CODEWITHSUNDEEP
iphoneiosipaduitableviewmemory-management
Luffen
Luffen

Reputation: 403

Memory Handling for thumbnail images in UITableViewCells

Short Explanation

Currently I have a UITableView which contains cells of videos from a website. In addition each cell (which represents a video) has a specific thumbnail image. These images are downloaded asynchrounously using NSURLConnection (so I do not have to worry about threading myself). When these image objects have downloaded they simply notify the UITableView to refresh the cell it belongs to.

My Problem

As standard there will be fetched 10 new videos to the UITableView each call. This means that the user is allowed to push a cell at the bottom of the UITableView to request 10 new videos and so forth. The problem here is that there will quickly be a whole lot of memory usage because data for all thumbnail images (in the UITableView) will still exists no matter what.

Is there a smart way in which you can de-allocate image objects that aren't currently in the view?

Also, the UITableView simply renders all its cells directly from an array I have of all video objects ever fetched from the website. This means there is no limits as to how many times the user can request new videos, making this array bigger and bigger all the time. Is it correct to keep these kind of arrays in memory all the time? Or should you instead delete the ones which goes out of the view and request them again later on?

Thank you in advance

Upvotes: 2

Views: 656

Answers (2)

Max
Max

Reputation: 989

If you create your own class VideoTableViewCell as a subclass of UITableViewCell and you give your cell a property for an image this image will be released as soon as the cell goes off the screen. The cell and the image will be recreated as soon as the Cell come back on the view.

For the videos I would store all downloaded video files in the documents folder and store there url in an array. If a cell comes visible or is clicked simply load the file from the hard drive.

Upvotes: 0

isaac
isaac

Reputation: 4897

If you're using the standard method approach of queuing and de-queuing cells in your tableview, then you really should only be using a handful of cell views (and their related thumbnails) - eg, the total number of cell views allocated should never be more than the maximum number viewable on screen, and by extension, the number of allocated/references to thumbnail images should not exceed the total number of cells. Each time you present a row representing a new movie, the imageview is as likely reused as it is new.

What you want to consider is that your data array (an array of your downloaded clips, with potentially unlimited objects therein) is completely discrete from your tableview's array of cells, which is going to be a relatively small number.

My advice would be to conceive a download cache of images. Basically, as your thumbnails are downloaded, assign each a unique string id, and write the actual image file out to disk. Assign the unique ID string to your model object. When your tableview prepares to present an image, locate the image for the cell using the id string, load the image from disk, and populate the image view. As long as you're not retaining the image, the image should be released when the cell presenting it goes off-screen. You can additionally empty the cache of loaded images under low memory conditions.

Upvotes: 1

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