Uitableviewcell Height Resize When Image Is Downloaded

UITableViewCell height resize when image is downloaded

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;
}

Updating cell height after image downloads

Short Answer

• Give enough breathing space to estimatedRowHeight
• Changing a UITableViewCell once returned by dequeueReusableCellWithIdentifier will not work with cached cells
• Trigger a single cell reload with reloadRowsAtIndexPaths
• Manage your cache with Core Data and let NSFetchedResultsController boilerplate code can do all the UI work.

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In Details

No unexpected scroll, only updates images as they come:

1. If the cell being refreshed is at or below the horizon, the UITableView will not scroll
2. if the cell being refreshed is above the top, the UITableView will not scroll
3. the UITableView will only scroll when the cell is in plain sight, and requires more space than available.

Let UITableViewAutomaticDimension do the hard work

You need to tell Cocoa Touch that the cell is stale, so that it will trigger a new dequeueReusableCellWithIdentifier, to which you are going to return a cell with the proper height.

Short of reloading the entire table view or one of its section, and assuming that your indexes are stable, invoke -tableView:reloadRows:at:with: passing the indexPath of the cell that just changed, and a .fade animation.

Code:

override func viewDidLoad() {
    super.viewDidLoad()
    tableView.estimatedRowHeight = 250 // match your tallest cell
    tableView.rowHeight = UITableViewAutomaticDimension
}

Use URLSession. When an image becomes available, fire reloadRows:at:with:

func loadImage(_ url: URL, indexPath: IndexPath) {
    let downloadTask:URLSessionDownloadTask =
        URLSession.shared.downloadTask(with: url, completionHandler: {
        (location: URL?, response: URLResponse?, error: Error?) -> Void in
        if let location = location {
            if let data:Data = try? Data(contentsOf: location) {
                if let image:UIImage = UIImage(data: data) {
                    self.cachedImages[indexPath.row] = image // Save into the cache
                    DispatchQueue.main.async(execute: { () -> Void in
                        self.tableView.beginUpdates()
                        self.tableView.reloadRows(
                            at: [indexPath],
                            with: .fade)
                        self.tableView.endUpdates()
                    })
                }
            }
        }
    })
    downloadTask.resume()
}

Once in the cache, cellForRow merely reads into it from the UI thread:

override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell
{
    let cell = tableView.dequeueReusableCell(withIdentifier: "id") as! CustomCell
    cell.imageView.image = cachedImages[indexPath.row]      // Read from the cache
    return cell
}

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Example: fetch a random set of images from *Wikipedia*

► Find this solution on GitHub and additional details on Swift Recipes.

Dynamic TableViewCell height to fit downloaded image

Storyboard:

• Add a new cell to your table view
• Add a new image view to the cell
• Optionally set a placeholder image for the image view
• Make cell's constraints describe its height unambiguously

Be sure to leave Row Height of the cell set to Default

Code:

Make the table view to self-size cells:

var tableview: UITableView {
    didSet {
        tableView.rowHeight = UITableViewAutomaticDimension
        tableView.estimatedRowHeight = 44
    }
}

At runtime, start loading the image asynchronously as soon as possible.

When downloaded, load the image to the image view and execute:

tableView.beginUpdates()
tableView.endUpdates()

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