Question

Is there any message I can override called when a Table Cell goes away (on scrolling the table)?

I think it should be something like dealoc.

I’m asking this because I have below situation:
I have a table with many cells (100+) and each of this cell contains a ImageView. For loading the image (from a URL) I’m using NSOperationQueue/NSInvocationOperation. The problem appears when user is scrolling the table before the image is completely loaded: because I’m reusing the cells the image is displayed in wrong cell.

To avoid this I’m thinking to use “cancelAllOperations” of NSOperationQueue object when the cell goes away.

Note: I’ve tried but is not working if I call this message on “prepareForReuse”.

Answer 1

If there were, it would be in the UITableViewDelegate class reference: http://developer.apple.com/iphone/library/documentation/UIKit/Reference/UITableViewDelegate_Protocol/Reference/Reference.html#//apple_ref/occ/intf/UITableViewDelegate

The only thing they have is willDisplayCell which lets you do last minute adjustments BEFORE the cell appears. They don’t have anything for when it disappears, but you could probably figure that out since there are only a certain number of cells on the screen at a time for a given cell height.

So if one is appearing and for a cell height of 80 for instance (in portrait mode so 480px screen height), then you can say that the one 6 cells away is about to disappear (6 cells * 80 pixels = 480). There are a couple other things to consider like which way you are scrolling, but you get the general idea.

Example Code: You should also look at lazy table loading via Apple’s sample code http://developer.apple.com/iphone/library/samplecode/LazyTableImages/Introduction/Intro.html