Jumping to end of Content

[mmdock]

I had an issue with GLIndexedCollectionViewFlowLayout where when content offset is 0, if I were to bounce the collection (pull it to have a negative content offset on x) the offset would jump to the very end of the loaded content in the collection.

I added this:

if offsetCorrection != .greatestFiniteMagnitude {
    return CGPoint(x: proposedContentOffset.x + offsetCorrection, y: 0)
} else {
    return CGPoint(x: proposedContentOffset.x , y: 0)
}

to the final return in:

func targetContentOffset(forProposedContentOffset proposedContentOffset: , withScrollingVelocity velocity: )

Probably not the best way to handle this behavior, since I am not 100% sure why that number needs to be so high

I just wanted to bring some attention to this, as I wasn't sure if it was intended behavior to scroll to the end on a bounce at the beginning of the collection like that.

[giulio92]

Hello @mmdock, thank you for your feedback!

I have tried to place your code inside targetContentOffset(forProposedContentOffset proposedContentOffset: , withScrollingVelocity velocity: ) func to see how the code flows in one of the two if branches but as far as I can test, with regular back and forth scrolling, the only if branch that gets executed is:

return CGPoint(x: proposedContentOffset.x + offsetCorrection, y: 0)

How should I test GLIndexedCollectionViewFlowLayout to get to the other branch that you suggested?

One more question: With content offset do you refer to proposedContentOffset?

[mmdock]

@giulio92 I was finding it hard to put into words so I just upload two little vids(as gifs) with an explanation

In the above clip, you will see that when I drag my collection to the right when there are no more cells to the left, so the code return CGPoint(x: proposedContentOffset.x + offsetCorrection, y: 0) has a really large value as x causing my collection to go immediately to the final loaded cell in the collection.

The aforementioned if statement solved this issue.

Here is the new resulting behavior:

Answer: The content offset I was referring to was the content offset of the collection that happens in the first clip above. It starts at 0, when on the first cell, and I "bounce" the collection when I drag to the right trying to go to a cell on the left that doesn't exist

[giulio92]

@mmdock thank your for your further explanation!

I have managed to reproduce the issue and I have found the cause of it. The bug happens when the proposedContentOffset .x or .y values are equal to 0, causing the

targetContentOffset(forProposedContentOffset proposedContentOffset: , withScrollingVelocity velocity: )

func return to be:

return CGPoint(x: proposedContentOffset.x + offsetCorrection, y: 0)

(where offsetCorrection is .greatestFiniteMagnitude)

To fix this wrong behavior we should check if proposedContentOffset .x/.y values are greater than 0 and, if so, simply return

I will open a new Pull Request to fix this issue, with you as a credit!

[giulio92]

Pull request opened and merged on master, new version released: 1.81

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