setImage for UIImageView in uitableviewcell lags scrolling in iOS

Question

I have a gallery view of photos that are downloaded from the internet so I used Enormego's EGOImageView. I noticed that when i scrolled down my tableview after the images were in the cache, the scrolling would lag. I immediately found that when the image was retrieved from the hard drive with return [UIImage imageWithContentsOfFile:cachePathForKey(key)]; it was working on the main thread so I added the operation to an NSOperationQueue. This reduced the lag by half but the scrolling still stuttered. After going through the code, I noticed that in the success method

- (void)imageLoaderDidLoad:(NSNotification*)notification {
    if(![[[notification userInfo] objectForKey:@"imageURL"] isEqual:self.imageURL]) return;

    UIImage* anImage = [[notification userInfo] objectForKey:@"image"];
    self.image = anImage;
    [self setNeedsDisplay];

    if([self.delegate respondsToSelector:@selector(imageViewLoadedImage:)]) {
        [self.delegate imageViewLoadedImage:self];
    }
}

commenting out the self.image = anImage; got rid of the lag completely (but obviously I get no image). And as far as I can tell, if I want to alter the UI, it must be done in the main thread. Is there a way to set the image for the EGOImageView without it lagging the scrolling?

Note: the JPGs are around 50kB

Thanks

Answer 1

From what I understand, all the steps required to initiate an asynchronous disk query takes a couple milliseconds on the mainthread, and that is enough time for the scrolling to look like it stutters, so I decided to completely remove hard drive caching for large images and instead create an NSMutableDictionary which holds the UIImage as an object, and the NSURL.absoluteString as the key. This works seamlessly but obviously has the disadvantage of being a memory hog. I checked out the memory usage of some photo-sharing apps and I've been able to get the memory usage for the app to over 100MB so it seems everybody else is doing this.

Answer 2

1. Subclass uitableViewCell and do your own drowing in drawContentView.
2. Resize images in background thread and then present them in cells.

P.S: if the code found on git hub is not good enough for you, try to write your own that suits your problem.