Jure Jure - 3 days ago 5
iOS Question

UITableViewCell height resize when image is downloaded

I'm using

UIImageView+AFNetworking
category for async image loading. Everything works fine, but I've tried a couple of things and wasn't successful when resizing the cell's height according to the downloaded image. I want the image to fit to the width of the cell but resize in height, but I don't know how to accomplish that. I've tried reloading the row where the image was downloaded but that just causes the
cellForRowAtIndexPath
to fire again and set everything again, etc. Almost a recursion.

I'm calculating the new image size difference and storing that in
NSMutableArray
and then reloading the row in the success block in UIImageView's
setImageWithURLRequest:placeholderImage:success:
.

I get the correct height for a couple of rows in
heightForRowAtIndexPath
but then, the table starts acting weird and everything is overlaying, etc.

Any ideas?

Thanks!

EDIT

I eventually used Ezeki's answer. I also wrote a post on the topic and made a sample app that uses this technique.

Check it out on here.

Answer

You need to store downloaded image in the memory or on the disk, so next time when you will try to get image from this URL you will received from cache.

So if you do that than you will have to do something like this:

[tableView beginUpdates];

[tableView reloadRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationFade];

[tableView endUpdates];

And you should return new cell's height in this method of table view data source:

- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath

I would recomend you to use SDWebImage library instead of AFNetworking because it can cache your images to memcache and disk for you and it is very easy to use. So if you decide to use it, your code of download images will be looking like this:

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {

    ...

    [cell.imageView setImageWithURL:[NSURL URLWithString:@"http://www.domain.com/path/to/image.jpg"]
           placeholderImage:[UIImage imageNamed:@"placeholder.png"]
                    success:^(UIImage *image, BOOL cached) {

                        // save height of an image to some cache
                        [self.heightsCache setObject:[NSNumber numberWithFloat:imHeight] 
                                              forKey:urlKey];

                        [tableView beginUpdates];
                        [tableView reloadRowsAtIndexPaths:@[indexPath]
                                         withRowAnimation:UITableViewRowAnimationFade];
                        [tableView endUpdates];
                    }
                    failure:^(NSError *error) {... failure code here ...}];

}

- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath {
    // try to get image height from your own heights cache
    // if its is not there return default one
    CGFloat height = [[self.heightsCache objectForKey:urlKeyFromModelsArrayForThisCell] floatValue];
    ...
    return newHeight;
}
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