New Expander control causes LayoutCycle exception in winui 2.6 preview

[lhak]

Describe the bug

Testing the new Expander control and it causes LayoutCycle exceptions if a ListView is added to it.

Steps to reproduce the bug

Steps to reproduce the behavior:

1. Use the repro project
2. Scroll up and down with a touchpad
3. After a few second it will crash with a LayoutCycle exception.

Expected behavior

Screenshots

Version Info

NuGet package version:

[Microsoft.UI.Xaml.2.6.0-prerelease.210217002]

Windows app type:

UWP	Win32
Yes

Windows 10 version	Saw the problem?
Insider Build (xxxxx)
October 2020 Update (19042)	Yes
May 2020 Update (19041)
November 2019 Update (18363)
May 2019 Update (18362)
October 2018 Update (17763)
April 2018 Update (17134)
Fall Creators Update (16299)
Creators Update (15063)

Device form factor	Saw the problem?
Desktop	Yes
Xbox
Surface Hub
IoT

Additional context

ExpanderLayoutCycle.zip

[StephenLPeters]

@ranjeshj FYI

[ranjeshj]

@lhak I don't have a touch pad to test out right now, but it didn't repro with mouse. Few questions to help isolate the issue. Does it repo with keyboard/mouse or is it only when using touch pad ? Does removing the expander and just having the listview alone make it repro/not repro ? Expander is quite simple when it comes to layout, so I'm wondering if the issue is in ListView.

[lhak]

@ranjeshj I have updated the sample so that it also triggers when the expander is opened and closed very quickly with a mouse click. Two observations I have made:

• I can only reproduce it with display scaling set to 125%
• I cannot reproduce it if I set the UseLayoutRounding property of the expander content to false

ExpanderLayoutCycle2.zip

[StephenLPeters]

@gegao18 FYI

[StephenLPeters]

Moving to rendering because of the display scaling component

[robloo]

I just reproduced this in the MUXControlsTestApp with #4394 applied (also 125% display scaling).

Expanders are now within a ScrollViewer on the test page since there are too many expanders to show at once. When some controls are expanded, and then the mouse scroll wheel is used, layout cycle crash occurs.

This is definitely a show stopper.