Lazy load images for UITableViewCells from NSDocumentDirectory?

Question

Hey.

I have a tableView in my app that I load in images to from the NSDocumentDirectory. It works, but when scrolling up and down, the app seems to freeze a bit. I know that this is because of the images getting loaded in, and not getting cached, but I don't know how I can load them in later, after they've been created.

The images are .png-s, 10kB to 50kB big and 300*127 in size.

I am currently loading them in with this code:

imagesPath = [NSString stringWithFormat:@"%@/images/", [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0]];
if ([fileManager fileExistsAtPath:[imagesPath stringByAppendingPathComponent:[NSString stringWithFormat:@"/%d.png", rowID]]]) {
    UIImage *image = [[UIImage alloc] initWithContentsOfFile:[imagesPath stringByAppendingPathComponent:[NSString stringWithFormat:@"/%d.png", rowID]]];
    // If image contains anything, set cellImage to image. If image is empty, use default, noimage.png.
    if (image != nil){
        // If image != nil, set cellImage to that image
        cell.cellImage.image = image;
    }

    [image release];
    image = nil;
}

Answer 1

Take a look at the SDWebImage repository. It provides everything to perform asynchronous image loading.

Update

I just noticed that there is some typos in the README, so downloading a local file may not work as expected.

Here is some sample code. The view controller has an UIImageView outlet and wants to load the image.jpg file. It implements the SDWebImageManagerDelegate protocol:

- (IBAction)loadImage:(id)sender {
    SDWebImageManager *manager = [SDWebImageManager sharedManager];

    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    NSString *destPath = [documentsDirectory stringByAppendingPathComponent:@"image.jpg"];
    NSURL *url = [NSURL fileURLWithPath:destPath];
    UIImage *cachedImage = [manager imageWithURL:url];
    if (cachedImage)
    {
        imageView.image = cachedImage;
    }
    else
    {
        // Start an async download
        [manager downloadWithURL:url delegate:self];
    }    
}

- (void)webImageManager:(SDWebImageManager *)imageManager didFinishWithImage:(UIImage *)image
{
    imageView.image = image;
}