[Bug] StackLayout's layout inside ScrollView is not updated properly when adding children

[heikow10]

The layout (especially the height) of a StackLayout or a Grid inside a ScrollView is not updated properly when adding children to the StackLayout/Grid.
When the height of the StackLayout/Grid is larger than the height of the screen after adding a child there is a gap at the end of the ScrollView. This means the StackLayout does not take the full height of its parent ScrollView.
By testing and debugging I found out that this issue is present since this change which came in in version beta-5.0.0-pre2. And the issue still occurs in the latest version (release-5.0.0-sr8).
This bug happens only on Android and not on UWP. I am not able to test with iOS.
Rotating the devices leads to a correct layout.

I found some probably related issues:
#14569, #14918, #14398, #13597

Steps to Reproduce

1. create a page with a ScrollView as content
2. add a StackLayout with vertical orientation as content of the ScrollView
3. add dynamically new children to the StackLayout till the height of the ScrollView/StackLayout is larger than the height of the screen

Expected Behavior

The height of the StackLayout is updated after each adding of a child.

Actual Behavior

The height of the StackLayout is not properly updated. When the end of the screen size is reached there is a gap at the end of the ScrollView. This means the StackLayout does not take the full height of its parent ScrollView.

Basic Information

• Versions with issue: beta-5.0.0-pre2 – release-5.0.0-sr8
• Last known good version: beta-5.0.0-pre1
• Platform Target Frameworks:
  • iOS: not able to test
  • Android: 4.4 and 10.0
  • UWP: TargetPlatformVersion: 10.0.19041.0, TargetPlatformMinVersion: 10.0.16299.0
• Android Support Library / AndroidX Version: –
• NuGet Packages: NETStandard.Library 2.0.3
• Affected Devices: HTC device with Android 4.4 and HUAWEI device with Android 10.0

Environment

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Microsoft Visual Studio Community 2019
Version 16.11.9
VisualStudio.16.Release/16.11.9+32106.194
Microsoft .NET Framework
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Build Logs

–

Screenshots

Android device (10.0 - API 29):

Reproduction Link

https://github.com/heikow10/XamarinFormsLayoutChangesBug

Workaround

call StackLayout.ResolveLayoutChanges() after calling StackLayout.Children.Add(item)