
}
}
})
dispatch_async(dispatch_get_main_queue()) {
self.TitleArray.append(object["EventTitle"] as String)
self.EventPriceArray.append(object["EventPrice"] as String)
self.EventStartDate.append(object["EventStartDate"] as NSDate)
self.EventEndDate.append(object["EventEndDate"] as NSDate)
self.tableView.reloadData()
}

Answer 1

You need to use serial queue then your array data will be in order. Whats happening because of concurrent task the data is not appended in order
var backgroundQueue:dispatch_queue_t = dispatch_queue_create("SerialQueue", DISPATCH_QUEUE_SERIAL)
var query = PFQuery(className:"TableViewData")
query.includeKey("EventLoc")
query.findObjectsInBackgroundWithBlock{
(objects: [AnyObject]!, error: NSError!) -> Void in
if error == nil {
for object in objects {
dispatch_async(backgroundQueue, { () -> () in
let thumbNail = object["backgroundImage"] as PFFile
thumbNail.getDataInBackgroundWithBlock({
(imageData: NSData!, error: NSError!) -> Void in
if (error == nil) {
dispatch_async(dispatch_get_main_queue()) {
let image = UIImage(data:imageData)
self.CellBackgroundImage.append(image!)
}
}
})
var VenueLocation = object["EventLoc"] as PFObject!
VenueLocation.fetchIfNeededInBackgroundWithBlock {
(VenueLocation: PFObject!, error: NSError!) -> Void in
dispatch_async(dispatch_get_main_queue()) {
let VenueLocationTitle = VenueLocation["EventLocation"] as NSString
self.EventLocationArray.append(VenueLocationTitle)
}
}
let eventiconimage = object["EventIcon"] as PFFile
eventiconimage.getDataInBackgroundWithBlock({
(imageData: NSData!, error: NSError!) -> Void in
if (error == nil) {
dispatch_async(dispatch_get_main_queue()) {
let image = UIImage(data:imageData)
self.EventIconImageArray.append(image!)
}
}
})
dispatch_async(dispatch_get_main_queue()) {
self.TitleArray.append(object["EventTitle"] as String)
self.EventPriceArray.append(object["EventPrice"] as String)
self.EventStartDate.append(object["EventStartDate"] as NSDate)
self.EventEndDate.append(object["EventEndDate"] as NSDate)
self.tableView.reloadData()
}
});
}
}