Memory issue while fetching images from Photos library with metadata

Question

I'm trying to get all photos from photos library with image's metadata. It works fine for 10-20 images but when there are 50+ images it occupies too much memory, which causes to app crash.

Why i need all images into array?
Answer - to send images to server app. [i'm using GCDAsyncSocket to send data on receiver socket/port and i don't have that much waiting time to request images from PHAsset while sending images on socket/port.

My Code :

+(void)getPhotosDataFromCamera:(void(^)(NSMutableArray *arrImageData))completionHandler
{
    [PhotosManager checkPhotosPermission:^(bool granted)
    {
        if (granted)
        {
            NSMutableArray *arrImageData = [NSMutableArray new];

        NSArray *arrImages=[[NSArray alloc] init];

        PHFetchResult *result = [PHAsset fetchAssetsWithMediaType:PHAssetMediaTypeImage options:nil];

        NSLog(@"%d",(int)result.count);

        arrImages = [result copy];

        //--- If no images.
        if (arrImages.count <= 0)
        {
            completionHandler(nil);
            return ;
        }

        __block int index = 1;
        __block BOOL isDone = false;
        for (PHAsset *asset in arrImages)
        {
            [PhotosManager requestMetadata:asset withCompletionBlock:^(UIImage *image, NSDictionary *metadata)
             {
                 @autoreleasepool
                 {
                     NSData *imageData = metadata?[PhotosManager addExif:image metaData:metadata]:UIImageJPEGRepresentation(image, 1.0f);

                     if (imageData != nil)
                     {
                         [arrImageData addObject:imageData];
                         NSLog(@"Adding images :%i",index);

                         //--- Done adding all images.
                         if (index == arrImages.count)
                         {
                             isDone = true;
                             NSLog(@"Done adding all images with info!!");
                             completionHandler(arrImageData);
                         }
                         index++;
                     }
                 }
             }];
        }
    }
    else
    {
        completionHandler(nil);
    }
}];
}


typedef void (^PHAssetMetadataBlock)(UIImage *image,NSDictionary *metadata);

+(void)requestMetadata:(PHAsset *)asset withCompletionBlock:(PHAssetMetadataBlock)completionBlock
{
    PHContentEditingInputRequestOptions *editOptions = [[PHContentEditingInputRequestOptions alloc]init];
    editOptions.networkAccessAllowed = YES;
    [asset requestContentEditingInputWithOptions:editOptions completionHandler:^(PHContentEditingInput *contentEditingInput, NSDictionary *info)
     {
         CIImage *CGimage = [CIImage imageWithContentsOfURL:contentEditingInput.fullSizeImageURL];
         UIImage *image = contentEditingInput.displaySizeImage;

         dispatch_async(dispatch_get_main_queue(), ^{
             completionBlock(image,CGimage.properties);
         });

         CGimage = nil;
         image = nil;

     }];

    editOptions = nil;
    asset =nil;
}

+ (NSData *)addExif:(UIImage*)toImage metaData:(NSDictionary *)container
{



 NSData *imageData = UIImageJPEGRepresentation(toImage, 1.0f);
       // create an imagesourceref
    CGImageSourceRef source = CGImageSourceCreateWithData((__bridge CFDataRef) imageData, NULL);

// this is the type of image (e.g., public.jpeg)
CFStringRef UTI = CGImageSourceGetType(source);

// create a new data object and write the new image into it
NSMutableData *dest_data = [[NSMutableData alloc] initWithLength:imageData.length+2000];
CGImageDestinationRef destination = CGImageDestinationCreateWithData((__bridge CFMutableDataRef)dest_data, UTI, 1, NULL);

if (!destination) {
    NSLog(@"Error: Could not create image destination");
}

// add the image contained in the image source to the destination, overidding the old metadata with our modified metadata
CGImageDestinationAddImageFromSource(destination, source, 0, (__bridge CFDictionaryRef) container);
BOOL success = NO;
success = CGImageDestinationFinalize(destination);

if (!success) {
    NSLog(@"Error: Could not create data from image destination");
}

CFRelease(destination);
CFRelease(source);
imageData = nil;
source = nil;
destination = nil;

return dest_data;

}

Answer 1

There simply is not enough memory on the phone to load all of the images into the photo library into memory at the same time.

If you want to display the images, then only fetch the images that you need for immediate display. For the rest keep just he PHAsset. Make sure to discard the images when you don't need them any more.

If you need thumbnails, then fetch only the thumbnails that you need.

If want to do something with all of the images - like add a watermark to them or process them in some way - then process each image one at a time in a queue.

I cannot advise further as your question doesn't state why you need all of the images.

Answer 2

Well it's not a surprise that you arrive into this situation, since each of your image consumes memory and you instantiate and keep them in memory. This is not really a correct design approach. In the end it depends on what you want to do with those images.

What I would suggest is that you keep just the array of your PHAsset objects and request the image only on demand. Like if you want to represent those images into a tableView/collectionView, perform the call to

[PhotosManager requestMetadata:asset withCompletionBlock:^(UIImage *image, NSDictionary *metadata)

directly in the particular method. This way you won't drain the device memory.