How to load images from server to tableView efficiently?

Question

I have a table view with all cells having the UITableViewCellStyleSubtitle, the images of all the cells are got from the server.

However, those images are not changed frequently.

Someone can show me how to improve the user experience? Each time, user scroll down the table, it seems that it goes online to check and download images again.

Or at least, show me some options that are available to achieve the goal.

Thanks,

Answer 1

Try working through the Core Data Tutorial, with a little up-front effort, it will help you very efficiently manage the memory usage in your tableview.

Answer 2

You could try one of the following

• Create an dictionary and cache all the fetched images in it using the image name as the key

• Cache and reuse the entire UITableView cells in tableView:cellForRowAtIndexPath:

• If it is just one image repeating load it one outside tableView:cellForRowAtIndexPath:

• You write that the images change on a monthly basis - you could save the images to disk as they are used and just either check if the images have changed on the back burner or at a given daily interval redownload the images. Brian Chapados reply seems interesting .

Depending on your code there is probably a ton of other ways to improve image loading. Hope that helps...

Answer 3

The Three20 library has an ImageView subclass that accepts a URL to your remote image and uses the excellent TTURLRequest/Caching mechanism to fetch images. It maintains an in-memory and on-disk cache and will only download images if they are not cached or have expired. You can configure the default cache-expiration time or use a value from your HTTP response. If you use the TTTableViewController subclass and the appropriate TTTableItem subclass, you will get the appropriate image downloading behavior for free. However, it is not necessary to use every three component to do what you need. If you're integrating into existing code, you could create your own UITableViewCell subclass that uses a TTImageView instead of the standard UIImageView. Then, in your cell configuration methods, you can set a default placeholder image and a URL to load and it will pretty much take care of the rest. As a performance optimization, you should also implement the UIScrollView delegate methods in your tableview controller to suspend the TTURLRequestQueue during scrolling (take a look at the TTTableViewController to see how this is done).