Memory pressure due to download and saving of images - ios

Question

Fortunately I know where my memory pressure issue is coming from, and I have tried a number of techniques such as wrapping a block in an #autorelease block and setting objects to nil but still no success.
Sorry for dumping too much code here, I tried to cut it down to the essentials. Here is the code for downloading and saving images:
NSMuttableArray *photosDownOps = [NSMuttableArray array];
NSURL *URL = [...];
NSURLRequest *request = [...];
AFHTTPRequestOperation *op = [[AFHTTPRequestOperation alloc] initWithRequest:request];
op.responseSerializer = [AFImageResponseSerializer serializer];
[op setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
dispatch_queue_t amBgSyncQueue = dispatch_queue_create("writetoFileThread", NULL);
dispatch_async(amBgSyncQueue, ^{
[self savePhotoToFile:(UIImage *)responseObject usingFileName:photo.id];
});
} failure:^(AFHTTPRequestOperation *operation, NSError *error) {
if ([error code] != NSURLErrorCancelled)
NSLog(#"Error occured downloading photos: %#", error);
}];
[photosDownOps addObject:op];
NSArray *photosDownloadOperations = [AFURLConnectionOperation batchOfRequestOperations:photosDownloadOperatons
progressBlock:^(NSUInteger nof, NSUInteger tno) {
} completionBlock:^(NSArray *operations) {
NSLog(#"all photo downloads completed");
}];
[self.photosDownloadQueue addOperations:photosDownloadOperations waitUntilFinished:NO];
+ (void) savePhotoToFile:(UIImage *)imageToSave usingFileName:(NSNumber *)photoID{
#autoreleasepool {
NSData * binaryImageData = UIImageJPEGRepresentation(imageToSave, 0.6);
NSString *filePath = [Utilities fullPathForPhoto:photoID];
[binaryImageData writeToFile:filePath atomically:YES];
binaryImageData = nil;
imageToSave = nil;
}
}
This situation though only happens with iPhone 4s devices that I have tested on, it does not happen on iPhone 5 models.

Answer 1

I managed to solve this by extending NSOperation and within the main block immediately after I receive the data I write it out to file:
- (void)main{
#autoreleasepool {
//...
NSData *imageData = [[NSData alloc] initWithContentsOfURL:imageUrl];
if (imageData) {
NSError *error = nil;
[imageData writeToFile:imageSavePath options:NSDataWritingAtomic error:&error];
}
//...
}
}
This NSOperation object was then added a NSOperationQueue I already had.

Answer 2

Try to create your own class to download image using NSUrlConnection and in the delegate method append that data to your file just see the below code
-(void)connection:(NSURLConnection*)connection didReceiveData:(NSData*)data {
NSFileHandle *fileHandle = [NSFileHandle fileHandleForWritingAtPath:aPath];
[fileHandle seekToEndOfFile];
[fileHandle writeData:data];
[fileHandle closeFile];
}
This will help you in memory management as all the data which is download is not need to cache .