Xamarin.forms: ListView items are not layout if fling is performed either at bottom or top of the view.

[DineshBabuYadav]

Hi Team,

Description

We are currently implementing a custom control with Xamarin Forms macOS support which is similar to the Xamarin Forms ListView and it is entirely based on the item Virtualization concept. In that, we are facing a strange issue in Xamarin Forms macOS i.e., if we fling the view either to top or bottom of the view, the items are not layout properly. We could not able to find the actual root cause for this issue.

Since, it is replicated in the Xamarin Forms ListView too. Can you please check this one and revert us with the actual root cause for this issue and timeline for the fix? Also, please share the workaround to resolve this issue.

Steps to Reproduce

1. Run the attached sample in macOS
2. Perform fling action upto bottom of the view.
3. The listview items are not layout as expected. (issue)

We have attached the replication procedure through the video link. You can find it below.
ListView_Issue_macOS.zip

Expected Behavior

Items need to layout properly when both fling and pan action is performed.

Actual Behavior

Items are not layout at the bottom of the view if fling is performed.

Basic Information

-Version with issue: Xamarin Forms version (v 2.5.0.280555)
Last known good version: Issue replicates even from the 2.3 version.
=== Xamarin Studio Community ===

Version 6.3 (build 864)
Installation UUID: bccf7e7d-f92c-4226-90cb-5a2028a26649
Runtime:
Mono 5.8.0.129 (2017-10/835a98d8559) (64-bit)
GTK+ 2.24.23 (Raleigh theme)

Package version: 508000129
=== NuGet ===

Version: 3.5.0.0

=== Xamarin.Profiler ===

Version: 1.6.1
Location: /Applications/Xamarin Profiler.app/Contents/MacOS/Xamarin Profiler

=== Xamarin.Android ===

Not Installed

=== Apple Developer Tools ===

Xcode 8.3.2 (12175)
Build 8E2002

=== Xamarin.Mac ===

Version: 4.2.0.20 (Xamarin Studio Community)

=== Xamarin Inspector ===

Not Installed

=== Xamarin.iOS ===

Version: 11.8.0.20 (Xamarin Studio Community)
Hash: 1c6f300e
Branch: d15-6
Build date: 2018-02-07 23:42:40-0500

=== Build Information ===

Release ID: 603000864
Git revision: 6c2f6737278ccc3e81e12276d49c0d92f975f189
Build date: 2017-04-24 11:26:01-04
Xamarin addins: d8d46e577d8507c35260ce9d73df3c33415bb214
Build lane: monodevelop-lion-d15-1

=== Operating System ===

Mac OS X 10.12.5
Darwin syncmacn11829.local 16.6.0 Darwin Kernel Version 16.6.0
Fri Apr 14 16:21:16 PDT 2017
root:xnu-3789.60.24~6/RELEASE_X86_64 x86_64

Screenshots

Reproduction Link

ListView_MacOS.zip

Regards,
Dinesh Babu Yadav

[DineshBabuYadav]

@PureWeen , we are from Syncfusion SfListView team. We use UI Virtualization concept in our control and facing this issue in our control too.

Can you please give high priority to this issue? this issue is annoying to us.

[rmarinho]

Hi @DineshBabuYadav I m not able to reproduce this issue using the sample provided. You said it happens with the normal ListView like your sample right? no custom renderer.

[DineshBabuYadav]

@rmarinho , Yes, the issue replicates with the Xamarin ListView and custom control with no custom renderer. i have attached the video too. Please have a look over the video and this one is easily replicated.

Replication Procedure:
1.Perform the scrolling action with trackpad (fling/fast scroll) so that scrollbar needs to scroll to end.

1. Perform this action repeatedly two or more time. You can see the reported issue as like in the Video.

[DineshBabuYadav]

@rmarinho , In addition to that, i have attached the custom control sample below for your reference.

In the custom scrollview, the scrolled event notification for PCL view is not triggered which have been reported in the #2141 bug report.

So, i have manually pushed the scroll notification to PCL ScrollView using custom renderer to replicate the issue to you in which a notification observer is used as like you did in the ScrollViewRenderer.

You can run the sample and follow the above replication procedure. The data is not updated properly (reported issue).

Here, you can easily replicate the issue.

CustomScrollViewIssue.zip

Thanks for your valuable time!
👍 👍 👍

[samhouts]

I do sort of see the behavior described. When I scroll down to the bottom of the list quickly, occasionally the last five items do not render immediately. It takes about a half second for them to render. I am using my touchpad to scroll down, whereas the video uses the mouse, so I assume that precision and inertia play a part. Confirming this for further investigation. Thanks!

[DineshBabuYadav]

@samhouts ,

can you please update on this.

This one is very critical for us and facing an odd experience. Can you please provide any work around for us until then.

[cnharikrishnan]

Hi Team,
Any update on this?

[Muthukumaran-G]

Hi Team,

Can you please look into this with high priority?

Thanks.

[ganesanvelusamy]

Hi Team,
Can you please take this issue as high priority? In meantime, Is there any workaround for this?

[samhouts]

This issue doesn't seem to have had any activity in a long time. We're working on prioritizing issues and resolving them as quickly as we can. To help us get through the list, we would appreciate an update from you to let us know if this is still affecting you on the latest version of Xamarin.Forms, since it's possible that we may have resolved this as part of another related or duplicate issue. If we don't see any new activity on this issue in the next 30 days, we'll evaluate whether this issue should be closed. Thank you!

[samhouts]

Since we haven't heard from you in more than 30 days, we hope this issue is no longer affecting you. If it is, please reopen this issue and provide the requested information so that we can look into it further. Thank you!