UIImage save to PNG cause memory leak

Question

I'd like to save UIImage in NSArray to local as PNG. However, When I used UIImagePNGRepresentation in a for-loop, memory grew up greatly even though there is already a @autoreleasepool.

for (int i = 0; i < array.count; i++) {

    @autoreleasepool {
        NSDictionary *src = array[i];

        NSString *localPath = [SPLDPath stringByAppendingPathComponent:@"realImg"];
        NSFileManager *file = [NSFileManager defaultManager];
        if (![file fileExistsAtPath:localPath]) {
            [file createDirectoryAtPath:localPath withIntermediateDirectories:NO attributes:nil error:nil];
        }

        NSString *screenShotImg = [localPath stringByAppendingPathComponent:[NSString stringWithFormat:@"ScreenShot_%d.png", i]];
        NSData *PNGData = UIImagePNGRepresentation(src[@"image"]);
        [PNGData writeToFile:screenShotImg atomically:YES];
    }
}

So I tried to convert UIImage to CGImageRef and use ImageIO framework to save image. Then using CGImageRelease() to release memory in each loop.

-(void)saveImage:(CGImageRef)image directory:(NSString*)directory filename:(NSString*)filename  {
@autoreleasepool {
    CFURLRef url = (__bridge CFURLRef)[NSURL fileURLWithPath:[NSString stringWithFormat:@"%@/%@", directory, filename]];
    CGImageDestinationRef destination = CGImageDestinationCreateWithURL(url, kUTTypePNG, 1, NULL);
    CGImageDestinationAddImage(destination, image, nil);

    if (!CGImageDestinationFinalize(destination))
        NSLog(@"ERROR saving: %@", url);

    CFRelease(destination);
    CGImageRelease(image);
}

}

for (int i = 0; i < array.count; i++) {

   NSDictionary *src = array[i];

   NSString *localPath = [SPLDPath stringByAppendingPathComponent:@"realImg"];
        NSFileManager *file = [NSFileManager defaultManager];
   if (![file fileExistsAtPath:localPath]) {
       [file createDirectoryAtPath:localPath withIntermediateDirectories:NO attributes:nil error:nil];
   }
   NSString *fileName = [NSString stringWithFormat: @"ScreenShot_%d.png", i];

   CGImageRef cgRef=[src[@"image"] CGImage];
   [self saveImage:(cgRef) directory:localPath filename:fileName];

} enter image description here The memory was decreased, however, a new issue happened. My app was crashed because of over-released memory. Because the UIImage was released by CGImageRelease(), but ARC also tried to send a delloc message to the zombie object before the app end. How can I free the CGImageRef but not collide with ARC?

Answer 1

Do not invoke CGImageRelease() on the CGImage property, since your code does not hold a incr ref to that object. You would only release in this case if your code explicitly incremented the ref someplace.