Slideshow is left when deleting file

[PhilLab]

Steps to reproduce

1. have multiple images in a folder
2. click on one, to open slide show
3. delete one
4. --> folder listing is shown

Expected behaviour

1. have multiple images in a folder
2. click on one, to open slide show
3. delete one
4. --> another image is shown

Actual behaviour

The slideshow is left and the parent folder is shown again.

Nextcloud android app version

3.32.3 . Also reproducible on master

Additional information

This functionality seems to break from time to time:

1. Initially it was fixed in When deleting image in preview activity, move to the next image #11919
2. The logic was improved and made more explicit in pull/13016
3. Somewhere it regressed again
4. Was fixed again in showDirectoryWhenDeletionCompleted set to false? #14646
5. Then it broke again. I suspect Finish PreviewImageActivity After Image Deletion #14782 , which added finishPreviewImageActivity() to the RemoveFilesDialogFragment, so that PreviewImageActivity::onRemoteOperationFinish() with the responsible logic is never called

On a secondary notice, the position handling in PreviewImageActivity::onRemoteOperationFinish() also seems to have some bugs, which we could fix in the same go:

1. When deleting the first image in a folder, it doesn't jump to the second, but the third image. If there is no third, an empty view appears
2. Sometimes (don't know yet, when) it also jumps out of the slideshow.

Lastly all this regressing and being faulty indicates we need an automated test for this.

[PhilLab]

The logic was further extended in pull/13340,
where

+        if (user.isPresent) {
+            initViewPager(user.get())
+        }

        viewPager?.setCurrentItem(nextPosition, true)
        previewImagePagerAdapter?.delete(deletePosition)

It looks like, with the re-initialization of the viewPager, changing and deleting the position is "deleting" the element twice.

In my local tests, these two changes looked promising:

1. Delete finishPreviewImageActivity() from the RemoveFilesDialogFragment

2. change the above lines to:

        if (user.isPresent) {
            initViewPager(user.get())
        } else {
            viewPager?.setCurrentItem(nextPosition, true)
            previewImagePagerAdapter?.delete(deletePosition)
        }
   

#1 fixes the main issue, #2 fixes the secondary issue of wrong jumping in the slideshow.

However, there is issues with both of these:

1. finishPreviewImageActivity() was added for a reason, in Finish PreviewImageActivity After Image Deletion #14782. I need to investigate further, how to satisfy that bug fix as well.
2. The branch when user.isPresent is false is behaving wrong. Given a folder with three images, it exhibits these issues:

• When deleting the first image, it stays in the first image.
• When deleting the second image, it goes back to the first image (as opposed to going to the next, in the other branch), and when then swiping back, it shows the just deleted image again, but with the third image's title

[PhilLab]

@alperozturk96 To understand the side effects of removing finishPreviewImageActivity() to fix the bug, I tried to reproduce what you mentioned in #14782 on the current master, but I don't even have the deletion button available inside of an end-to-end encrypted folder:

[PhilLab]

@alperozturk96 regarding my issue with not being able to test deletion of encrypted files:
I saw #15655 from @tobiasKaminsky and cherry-picked it, to test. But I couldn't reproduce the bug, when removing finishPreviewImageActivity().

Hence, I'll create a PR.