Question

Is my - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath delegate I have the following code:

if ([movie isDownloaded])
    cell.detailTextLabel.text = movie.duration;
else
{
    cell.detailTextLabel.text = @"";

    [movie downloadInQueue:self.downloadQueue completion:^(BOOL success) {

        UITableViewCell *updateCell = [tblView cellForRowAtIndexPath:indexPath];            
        if (updateCell)
        {
            updateCell.detailTextLabel.text = movie.duration;
            [updateCell setNeedsLayout];
        }
    }];
}

Which calls into Movie.m and runs this code:

- (void)downloadInQueue:(NSOperationQueue *)queue completion:(void (^)(BOOL success))completion
{
    if (!self.isDownloading)
    {
        self.downloading = YES;

        [queue addOperationWithBlock:^{
            BOOL success = NO;

            AVPlayerItem *playerItem = [AVPlayerItem playerItemWithURL:self.fileURL];
            CMTime timeduration = playerItem.duration;
            float seconds = CMTimeGetSeconds(timeduration);
            self.duration = [self timeFormatted:seconds];

            self.downloading = NO;
            self.downloaded = YES;
            success = YES;

            [[NSOperationQueue mainQueue] addOperationWithBlock:^{
                completion(success);
            }];
        }];
    }
}

When my cells become not visible, I want to cancel the NSOperation in the Movie object if it hasn’t been run yet (remove it from the queue). I know I can subclass UITableViewCell and do something like this:

- (void)willMoveToWindow:(UIWindow *)newWindow
{
    [super willMoveToWindow:newWindow];

    if (newWindow==nil) {
            // Cell is no longer in window so cancel from queue
    }
}

Question… how can I cancel my Movie NSOperation from within the UITableViewCell delegate call? With a delegate or NSNotification of some kind? I need to know the indexPath of the cell to get the correct Movie object out of my array and cancel the operation.

Answer 1

As of iOS 6 you can use the tableView:didEndDisplayingCell:forRowAtIndexPath: method of the UITableView Delegate protocol. This gets called when the cell is removed from the table view (which happens when it is no longer visible).

- (void)tableView:(UITableView *)tableView didEndDisplayingCell:(UITableViewCell *)cell forRowAtIndexPath:(NSIndexPath *)indexPath {
    // Cancel operation here for cell at indexPath
}