I have a gallery in my app utilizing a UICollectionView. The cells are approximately 70,70 size. I am using ALAssets from the ALAssetLibrary in the gallery which I have stored in a list.
I am using the usual pattern for populating the cells:
-(UICollectionViewCell*)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
mycell = [collectionView dequeueReusableCellWithReuseIdentifier:cellIdentifier forIndexPath:indexPath];
mycell.imageView.image = [[UIImage imageWithCGImage:[alassetList objectAtIndex:indexpath.row] thumbnail]];
return mycell;
}
My gallery is scrolling choppy. I don't understand why this is. I've tried adding a NSCache to cache the thumbnail images (thinking maybe creating the images was expensive) but this did not help for the performance.
I would expect the UI to be as buttery as the stock app.
I am now suspecting it may be something in the UICollectionViewCell prepareForReuse that may be holding up the dequeueReusableCellWithReuseIdentifier method but using instruments I was not able to find this.
Any other thing that may be be causing this? Is there a "faster" way to prepare the UICollectionViewCell or to dequeue them in a faster fashion?
So anybody having scrolling issues should do this
add these 2 lines after your dequeue
cell.layer.shouldRasterize = YES;
cell.layer.rasterizationScale = [UIScreen mainScreen].scale;
I would assume the "choppyness" is coming from the UIImage allocation, not anything with the dequeueReusableCellWithReuseIdentifier method. I'd try doing the image allocation on a background thread and see if that makes things a little more buttery.
-(UICollectionViewCell*)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
mycell = [collectionView dequeueReusableCellWithReuseIdentifier:cellIdentifier forIndexPath:indexPath];
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^(void) {
// Load image on a non-ui-blocking thread
UIImage *image = [[UIImage imageWithCGImage:[alassetList objectAtIndex:indexpath.row] thumbnail]];
dispatch_sync(dispatch_get_main_queue(), ^(void) {
// Assign image back on the main thread
mycell.imageView.image = image;
});
});
return mycell;
}
More details can be found here: https://developer.apple.com/library/ios/documentation/Cocoa/Conceptual/Multithreading/Introduction/Introduction.html
Load your images using NSURLConnection's sendAsynchronousRequest:queue:completionHandler:
NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:urlString]];
[NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse *response, NSData *data, NSError *error) {
[cell.imageView setImage:[UIImage imageWithData:data]];
}];
Tick on clip subviews and opaque in attributes inspector and tick off paging enabled.
If anyone is using PhImageManager, turning off synchronous solved the problem. (deliveryMode = .FastFormat can also give additional performance enhancement, but the tradeoff is the thumbnail will be of lower quality)
let option = PHImageRequestOptions()
option.deliveryMode = .Opportunistic
option.synchronous = false
PHImageManager().requestImageForAsset(phAsset, targetSize: CGSizeMake(2048, 2048), contentMode: .AspectFit, options: option, resultHandler: { (image, objects) in
self.imageView.image = image!
})
I had issues with UICollectionView scrolling.
What worked (almost) like a charm for me: I populated the cells with png thumbnails 90x90. I say almost because the first complete scroll is not so smooth, but never crashed anymore...
In my case, the cell size is 90x90.
I had many original png sizes before, and it was very choppy when png original size was greater than ~1000x1000 (many crashes on first scroll).
So I select 90x90 (or the like) on the UICollectionView and display the original pngs (no matter the size). Hope this helps others.
Related
I have made a custom Tableview which has an image view and some labels that takes values from API.
It's a custom table in which images and labels recieve data from API related to real estate .
When my custom table loads, values start coming from API.
The actual issue ocurr in image view . I have set a local image in an image view , when the data coming from API has no image than it should show local image otherwise data should show its original image submitted by customer in the forms.
Now when data start coming from API first in image view it shows local image than when images start coming from API it start showing that but when we scroll down in image view it shows same images in image view and repeats many times and we cannot identify that which is original image.
I can provide the code if anyone sent me his email , he can get all the senario of work.
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
static NSString *cellIdentifier=#"Cell";
CustomTableViewCell *cell=[tableView dequeueReusableCellWithIdentifier:cellIdentifier forIndexPath:indexPath];
StringData* cust = [_Title objectAtIndex:indexPath.row];
cell.Title.text = cust.title1;
cell.area.text=cust.Area;
cell.city.text=cust.City;
cell.phone.text=cust.phoneno;
cell.price.text=cust.Price;
cell.location1.text=cust.location;
cell.name1.text=cust.dealer_name;
cell.email1.text=cust.dealer_email;
cell.type1.text=cust.property_type;
cell.status1.text=cust.status;
cell.room1.text=cust.rooms;
cell.washrooms.text=cust.bath;
cell.floor1.text=cust.floors;
cell.imagetext.text = cust.images;
tii=cell.Title.text;
NSLog(#"Tittttttle is %#",tii);
NSURL *url = [NSURL URLWithString:cust.images];
NSURLSessionTask *task = [[NSURLSession sharedSession] dataTaskWithURL:url completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
if (data) {
UIImage *image = [UIImage imageWithData:data];
if (image) {
dispatch_async(dispatch_get_main_queue(), ^{
cell.images1.image = image;
});
}
}
}];
[task resume];
return cell;
}
It seems you don't store an image into local application memory. You tried to load image on every time when cell is appear. So you download image every time.
Best Solution:
You need to store image local memory using SDWebImage.
Objective-C:
#import <SDWebImage/UIImageView+WebCache.h>
...
[imageView sd_setImageWithURL:[NSURL URLWithString:#"IMAGE_URL"]
placeholderImage:[UIImage imageNamed:#"placeholder.png"]];
Swift:
import SDWebImage
imageView.sd_setImage(with: URL(string: "IMAGE_URL"), placeholderImage: UIImage(named: "placeholder.png"))
If you are loading an image for the first time, then it will download and store an image into local memory. So from second times, it will load from local itself.
Well, its because your cell is getting re-used and the previous image is being displayed. You can override prepareForReuse() method of your tableviewcell subclass or consider setting placeholder for the url image using SDWebImage
Edit: Explaination
You are downloading your image asyc and setting it to your imageview of your tableviewcell, what is happening here is while your next image is being downloaded, before that your cell is re-used and displays previous image.
This question already has answers here:
Async image loading from url inside a UITableView cell - image changes to wrong image while scrolling
(13 answers)
Closed 9 years ago.
Im using a asynchronous block (Grand central dispatch) to load my cell images. However if you scroll fast they still appear but very fast until it has loaded the correct one. Im sure this is a common problem but I can not seem to find a away around it.
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = #"Cell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];
// Load the image with an GCD block executed in another thread
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:[[[appDelegate offersFeeds] objectAtIndex:indexPath.row] imageurl]]];
dispatch_async(dispatch_get_main_queue(), ^{
UIImage *offersImage = [UIImage imageWithData:data];
cell.imageView.image = offersImage;
});
});
cell.textLabel.text = [[[appDelegate offersFeeds] objectAtIndex:indexPath.row] title];
cell.detailTextLabel.text = [[[appDelegate offersFeeds] objectAtIndex:indexPath.row] subtitle];
return cell;
}
At the very least, you probably want to remove the image from the cell (in case it is a re-used cell) before your dispatch_async:
cell.imageView.image = [UIImage imageNamed:#"placeholder.png"];
Or
cell.imageView.image = nil;
You also want to make sure that the cell in question is still on screen before updating (by using the UITableView method, cellForRowAtIndexPath: which returns nil if the cell for that row is no longer visible, not to be confused with the UITableViewDataDelegate method tableView:cellForRowAtIndexPath:), e.g.:
static NSString *CellIdentifier = #"Cell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];
cell.imageView.image = [UIImage imageNamed:#"placeholder.png"];
// Load the image with an GCD block executed in another thread
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:[[[appDelegate offersFeeds] objectAtIndex:indexPath.row] imageurl]]];
if (data) {
UIImage *offersImage = [UIImage imageWithData:data];
if (offersImage) {
dispatch_async(dispatch_get_main_queue(), ^{
UITableViewCell *updateCell = [tableView cellForRowAtIndexPath:indexPath];
if (updateCell) {
updateCell.imageView.image = offersImage;
}
});
}
}
});
cell.textLabel.text = [[[appDelegate offersFeeds] objectAtIndex:indexPath.row] title];
cell.detailTextLabel.text = [[[appDelegate offersFeeds] objectAtIndex:indexPath.row] subtitle];
return cell;
Frankly, you should also be using a cache to avoid re-retrieving images unnecessarily (e.g. you scroll down a bit and scroll back up, you don't want to issue network requests for those prior cells' images). Even better, you should use one of the UIImageView categories out there (such as the one included in SDWebImage or AFNetworking). That achieves the asynchronous image loading, but also gracefully handles cacheing (don't reretrieve an image you just retrieved a few seconds ago), cancelation of images that haven't happened yet (e.g. if user quickly scrolls to row 100, you probably don't want to wait for the first 99 to retrieve before showing the user the image for the 100th row).
This is a problem with async image loading...
Let's say you have 5 visible rows at any given time.
If you are scrolling fast, and you scroll down for instance 10 rows, the tableView:cellForRowAtIndexPath will be called 10 times. The thing is that these calls are faster than the images are returned, and you have the 10 pending images from different URL-s.
When the images finally come back from the server, they will be returned on those cells that you put in the async loader. Since you are reusing only 5 cells, some of these images will be displayed twice on each cell, as they are downloaded from the server, and that is why you see flickering. Also, remember to call
cell.imageView.image = nil
before calling the async downloading method, as the previous image from the reused cell will remain and also cause a flickering effect when the new image is assigned.
The way around this is to store the latest URL of the image you have to display on each cell, and then when the image comes back from the server check that URL with the one you have in your request. If it is not the same, cache that image for later.
For caching requests, check out NSURLRequest and NSURLConnection classes.
I strongly suggest that you use AFNetworking for any server communication though.
Good luck!
The reason of your flicker is that your start the download for several images during the scrolling, every time you a cell is displayed on screen a new request is performed and it's possible that the old requests are not completed, every tile a request completes the image is set on the cell, so it's if you scroll fast you use let's say a cell 3 times = 3 requests that will be fired = 3 images will be set on that cell = flicker.
I had the same issue and here is my approach:
Create a custom cell with all the required views. Each cells has it's own download operation. In the cell's -prepareForReuse method. I would make the image nil and cancel the request.
In this way for each cell I have only one request operation = one image = no flicker.
Even using AFNetworking you can have the same issue if you won't cancel the image download.
The issue is that you download the image on the main thread. Dispatch a background queue for that:
dispatch_queue_t myQueue = dispatch_queue_create("myQueue", NULL);
// execute a task on that queue asynchronously
dispatch_async(myQueue, ^{
NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:[[[appDelegate offersFeeds] objectAtIndex:indexPath.row] imageurl]]];
//UI updates should remain on the main thread
UIImage *offersImage = [UIImage imageWithData:data];
dispatch_async(dispatch_get_main_queue(), ^{
UIImage *offersImage = [UIImage imageWithData:data];
cell.imageView.image = offersImage;
});
});
I have a CollectionView which displays some info about users. One of these items is a user avatar (100x100 png), which is loaded from our webserver. The problems is that it seems to me the view reloads the cells when they have gone outside the screen region. Every time I scroll the page it lags for a bit when the cells that were entirely outside the screen region enter the screen. It's not a really big problem on wifi, but on 3g this is really slow, plus it consumes bandwidth. Overall, it's just bad to handle data like this for my app. I want to load the data once and display it, and not have hundreds of webrequests when the user scrolls the page. Is there any way to load the cells once, and leave them like that until I update them manually? I don't do any updating yet, this is my current code:
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {
return numContacts;
}
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{
UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:#"Cell" forIndexPath:indexPath];
UILabel *contactName = (UILabel *)[cell viewWithTag:1];
char *text = contactArray[indexPath.row].name;
contactName.text = [NSString stringWithCString:text encoding:NSASCIIStringEncoding];
NSData * presence = [NSData dataWithContentsOfFile:[[NSBundle mainBundle] pathForResource:#"offline" ofType:#"png"]];
UIImageView *presenceView = (UIImageView *)[cell viewWithTag:2];
presenceView.image = [UIImage imageWithData: presence];
NSURL *url = [NSURL URLWithString:[NSString stringWithFormat:#"myWebServer",text]];
NSData * avatar = [[NSData alloc] initWithContentsOfURL:url];
UIImageView *avatarView = (UIImageView *)[cell viewWithTag:3];
avatarView.image = [UIImage imageWithData: avatar];
NSData *placeholder = [NSData dataWithContentsOfFile:[[NSBundle mainBundle] pathForResource:#"avatar_unknown" ofType:#"png"]];
[avatarView setImageWithURLRequest:[NSURLRequest requestWithURL:url] placeholderImage:[UIImage imageWithData:placeholder] success:nil failure:nil];
return cell;
}
You are loading the image data in the main queue, so you are blocking it, and thus the interface freezes.
Take a look at the answer to this question: how to send Asynchronous URL Request?
I think instead you should attempt to make one asynchronous service call when your View Controller is loaded to retrieve the data and store it (ex. in an NSMutableArray), because obviously making a service call everytime a cell is loaded is a poor solution. You could even just adjust your Contact custom object (I'm assuming you've created one to store relevant contact info) to include an image property to store the avatar Image. You can't 'load all the cells' because they're reloaded as they appear on the screen.
I rewrote part of the code so I can retrieve all the images at the start, and just display them when my view loads. This solved both problems.
I have this simple UITableView and each cell has an image corresponding to it. All I'm doing is displaying a title for the image and the image itself in each cell. Here is my cellForRowAtIndexPath:
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
// this is where the data for each cell is
NSDictionary *dataForThisCell = cachedData.posts[indexPath.row][#"data"];
// this creates a new cell or grabs a recycled one, I put NSLogs in the if statement to make sure they are being recycled, they are.
post *cell = (post *) [self.tableView dequeueReusableCellWithIdentifier:#"postWithImage"];
if (cell == nil) {
cell = [[[NSBundle mainBundle]loadNibNamed:#"postWithImage" owner:self options:nil]objectAtIndex:0];
[cell styleCell];
}
// if this cell has an image we need to stick it in the cell
NSString *lowerCaseURL = [dataForThisCell[#"url"] lowercaseString];
if([lowerCaseURL hasSuffix: #"gif"] || [lowerCaseURL hasSuffix: #"bmp"] || [lowerCaseURL hasSuffix: #"jpg"] || [lowerCaseURL hasSuffix: #"png"] || [lowerCaseURL hasSuffix: #"jpeg"]) {
// if this cell doesnt have an UIImageView, add one to it. Cells are recycled so this only runs several times
if(cell.preview == nil) {
cell.preview = [[UIImageView alloc] init];
[cell.contentView addSubview: cell.preview];
}
// self.images is an NSMutableDictionary that stores the width and height of images corresponding to cells.
// if we dont know the width and height for this cell's image yet then we need to know now to store it
// once the image downloads, and then cause our table to reload so that heightForRowAtIndexPath
// resizes this cell correctly
Boolean shouldReloadData = self.images[dataForThisCell[#"name"]] == nil ? YES : NO;
// download image
[cell.preview cancelImageRequestOperation];
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString: dataForThisCell[#"url"]]];
[request addValue:#"image/*" forHTTPHeaderField:#"Accept"];
[cell.preview setImageWithURLRequest: request
placeholderImage: [UIImage imageNamed:#"thumbnailLoading.png"]
success: ^(NSURLRequest *request, NSHTTPURLResponse *response, UIImage *image) {
// if we indicated earlier that we didnt know the dimensions of this image until
// just now after its been downloaded, then store the image dimensions in self.images
// and tell the table to reload so that heightForRowAtIndexPath
// resizes this cell correctly
if(shouldReloadData) {
NSInteger imageWidth = image.size.width;
NSInteger imageHeight = image.size.height;
if(imageWidth > [ColumnController columnWidth]) {
float ratio = [ColumnController columnWidth] / imageWidth;
imageWidth = ratio * imageWidth;
imageHeight = ratio* imageHeight;
}
if(imageHeight > 1024) {
float ratio = 1024 / imageHeight;
imageHeight = ratio * imageHeight;
imageWidth = ratio* imageWidth;
}
self.images[dataForThisCell[#"name"]] = #{ #"width": #(imageWidth), #"height": #(imageHeight), #"titleHeight": #([post heightOfGivenText: dataForThisCell[#"title"]]) };
[self.tableView reloadData];
// otherwise we alreaady knew the dimensions of this image so we can assume
// that heightForRowAtIndexPath has already calculated the correct height
// for this cell
}else{
// assign the image we downloaded to the UIImageView within the cell
cell.preview.image = image;
// position the image
NSInteger width = [self.images[dataForThisCell[#"name"]][#"width"] integerValue];
NSInteger height = [self.images[dataForThisCell[#"name"]][#"height"] integerValue];
cell.preview.frame = CGRectMake( ([ColumnController columnWidth] - width)/2 , [self.images[dataForThisCell[#"name"]][#"titleHeight"] integerValue] + 10, width, height);
}
}
failure: ^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error) {}];
}
// set title of the cell
cell.title.text = [NSString stringWithFormat: #"%#\n\n\n\n\n", dataForThisCell[#"title"]];
`enter code here`// ask for a restyle
[cell setNeedsLayout];
// returns my customized cell
return cell;
}
What happens is that everything works exactly how I want it to, however once I scroll down past around 100 cells or so the background of my app goes black for a few seconds and then I see my homescreen (I've seen some people call this the HSOD - home screen of death). Sometimes in the console in xcode I see memory warnings before a crash and sometimes I do not.
I know for a fact that whatever the problem is, it has to do with putting images into the cells. If I comment out just this line:
cell.preview.image = image;
Then everything works fine and it doesn't crash any more (but then of course the images are not being displayed in the cells).
The cells are being reused and I know that's working, for good measure I set the UIImageView's image property to nil:
- (void) prepareForReuse {
[super prepareForReuse];
if(self.preview != nil)
self.preview.image = nil;
}
and in my appDelegate I also define this:
- (void)applicationDidReceiveMemoryWarning:(UIApplication *)application {
[UIImageView clearAFImageCache];
}
Which deletes the image cache but that doesn't fix the problem either (and anyway iOS should clear the image caches upon memory warnings automatically anyway).
I ran analyze on my project and it reports no memory leaks, and here is the profiler showing that, as well as showing the allocations at the time of the crash:
Other than the occasional memory warning in the console which appears about 2/3rds of the time the app crashes, there are no other errors that appear in the console, and I do not hit any breakpoints or exceptions.
All of those allocations are you creating new table view cells each time they're requested, rather than reusing existing ones. Without setting a reuseIdentifier for cells created from UINib, dequeueReusableCellWithIdentifier: will always return `nil.
To fix this, add the following code (as referenced in this question):
[self.tableView registerNib:[UINib nibWithNibName:#"nibname"
bundle:nil]
forCellReuseIdentifier:#"cellIdentifier"];
I've found a solution, albeit not a perfect one:
The AFNetworking library is brilliant and I assume the cause of my problem lies within my own code or my lack of understanding as to how NSCache works.
AFNetworking caches images using Apple's NSCache. NSCache is similar to NSMutableDictionary, but releases objects when memory is spread thin (see more here).
Within UIImageView+AFNetworking.m I located the definition of
+ (AFImageCache *)af_sharedImageCache
And altered it to resemble this:
+ (AFImageCache *)af_sharedImageCache {
static AFImageCache *_af_imageCache = nil;
static dispatch_once_t oncePredicate;
dispatch_once(&oncePredicate, ^{
_af_imageCache = [[AFImageCache alloc] init];
_af_imageCache.countLimit = 35;
});
return _af_imageCache;
}
The important line here is
_af_imageCache.countLimit = 35;
This tells the NSCache object being used in AFNetworking to cache images that it must only cache up to a maximum of 35 things.
For reasons unknown to me, iOS was not automatically purging objects from the cache as it should, and calling removeAllObjects on the cache was not working either. This solution is hardly ideal because it may not utilize the cache to its full potential or may over use the cache, but for the meantime it atleast stops the cache from attempting to store an infinite number of objects.
I have an iOS app that has a UITableView with custom TableViewCells that contain a UIImageView. The image is loaded from a web service, so during the initial load, I display a "loading" image, and then use gcd to dispatch and get the image matching the data for that cell.
When I use a DISPATCH_QUEUE_PRIORITY_HIGH global queue to perform the image fetch, I sporadically get the wrong images loading in the tableview cells. If I use my own custom queue then the correct images get populated into the cells but the tableview performance is awful.
Here is the code...
// See if the icon is in the cache
if([self.photoCache objectForKey:[sample valueForKey:#"api_id"]]){
[[cell sampleIcon]setImage:[self.photoCache objectForKey:[sample valueForKey:#"api_id"]]];
}
else {
NSLog(#"Cache miss");
[cell.sampleIcon setImage:nil];
dispatch_queue_t cacheMissQueue = dispatch_queue_create("cacheMissQueue", NULL);
//dispatch_queue_t cacheMissQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul);
dispatch_async(cacheMissQueue, ^{
if(sample.thumbnailFilename && sample.api_id){
NSData *thumbNailData = [[NSData alloc] initWithContentsOfFile:sample.thumbnailFilename];
UIImage *thumbNailImage = [[UIImage alloc]initWithData:thumbNailData];
if(thumbNailImage){
// Set the cell
dispatch_sync(dispatch_get_main_queue(), ^{
[[cell sampleIcon]setImage:thumbNailImage];
[cell setNeedsLayout];
});
// save it to cache for future references
NSLog(#"DEBUG: Saving to cache %# for sample %#",sample.thumbnailFilename,[sample objectID]);
[self.photoCache setObject:thumbNailImage forKey:sample.api_id];
}
}
});
dispatch_release(cacheMissQueue);
}
Watching the WWDC 2012 session #211 helped a lot and I changed the code from using GCD to NSOperationQueue and it solved the problem.
New code...
[[self imgQueue]addOperationWithBlock:^{
if(sample.thumbnailFilename && sample.api_id){
NSData *thumbNailData = [[NSData alloc] initWithContentsOfFile:sample.thumbnailFilename];
UIImage *thumbNailImage = [[UIImage alloc]initWithData:thumbNailData];
if(thumbNailImage){
// Set the cell
[[NSOperationQueue mainQueue]addOperationWithBlock:^{
[[cell sampleIcon]setImage:thumbNailImage];
[cell setNeedsLayout];
}];
// save it to cache for future references
[self.photoCache setObject:thumbNailImage forKey:sample.api_id];
}
}
}];
When you finally get an image, you need an association between the indexPath of the cell and the image. Since this is on a backgound thread, what I suggest you do is post a nofification using a block to the mainQueue that such and such an image is available. On the main thread only, you ask the tableView for the array of visible cells, and if the cell you have an image for is showing, you can then set the image directly at that time (your on the main thread, you know the cell is there and showing, and its not going to change for this runloop iteration.) If the cell is not showing, no problem, next time that cell comes into scope you will have the image waiting for it. I am doing this now in my app, its been out many months, and its all working well and getting good reviews on responsiveness (just as your app will if you do this!)