Getting crash after picking images from UIImagePickerController (Related to memory leak?)

Question

I have been trying to minimize my memory footprint with UIImagePickerController, but I'm starting to think that the memory problems I am having are resulting from poor memory management, instead of a particular way to handle the UIImagePickerController object.

My workflow is this: The "Edit Image" button is clicked, which presents a UIActionSheet. This action sheet allows you to delete, take a picture, choose from the library, or cancel. If you select Choose from the library or Take Picture, I alloc an instance of UIImagePickerController and present it, followed by a release of UIImagePickerController:

-(void)actionSheet:(UIActionSheet *)actionSheet clickedButtonAtIndex:(NSInteger)buttonIndex
{
    if (actionSheet.tag != 999) {
        UIImagePickerController *imagePicker = [[UIImagePickerController alloc] init];
        imagePicker.delegate = self;

        BOOL pickImage = nil;

        if (actionSheet.tag == iPhoneWithDelete) {
            switch (buttonIndex) {
                case 0:
                    object.objectImage = nil;
                    pickImage = NO;
                    break;
                case 1:
                    imagePicker.sourceType = UIImagePickerControllerSourceTypeCamera;
                    pickImage = YES;
                    break;
                case 2:
                    imagePicker.sourceType = UIImagePickerControllerSourceTypeSavedPhotosAlbum;
                    pickImage = YES;
                    break;
                default:
                    pickImage = NO;
                    break;
            }
        } else if (actionSheet.tag == iPhoneNoDelete) {
            switch (buttonIndex) {
                case 0:
                    imagePicker.sourceType = UIImagePickerControllerSourceTypeCamera;
                    pickImage = YES;
                    break;
                case 1:
                    imagePicker.sourceType = UIImagePickerControllerSourceTypeSavedPhotosAlbum;
                    pickImage = YES;
                    break;
                default:
                    pickImage = NO;
                    break;
            }       
        } else if (actionSheet.tag == iPodWithDelete) {
            switch (buttonIndex) {
                case 0:
                    object.objectImage = nil;
                    pickImage = NO;
                    break;
                case 1:
                    imagePicker.sourceType = UIImagePickerControllerSourceTypeSavedPhotosAlbum;
                    pickImage = YES;
                    break;
                default:
                    pickImage = NO;
                    break;
            }
        } else if (actionSheet.tag == iPodNoDelete) {
            switch (buttonIndex) {
                case 0:
                    imagePicker.sourceType = UIImagePickerControllerSourceTypeSavedPhotosAlbum;
                    pickImage = YES;
                    break;
                default:
                    pickImage = NO;
                    break;
            }
        }

        if (pickImage) {
            imagePicker.allowsEditing = YES;
            [self presentModalViewController:imagePicker animated:YES];
        } else {
            [self setupImageButton];
            [self setupChooseImageButton];
        }
        [imagePicker release];
    }
}

Once I get a selection back from the UIImagePickerController, I save 2 images, a resized version of the edited image to use for a thumbnail, and a 800x600 version of the original unedited image into a relationship attribute (Transformational, using the same UIImage to PNG transformations found in the Recipes demo code) for display use: (the resize methods are based on the one demoed in this SO post.)

- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info
{

    [self dismissModalViewControllerAnimated:YES];

    NSManagedObject *oldImage = object.imageFull;
    if (oldImage != nil)
    {
        [object.managedObjectContext deleteObject:oldImage];
    }

    NSManagedObject *image = [NSEntityDescription insertNewObjectForEntityForName:@"Image" inManagedObjectContext:object.managedObjectContext];
    object.imageFull = image;

    UIImage *rawImage = [info objectForKey:@"UIImagePickerControllerOriginalImage"];

    CGSize size = CGSizeMake(800, 600);

    UIImage *fullImage = [UIImageManipulator scaleImage:rawImage toSize:size];

    [image setValue:fullImage forKey:@"imageFull"];

    UIImage *processedImage = [UIImageManipulator scaleImage:[info objectForKey:@"UIImagePickerControllerEditedImage"] toSize:CGSizeMake(75, 75)];
    object.objectImage = processedImage;
    [self setupImageButton];
    [self setupChooseImageButton];

    rawImage = nil;
    fullImage = nil;
    processedImage = nil;
}

When I go through viewDidUnload I am setting self.object = nil, and [object release] during dealloc, but I'm still getting memory warnings after about 10 image changes, with a crash at around 20. It leads me to believe that I am not getting that full image out of memory the correct way. What am I missing here?

And on a second note, does the Camera source use significantly more memory than the Photo Albums source? I tend to get more crashes when using the camera.

--EDIT--

Starting a bounty for any information about what I may be handling wrong. I will update this post with any answers to anything I have been unclear about. Just at my wit's end on this.

--EDIT 2--

Reworked the code to take chrissr's suggestions into account, and implemented GCD to improve usability. Is this as efficient as this process gets? Still getting memory warnings, and a crash around 20 images in. I'm sure that the combination of doing expensive UIImage resizing and using UIImagePickerController is murdering the CPU, but I can't imagine that every app is dealing with uncertainty around the UIImagePickerController. My memory footprint is around 2 megs. I have been operating under the assumption that that was plenty of overhead. Should I reduce that footprint further?

Here is the modified code:

- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info
{

    [self dismissModalViewControllerAnimated:YES];

    if (object.imagePath != nil) {
        [self deleteImages];
    }
    dispatch_queue_t image_queue;
    image_queue = dispatch_queue_create("com.gordonfontenot.app", NULL);

    dispatch_async(image_queue, ^{

        NSDate *now = [NSDate date];

        NSDateFormatter *f = [[NSDateFormatter alloc] init];
        [f setDateFormat:@"yyyyMMDDHHmmss"];

        NSString *imageName = [NSString stringWithFormat:@"Image-%@-%i", [f stringFromDate:now], arc4random() % 100];
        NSString *thumbName = [NSString stringWithFormat:@"%@-thumb", imageName];

        [f release];

        NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
        NSString *documentsDirectory = [paths objectAtIndex:0];

        NSString *fullPath = [documentsDirectory stringByAppendingPathComponent:imageName];
        NSString *thumbPath = [documentsDirectory stringByAppendingPathComponent:thumbName];

        NSData *thumbImageData = UIImagePNGRepresentation([UIImageManipulator scaleImage:[info objectForKey:@"UIImagePickerControllerEditedImage"] toSize:CGSizeMake(120, 120)]);
        [thumbImageData writeToFile:thumbPath atomically:NO];
        dispatch_async(dispatch_get_main_queue(), ^{
            object.thumbPath = thumbPath;
            [self setupImageButton];
            imageButton.enabled = NO;
            [self setupChooseImageButton];
        });
        NSData *fullImageData = UIImagePNGRepresentation([UIImageManipulator scaleImage:[info objectForKey:@"UIImagePickerControllerOriginalImage"] toSize:CGSizeMake(800, 600)]);
        [fullImageData writeToFile:fullPath atomically:NO];

        dispatch_async(dispatch_get_main_queue(), ^{
            imageButton.enabled = YES;
            object.imagePath = fullPath;
        });

        if (picker.sourceType == UIImagePickerControllerSourceTypeCamera) {
            UIImageWriteToSavedPhotosAlbum([info objectForKey:@"UIImagePickerControllerOriginalImage"], self, nil, nil);
        }

    });
    dispatch_release(image_queue);
}

Answer 1

Memory warnings are extremely common when dealing with the UIImagePickerController. This is especially true when using the camera. Keep in mind that while a JPG or PNG on disk may only amount to a few MB, the uncompressed in memory bitmap used to draw the image uses considerably more.

There's nothing that you're doing wrong necessarily, but some improvements can be made:

Rather than storing the image bytes in Core Data, why not write the image to disk and store the path to the file in your database?

Rather than using so many autoreleased images, can you find a way to manage their lifecycle directly and release them sooner?

Your best bet may be to write the images to disk as soon after processing as possible and free up the memory they're using. Then store their location using Core Data rather than the raw data.