Bug : scrolling the Collection ad row x also scroll the collections at row x+ny with n = 1,2,3...

[mikall]

Hi,
thanks for sharing this tutorial, very useful.
Unfortunatelly I think I found a bug.
To see what I mean, please extend the number of section to
var categories = ["1", "2", "3", "4", "5", "6", "7", "8", "9", "10", "11","12", "13", "14", "15", "16", "17" ]

and add different color per collection cell (in CategoryRow.swift)

func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCellWithReuseIdentifier("videoCell", forIndexPath: indexPath) as! VideoCell
        if (indexPath.row == 0) {cell.backgroundColor = UIColor.greenColor()}
        if (indexPath.row == 1) {cell.backgroundColor = UIColor.redColor()}
        if (indexPath.row == 2) {cell.backgroundColor = UIColor.blueColor()}
        if (indexPath.row == 3) {cell.backgroundColor = UIColor.purpleColor()}
        if (indexPath.row == 4) {cell.backgroundColor = UIColor.yellowColor()}
        if (indexPath.row == 5) {cell.backgroundColor = UIColor.grayColor()}
        if (indexPath.row == 6) {cell.backgroundColor = UIColor.cyanColor()}
        if (indexPath.row == 7) {cell.backgroundColor = UIColor.clearColor()}
        if (indexPath.row == 8) {cell.backgroundColor = UIColor.blackColor()}
        if (indexPath.row == 9) {cell.backgroundColor = UIColor.brownColor()}
        if (indexPath.row == 10) {cell.backgroundColor = UIColor.darkGrayColor()}
        if (indexPath.row == 11) {cell.backgroundColor = UIColor.orangeColor()}

        return cell
    }

If you scroll row 1, also the row 7 and 13 are scrolled by the same quantity.
If you scroll row 2, also the row 7 and 14 are scrolled.

IMO is something related to the heigh of the display, n x 1.8 x display height the scroll is repeated.

I hope this can help.
Thx,
Michele

[giulio92]

I can confirm this bug happens, but I don't think it's related to the height of the device but to the reuse of UITableViewCells

[giulio92]

I'm trying to compare this project with https://github.com/AshFurrow/AFTabledCollectionView which works well but it's written using Objective-C

[mikall]

Hi, I solved this way:

1- making a struct array
2- in
func tableView(_ tableView: UITableView, didEndDisplaying cell: UITableViewCell, forRowAt indexPath: IndexPath) { //Save UX behaviour inside my Struct }
3- update cell UX in

func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {
        guard let tableViewCell = cell as? HomeTableViewCell else { return }
//update cell UX from Struct
}

I hope this help.
PS. Yes this is something related to cell reuse!

Michele

[JaapWeijland]

@mikall Could you explain what you saved exactly in the struct array? Am coping with this bug aswell!

[JaapWeijland]

Nevermind, I fixed it this way:

I made an outlet to the collectionview in my CategoryRow, so I can control the offset. What I do is saving the offset by its indexpath when a cell exits display, and load its offset by its indexpath when the cell is entering display.

Above the delegate as a field:

var offSets = [IndexPath : CGPoint]();

In the delegate:

func tableView(_ tableView: UITableView, didEndDisplaying cell: UITableViewCell, forRowAt indexPath: IndexPath) {
    if let collcell = cell as? CategoryRow{
        offSets[indexPath] = collcell.collection!.contentOffset;
    }
}

func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {

    if let collcell = cell as? CategoryRow{
        if(offSets[indexPath] == nil){
            offSets[indexPath] = CGPoint.zero;
        }
        collcell.collection!.setContentOffset(offSets[indexPath]!, animated: false);
    }
}

[mikall]

Hi,
Yes this is exactly what I did as well!