Better way to retrieve multiple images from Parse - ios

Question

Noob question here and I know my code below is very wrong but it works in that it retrieves the 3 images I need. However, I'd like to know a better way to retrieve multiple images from Parse.
Any help would be greatly appreciated!
func retrieveImage() {
var query = PFQuery(className: "Items")
query.orderByDescending("createdAt")
query.findObjectsInBackgroundWithBlock { (objects: [AnyObject]?, error: NSError?) -> Void in
if error == nil {
let imageObjects = objects as! [PFObject]
for (index, object) in enumerate(imageObjects) {
let thumbnail1 = object["image1"] as! PFFile
let thumbnail2 = object["image2"] as! PFFile
let thumbnail3 = object["image3"] as! PFFile
thumbnail1.getDataInBackgroundWithBlock{(imageData: NSData?, error: NSError?) -> Void in
if error == nil {
if let image = UIImage(data: imageData!) {
self.itemImages[index] = image
}
}
thumbnail2.getDataInBackgroundWithBlock{(imageData: NSData?, error: NSError?) -> Void in
if error == nil {
if let image = UIImage(data: imageData!) {
self.itemImages2[index] = image
}
}
}
thumbnail3.getDataInBackgroundWithBlock{(imageData: NSData?, error: NSError?) -> Void in
if error == nil {
if let image = UIImage(data: imageData!) {
self.itemImages3[index] = image
}
}
}
}
}
}
}
}

Answer 1

First the idea... we want to do an arbitrarily long list of asynch tasks, collect their results, and be notified on completion or error. We do this by parameterizing the task (in this case, the PFFiles whose contents are to be fetched are the parameters), and we use those parameters as a "to-do list".
A recursive function does the work, picking off the first item in the list, doing the asynch task, and then calling itself with the remainder of the list. An empty to-do list means we're done.
I've tried to translate the answer I referred to here into swift (literally learning the language line by line)....
func load(pfFiles: Array<PFFile>, var filling: Dictionary<PFFile, UIImage>, completion: (success: Bool) -> Void) {
completion(success: true)
var count = pfFiles.count
if (count == 0) {
return completion(success: true)
}
var file = pfFiles[0]
var remainder = Array(pfFiles[1..<count])
file.getDataInBackgroundWithBlock{(imageData: NSData?, error: NSError?) -> Void in
if error == nil {
if let image = UIImage(data: imageData!) {
filling[file.name] = image
self.load(remainder, filling: filling, completion: completion)
}
} else {
completion(success: false)
}
}
}
Given this is my first attempt, I'll be a little shocked and delighted if it works, but the algorithm is sound, and the swift compiles and appears to match the idea I outlined. Here's how to call it...
var pfFiles: Array<PFFile>
for (index, object) in enumerate(imageObjects) {
pfFiles.append(object["image1"])
pfFiles.append(object["image2"])
pfFiles.append(object["image3"])
}
var filling: Dictionary<String, UIImage>
// call the function here
// in the completion assign filling to property
// anytime after, when you have a PFFile like someObject["image2"]
// you use its name to look it up the UIImage in the results dictionary
Let me know if that last bit is clear enough. As you can see, I ran out of steam on my swift translation and resorted to pseudo code.

Answer 2

I believe you can just do self.itemImages[index] = thumbnail1.getData()!
If it crashs, do : query.includeKey("image1")
NOTE:
If you afraid to block the main queue, open a new thread to do such thing