Memory warning on iOS 8 App - but usage is low

Question

I hope someone can help me out, I already searched Stackoverflow and Google but I couldn't get the right solution. I am having a very simple app which takes a photo (using the standard iOS Camera through UIImagePickerController) then I save it to the file system with a very low resolution - let thumbNailData = UIImageJPEGRepresentation(image, 0.02) after that I display the images in a collection view using Core Data - I only save the filename in Core Data, not the image, image is only in the filesystem. So, however, when I run the app it shows me a memory usage of not more than 15 MB and Process is around 1-2 %. Everything runs fine but after adding 6-7 Photos I get strange errors like the Memory Warning, Lost connection to my iPhone and this on:

Communications error: <OS_xpc_error: <error: 0x198adfa80> { count = 1, contents =
    "XPCErrorDescription" => <string: 0x198adfe78> { length = 22, contents = "Connection interrupted"

So, I am really stuck is I thought I made it very lightweight and then I get these errors.... I already submitted a note taking app to the App Store which was much more high functionality than this one but this one runs very stable...

Any ideas?

Here is some of my code: // Here I load the picture names into an array to display in the collection view

func loadColl () {
        let appDelegate = (UIApplication.sharedApplication().delegate as AppDelegate)
        let context:NSManagedObjectContext = appDelegate.managedObjectContext!
        let fetchRequest:NSFetchRequest = NSFetchRequest(entityName: "PictureNote")
        var error:NSError?
        var result = context.executeFetchRequest(fetchRequest, error: &error) as [PictureNote]

        for res in result {
            println(res.latitude)
            println(res.longitude)
            println(res.longDate)
            println(res.month)
            println(res.year)
            println(res.text)
           pictures.append(res.thumbnail)
        }

    }

// Here is the code to display in collection view

func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {

        let myImageCell:ImageCell = myCollectionView.dequeueReusableCellWithReuseIdentifier("imageCell", forIndexPath: indexPath) as ImageCell
        myImageCell.imageCell.image = self.loadImageFromPath(fileInDocumentsDirectory(self.pictures[indexPath.row]))
        return myImageCell
    }

// Here is the code to load the pictures from disk

func loadImageFromPath(path: String) -> UIImage {
    let image = UIImage(contentsOfFile: path)
    if image == nil {
        self.newAlert("Error loading your image, try again", title: "Notice")
    }
    return image!
}

// Here is my saving code

func saveNewEntry () {
        var unique = NSUUID().UUIDString
        var imageTitle = "Picture\(unique).jpg"
        var image = self.pickedImageView.image
        var path = fileInDocumentsDirectory(imageTitle)
        var thumbImageTitle = "ThumbPicture\(unique).jpg"
        var thumbPath = fileInDocumentsDirectory(thumbImageTitle)
        if self.saveImage(image!, path: path) == true && self.saveThumbImage(image!, thumbPath: thumbPath) == true {
            // Create the saving context
            let context = (UIApplication.sharedApplication().delegate as AppDelegate).managedObjectContext!
            let entityOne = NSEntityDescription.entityForName("PictureNote", inManagedObjectContext: context)
            let thisTask = PictureNote(entity: entityOne!, insertIntoManagedObjectContext: context)
            // Get all the values here
            self.getMyLocation()
            var theDate = NSDate()
            thisTask.month = Date.toString(date: theDate, format: "MM")
            thisTask.year = Date.toString(date: theDate, format: "yyyy")
            thisTask.longDate = theDate
            thisTask.longitude = getMyLocation()[1]
            thisTask.latitude = getMyLocation()[0]
            thisTask.text = self.noteTextView.text
            thisTask.imageURL = imageTitle
            thisTask.thumbnail = thumbImageTitle
            thisTask.id = unique
            // Saving to CoreData
            if context.save(nil) {
                self.newAlert("Saving your note was successful!", title: "Notice")
                self.noteTextView.text = ""
            } else {
                 self.newAlert("Error saving your note, try again", title: "Notice")
            }

        } else {

          self.newAlert("Error saving your image, try again", title: "Notice")
        }


        self.pickedImageView.image = UIImage(named: "P1000342.jpg")
    }

I am really thankful for every suggestion....if you need more code, just let me know...

Answer 1

I notice that you are using a dramatically reduced quality factor in conjunction with UIImageJPEGRepresentation. If this is an attempt is to reduce the memory involved, all that does is reduce the size of the resulting NSData your write to persistent storage, but loading that image into the image view will still require something on the order of (4 × width × height) bytes (note, that's the dimensions of the image, not the image view). Thus the 3264 × 2448 image from a iPhone takes up 30mb per image, regardless of the quality factor employed by UIImageJPEGRepresentation.

Usually I will make sure my collection/table view uses thumbnail representation (either the thumbnail property of the ALAsset or resize the default representation myself). If I'm caching this thumbnail anywhere (such as persistent storage suggested by your question), I can then use a high quality representation of the thumbnail (I use PNG because it's lossless with compression, but JPEG with 0.7-0.9 quality factor is a reasonably faithful version, too).