Question

So I have a UITableViewCell subclass that needs to know whether the UITableView is currently scrolling or not to update the UI. So I had a property pointing to the UITableView in the subclass and I have the following method delegate for the UIScrollView delegate:

- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
    CGFloat scrollOffset = scrollView.contentOffset.y;
    CGFloat contentHeight = scrollView.contentSize.height - kLoadMoreOffset;

    if (scrollOffset >= contentHeight && loadMore && [self.nextPaginationURL_ isNotNull]){
        loadMore = NO;
        [self loadMore];
    }

    self.isScrolling = [NSNumber numberWithInt:1];
}

-(void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate  
{
    if (!decelerate){
        self.isScrolling = [NSNumber numberWithInt:0];
        NSLog(@"FIRING NOTIF END DRAGGING");
         [self showLoadMore];
    }
}

- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
{
     NSLog(@"FIRING NOTIF END DECEL");
    self.isScrolling = [NSNumber numberWithInt:0];
    [self showLoadMore];

}

Is scrolling is essentially a NSNumber to indicate whether the scroll view is scrolling or not. I am passing this to the UITableViewCell to later on be used in the class, to see if the state is scrolling or not. I was planning to use KVO but it is impossible to do that with just a BOOL (or if it’s possible let me know). Is there a more elegant way to do this?

I have an assign property in my UITableViewCell as follows

@property (nonatomic, assign) BOOL isScrolling

and when I am initing my UITableViewCell subclass I am assinging isScrolling with the isScrolling on the UITableView. I guess my biggest concern with this approach is that if I change isScrolling on the UIScrollView delegate, will the isScrolling property on the UITableViewCell subclass also reflect the change?

Answer 1

No it will not do that, you need to notify the visible cells manually about the change. Write a method to do the work for you and just call it from the delegate methods:

- (void)notifyCellsOfScrolling:(BOOL)isScrolling_
{
    // Small optimization, if the state has not changed we don't need to notify.
    if (self.isScrolling == isScrolling_)
        return;

    self.isScrolling = isScrolling_;
    for (UITableViewCell *cell in [self.tableView visibleCells])
        [cell setIsScrolling:isScrolling_];
}

You must also setup the proper state from cellForRowAtIndexPath.