VirtualScroll Issue Round Up

[ionitron-bot]

Original issue by @ghenry22 on 2016-10-17T00:47:41Z

I have run through all open tickets relating to virtualscroll and have compiled this list. Those tickets that still need action (unless otherwise noted) can still be reproduced. I have clearly listed duplicate tickets and tickets for issues that I can no longer reproduce with ionic2 RC1.

Hopefully this helps to clean up the open issues and can be used as a focus to target those virtualscroll issues that still exist. Most of these issues relate to ios uiwebview, although some are across all platforms.

Issues Confirmed Still Present in 3.4.2
#7734 - virtualscroll shows blank screen when used inside an ion-segment (or other conditional such as *ngIf)
#9765 - refresher component does not work with virtualscroll lists (with ionic 3.4.2 refresher cannot even be triggered if there is a virtual scroll list, cannot pull down properly)
#9975 - ScrollToTop and ScrollTo(x,y) does not work on virtualscroll list with uiwebview. create a list, add a button that will scroll to top or a to a specific location. Scroll down the list and hit the button. The display of the list will either flicker or show part of the items at the scroll destination. As soon as you try to scroll again the list display refreshes to be back where you were before pressing the button. So essential scrollTo functions do nothing. (uiwebview). This was closed but is still definitely present.
#9935 - filtering a virtualscroll list does not refocus the view port on the new list content. This issue is still present but has slightly different symptoms. I have updated the ticket with testing from v3.4.2
#12649 - using ItemSliding with VirtualScroll causes multilpe items to be slid open at once

To be confirmed (I haven't had time to test this one yet)
#11788 - When using virtual scroll with infinite scroll, when infinite scroll appends new items to the end of the list the list flickers and jumps slightly up or down.

Issue Confirmed Fixed/cannot reproduce in 3.4.2 (issues that can be closed)

Click on Details to see the fixed issues

#6999 - I believe this should be the same issue as #8267, until there is a small extra scroll not all items render after scrolling stops.
#8142 - Can be closed, tags not present, adding resolved the issue.
#8032 - Can be closed, references issue #7734, otherwise I have tested and custom components do work in virtual scroll as of RC0, image rendering of avatars inside virtualscroll is also logged under #6983 which addresses all points referenced here.
#7135 - Can be closed, virtualscroll list overlapped by header and footer. Cannot reproduce in RC0
#7116 - Can be closed, there were commits by @manucorporat which resolved this already, I can confirm that I use sliding items in large virtual scroll list and they animate and work nicely currently in RC0.
#6883 - Can be closed, initial scroll performance greatly improved, remaining issues with scroll acceleration covered in #6984
#6984 - Referred to above, also closed for scroll related performance. Issue related to ion-refresher is logged under #9765
#8267 - virtualscroll update after scrolling stops (otherwise a blank screen is shown until a small further movement is made)
#6961 - Can be closed, cannot reproduce on either ios, android or browser in RC0
#8037, #7056, #7024, #6423 (duplicates) - virtualscroll automatically scrolls to top of list on data change. Position should remain the same with the removed or added item included.
#7947 - virtualscroll inside modal not contained to viewport on iOS, long lists run off the screen
#6984 - virtualscroll on ios9 or earlier, refresher conflicts with scroll, when swiping down refresher is always triggered regardless of position in list. Means you can only scroll in one direction. Scroll acceleration also feels VERY slow compared to other platforms. No issue on android, also no issue with wkwebview and slightly better on ios10 with UIWebview.
#6983 - ion-img in virtualscroll with ion-avatar results in corrupted image display.
#6881 - custom component as virtualItem in virtualScroll leads to corrupted layout. There is a work around stated in the comments on this issue which could be added to the docs to address this.
#6974 - virtualscroll inside ion-slide results in incorrect layout (I have not been able to test this one personally)
#6512 - virtualscroll does not redraw when the list is updated to be empty. ie when search filter returns 0 results the list is not updated to show an empty list.
#6394 - ios list does not bounce when using virtualscroll. Makes it feel VERY non-native. ngfor or static lists bounce as expected.

[ghenry22]

Despite many issues being fixed virtual-scroll is still fundamentally broken in many common usage scenarios today.

It makes me a bit sad that a core Ionic component and feature remained so broken for the entire life span of Ionic2 & 3 and now the issues which have been open for going on 2 YEARS are just going to be archived here and ignored.

I love Ionic and think the product and the team do a fantastic job and continually recommend it to everyone but a bit more engagement and focus on issues like these present with virtualscroll would make a massive difference to our ability to deliver quality and consistent products quickly.