Low performance in TableView's scroll.

[PPacie]

First of all, great tutorial. Thanks for sharing it with the community as usual =)

Wanted to notice that the approach implemented in this issue works but has a performance side effect. I am using it in the following app, you can test it there.

When you scroll vertically in the Home screen you will notice the lags due to the reloadData() in the setCollectionViewDataSourceDelegate. I have tested commenting that line out and the vertical scroll becomes smooth.

I have an iPhone 5S, perhaps you don't notice it in most recent devices. But still that reloadData() is super expensive there.

PS: I just noticed it, in case I come up with a solution will let you know.

[ludvigeriksson]

I had a similar problem in my app where I also use UICollectionViews inside of UITableViewCells. It didn't lag, but you could actually see the cell before it reloaded, and during the time it took to reload it was unresponsive to user input.

The problem seemed to be that reloadItemsAtIndexPaths(_:), which I use instead of reloadData(), is animating the changes. To stop this I added the following inside tableView(_:willDisplayCell:forRowAtIndexPath:):

UIView.setAnimationsEnabled(false)
cell.collectionView.reloadItemsAtIndexPaths(cell.collectionView.indexPathsForVisibleItems())
UIView.setAnimationsEnabled(true)

[PPacie]

HI Ludving,

Unfortunately that approach didn't work for me. Using the reloadItemsAtIndexPaths() made the app to crash.

I've came up with a more efficient approach in the setCollectionViewDataSourceDelegate():

if collectionView.tag != row {
   collectionView.tag = row
   // Stops collection view if it was scrolling.
   collectionView.setContentOffset(collectionView.contentOffset, animated:false)
   collectionView.reloadData()
 }  

So I just reloadData() when the row changes. Still you can notice (subtle blink) when the Collection redraws that row but the overall experience is better than the original approach.

My next step is to look for a way to avoid reloading the data of the collectionView at all. Not sure if will be able to just load the data once using the approach of this tutorial.

[PPacie]

Wanted to tell you that I have completely changed the approach of the tutorial because of those TableView "scrolling blinks".

What did I do?

I could manage to load the TableView Cells just once, so the CollectionView is not being updated (aka calling reloadData()) every time you scroll up and down through the TableView.

Following the data model structure of the example, I have implemented the following method after getting the model created:

var model = [[Tweets]]()
var reusableCells = [TweetsTableViewCell]()

func createTableViewCells() {        
    for tweets in model {
        let cell = tableView.dequeueReusableCellWithIdentifier("Cell") as! TweetsTableViewCell
        //Here I set the model of the TableViewCell that will be used by the CollectionView.
        cell.tweets = tweets
        reusableCells.append(cell)
    }
    tableView.reloadData()
}

Then in the TableView Datasource:

override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {

    let cell = reusableCells[indexPath.section]
    return cell
}

Maybe this approach is not as elegant as the one of the tutorial, but now the performance of the TableView scrolling is way better, totally smooth.

Cheers, Feedback is also welcome.

[ashfurrow]

Clever approach! I hadn't thought of that. Possibly an even better solution would be to create the table views on-demand, as they are displayed for the first time. They could even be stored in an NSCache so that if the system gets low on memory, it can drop the table views and they'll get recreated the next time they're visible.

[farzadshbfn]

@PPacie Your app did not have any bugs? If there are lots of [Tweets] dequeue method will dequeue same cells. and then your setting models all wrong.

[juliensagot]

Has a solution been found for that particular issue? reloadData() is indeed really slow and has a major impact on scroll performances.

[ashfurrow]

@juliensagot not that I'm aware, but I haven't been heads-down in UIKit for a few years so it's possible someone else might know of a workaround.

[moKelani]

any solutions yet?

[PPacie]

The solution to this particular issue was https://github.com/ashfurrow/Collection-View-in-a-Table-View-Cell/issues/14#issuecomment-213578879

Nowadays, there are many ways to approach this UI by using Compositional Layouts or even SwiftUI.