Question

As soon as the cell is no longer visible on the screen I need to be notified.

UITableView already has a delegate method called tableView:didEndDisplayingCell:forRowAtIndexPath: but this delegate method never gets called. And yes I do have the delegate for my UITableView set.

Any other ways to detect a cell being removed? I need to be able to save the content (inputs) of this cell before it’s being reused by another item.

EDIT:

According to the documentation tableView:didEndDisplayingCell:forRowAtIndexPath: is iOS 6 and higher API. Is there a way to achieve this on iOS 5?

Answer 1

On versions of iOS older than 6.0, the table view doesn’t send the tableView:didEndDisplayingCell:forRowAtIndexPath: message.

If you are using a subclass of UITableViewCell, you can get the same effect on older versions of iOS by overriding didMoveToWindow:

- (void)didMoveToWindow {
    if (self.window == nil) {
        // I have been removed from the table view.
    }
}

You may need to give your cell a (weak or unsafe_unretained) reference back to your table view delegate so you can send the delegate a message.

However, you can’t rely only on didMoveToWindow for all versions of iOS. Before iOS 6, a table view always removed a table view cell as a subview before reusing it, so the cell would always receive didMoveToWindow before being reused. However, starting in iOS 6, a table view can reuse a cell without removing it as a subview. The table view will simply change the cell’s frame to move it to its new location. This means that starting in iOS 6, a cell does not always receive didMoveToWindow before being reused.

So you should implement both didMoveToWindow in your cell subclass, and tableView:didEndDisplayingCell:forRowAtIndexPath: in your delegate, and make sure it works if both are called, or if just one is called.