UICollection view reloadData cause recreate visible cell

Question

When I call reloadData method of UICollectionView it cause all visible cell to blink. I found that reason of this is recreation of all visible cells, while UITableView return visible cell in – tableView:cellForRowAtIndexPath: method after reload data.

So, how can I avoid recreation of visible cells in UICollectionView.

score 19 · Answer 1 · answered May 13 '16 at 19:34

19

You need to reload the visible cells, which will not cause the flash seen during reloadData:

[myCollectionView reloadItemsAtIndexPaths:[myCollectionView indexPathsForVisibleItems]];

answered May 13 '16 at 19:34

Adam W. Dennis

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1

Worked for me . Thanks :) – SSS Nov 20 '18 at 10:52
I still see a momentary flicker, it is much less than with reloadData though. – trapper Jun 14 '19 at 06:23

score 6 · Answer 2 · answered May 17 '14 at 18:51

6

Calling reloadData on either a table or a collection view will recreate (dequeue if possible) all of the (visible) cells and refresh the information about the row / item count and the view content height. So, you will always see a 'blink' because it's animated.

This is by design to inform the user that everything was just updated...

To avoid animation, don't call reloadData. Instead, use visibleCells to get all of the cells that currently exist on the screen and update their contents directly.

answered May 17 '14 at 18:51

Wain

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When I call reloadData for tableView in `tableView:cellForRowAtIndexPath:` I get visible cell with previously loaded data. So, for example, if I have imageView and image don't change I don't update it and thus avoid blinking. But for collection view after reloadData I get entirely new cell - not currently visible cell with data previously loaded. – abagmut May 17 '14 at 19:44
Whether you 'get' a reusable cell is not specific to table or collection view, it's more related to what scrolling you've done or what previous reloads have happened. And you should always reconfigure the cell - how do you know which row it was previously used for... – Wain May 17 '14 at 20:12
I call reloadData when collectionView is not scrolling. It is not necessary to know for which row it was previously used for. Just save image name for image which are currently loaded in cell and if it match after reload (for tableView if cell dataSource not change - it's true) do nothing. – abagmut May 18 '14 at 06:17

score 4 · Answer 3 · edited Jun 15 '20 at 04:23

4

Swift Version:

if let indexPaths = collectionView?.indexPathsForVisibleItems {
    collectionView?.reloadItems(at: indexPaths)
}

edited Jun 15 '20 at 04:23

johndpope

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answered Mar 01 '17 at 08:58

Anh Dung dungi Pham

298
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7

score 4 · Answer 4 · answered Apr 01 '19 at 13:07

You can simply create your own flow layout and set alpha to initial layout attribute, e.g.

class MyFlowLayout: UICollectionViewFlowLayout {

    override func initialLayoutAttributesForAppearingItem(at itemIndexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
        let attr = layoutAttributesForItem(at: itemIndexPath)
        attr?.alpha = 1
        return attr
    }
}

It's necessary because by default alpha is 0, and if cells are re-created - you see blinking.

This sounds like the right solution but this method never seems to be called for me. — trapper, Jul 15 '19 at 04:31

score 1 · Answer 5 · answered Oct 20 '14 at 22:03

You can try https://github.com/ba01ei/PSTImprovedCollectionView

With this collection view, when you call reloadData, if a cell is still visible, the same cell will be returned from the queue (then you can check the data model attached to the cell and decide whether to re-render)

UICollection view reloadData cause recreate visible cell

5 Answers5