ios - Swift Image retrieving from Parse sdk - getting crashed

Question

I'm retrieving set of images from Parse, using the following code using Swift.

var imageResources : Array<UIImage> = []
override func viewDidLoad(){
    super.viewDidLoad()
    self.loadImages()
}

func loadImages(){

    var query = PFQuery(className: "Images")
    query.orderByDescending("objectId")

    query.findObjectsInBackgroundWithBlock ({(objects:[AnyObject]!, error: NSError!) in
        if(error == nil){            

            for object : PFObject! in objects as [PFObject] {                

                var thumbNail = PFFile()
                thumbNail = object["image"] as PFFile
                println("thumNail (thumbNail)")
                thumbNail.getDataInBackgroundWithBlock({
                   (imageData: NSData!, error: NSError!) in
                   if (error == nil) {
                        let image : UIImage = UIImage(data:imageData)
                        //image object implementation
                        self.imageResources.append(image)
                    }

                })//getDataInBackgroundWithBlock - end

            }//for - end

        }
        else{
            println("Error in retrieving (error)")
        }

    })//findObjectsInBackgroundWithblock - end


}

My Parse Class detail

class name - Images

When I run this function, it's getting crashed without a message in the console.

Note: I'm able to get the collection of PFFile objects in the callback.

I've replaced "thumbNail.getDataInBackgroundWithBlock({...." block with the synchronous function call thumbNail.getData() like "var imageData= thumbNail.getData() var image = UIImage(data:imageData)"

Then the error says

Warning: A long-running operation is being executed on the main thread. Break on warnBlockingOperationOnMainThread() to debug.

So, I reverted to thumbNail.getDataInBackGroundWithBloack({... But now, there is no error display in the console, as it happens before. Is there anything wrong in my approach please let me know. Any help would be appreciated...!

Answer 1

I managed to recreate the error, which seems to be some kind of memory leak / zombie on a PFObject. I'm not sure exactly why, but refactoring your code in the following manner got rid of the error in my case:

func loadImages() {

    var query = PFQuery(className: "Images")
    query.orderByDescending("objectId")


    query.findObjectsInBackgroundWithBlock ({(objects:[AnyObject]!, error: NSError!) in
        if(error == nil){

            self.getImageData(objects as [PFObject])

        }
        else{
            println("Error in retrieving (error)")
        }

    })//findObjectsInBackgroundWithblock - end


}

func getImageData(objects: [PFObject]) {
    for object in objects {

        let thumbNail = object["image"] as PFFile

        println(thumbNail)

        thumbNail.getDataInBackgroundWithBlock({
            (imageData: NSData!, error: NSError!) -> Void in
            if (error == nil) {
                let image = UIImage(data:imageData)
                //image object implementation
                self.imageResources.append(image)
                println(image)
            }

        })//getDataInBackgroundWithBlock - end

    }//for - end
}

EDIT: Incidentally, this also works:

func loadImages() {

    var query = PFQuery(className: "Images")
    query.orderByDescending("objectId")


    query.findObjectsInBackgroundWithBlock ({(objects:[AnyObject]!, error: NSError!) in
        if(error == nil){

            let imageObjects = objects as [PFObject]

            for object in objects {

                let thumbNail = object["image"] as PFFile

                thumbNail.getDataInBackgroundWithBlock({
                    (imageData: NSData!, error: NSError!) -> Void in
                    if (error == nil) {
                        let image = UIImage(data:imageData)
                        //image object implementation
                        self.imageResources.append(image)
                        println(image)
                    }

                })//getDataInBackgroundWithBlock - end

            }//for - end

        }
        else{
            println("Error in retrieving (error)")
        }

    })//findObjectsInBackgroundWithblock - end


}

This would indicate that the error was due to the following line:

for object : PFObject! in objects as [PFObject] {

Rewriting that line as follows:

for object : PFObject in objects as [PFObject] {

Also removes the error. So the reason for this error seems to be that that you told the program to unwrap something that wasn't an optional.