How to delay load specific content of UICollectionViewCell

Question

I implemented a calendar view with UICollectionView, when scrolling the calendar view very fast, it's not smooth. So I'm thinking whether I can load static content of each cell firstly, and then refresh once specific content has been loaded. So how to delay loading specific contents of each UICollectionViewCell

Specifically, in below function, I'll construct each UICollectionViewCell and return it. Now I just want to construct static contents (such as the date), and delay loading specific contents (such as the background color, if I have an event this day, I'll change the background of this cell), so where should I load specific contents, and how to only refresh showing cell

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    UICollectionViewCell *cell = [self.collectionView dequeueReusableCellWithReuseIdentifier:UICollectionViewCellIdentifier
                                                                                     forIndexPath:indexPath];

    NSDate *date = [self dateAtIndexPath:indexPath];

    cell.dateLabel.text = [date description];

    // This is the part I want to delay, since it's cost.
    if (dataModel.hasEventAtDate(date)) {
        cell.dateLabel.backgroundColor = [UIColor blue];
    }
    return cell;
}

Can you show more what do you want to delay load? For the delay, you can use dispatch_after — tuledev, Aug 26 '15 at 09:59
thanks, i just updated my question, please check out the latest version — Yuwen Yan, Aug 26 '15 at 10:08
You can try to use dispatch_after. But I think it still isn't smooth. http://stackoverflow.com/questions/4139219/how-do-you-trigger-a-block-after-a-delay-like-performselectorwithobjectafter — tuledev, Aug 26 '15 at 10:21

score 0 · Answer 1 · answered Aug 26 '15 at 10:36

You may need have an instance variable to track if cells need to update:

Boolean cellNeedsUpdate = NO

In cellForItemAtIndexPath, check if you need to fully update the cells:

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
    if (cellNeedsUpdate) {
        // fully update the cell
    } else {
        // do partial update
    }
}

Track end scrolling of the collectionView, then reload the collectionView:

- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView {
    cellNeesUpdate = !cellNeedsUpdate;
    [collectionView reloadData];
}

How to delay load specific content of UICollectionViewCell

1 Answers1