[Bug] (Re)Setting the ItemsSource of a CarouselView causes it to ignore the ItemsLayout

[CMehlstaeubler]

Description

My application uses the CarouselView as a main feature to show a series of opportunities to a user. The user needs to complete his user profile to a minimum degree in order to see these opportunities. Using the ItemTemplate property, I am using DataTemplateSelector to return a layout based on if the profile is completed or not. If the user does complete his profile (thereby allowing him to see the opportunities) the CarouselView does not automatically call the DataTemplateSelector again when the view is switched back to the page containing the CarouselView.

The workaround I have found to make this work is unsetting the ItemsSource and resetting it during the OnAppearing(). The code looks like this:

var tmp = OpportunityCarousel.ItemsSource;
OpportunityCarousel.ItemsSource = null;
OpportunityCarousel.ItemsSource = tmp;

This works fine on iOS, however on Android it causes the CarouselView to ignore the ItemsLayout, causing the Cards to scroll vertically, not horizontally as defined.

I have, of course, tried setting the ItemsLayout again during and after the snippet above, to no avail.

Steps to Reproduce

1. Use a ContentPage within a TabbedPage, and within that ContentPage create a CarouselView which selects a template using a DataTemplateSelector
2. Switch to another page in the TabbedPage, and update data which should cause the DataTemplateSelector to return a different DataTemplate
3. (a) With the code above (on Android): The CarouselView scrolls vertically
4. (b) Without the code above (on Android): The CarouselView scrolls horizontally, but does not update the DataTemplate to reflect the change

Expected Behavior

The CarouselView should keep using the ItemsLayout defined in the XAML/Code Behind.

I understand that the behaviour of the DataTemplateSelector is as expected (OnAppearing doesn't mean everything is redrawn), however changing the ItemsSource (which does cause the element to be redrawn) shouldn't cause the CarouselView to ignore the ItemsLayout property

Actual Behavior

When resetting the ItemsSource, the ItemsLayout is ignored

Basic Information

• Version with issue: 4.8.0.1687+400-sha.91b883e6e-azdo.4215880 (Xamarin Forms)
• Last known good version: Unknown (not tested previously)
• Platform Target Frameworks:
  • Android: 10
• Android Support Library / AndroidX Version: AndroidX
• Affected Devices: Android Simulator, real Devices

Environment

Microsoft Visual Studio Community 2019
Version 16.4.2
VisualStudio.16.Release/16.4.2+29613.14
Microsoft .NET Framework
Version 4.8.04084

Installed Version: Community

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ASP.NET and Web Tools 2019   16.4.457.38025
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Azure App Service Tools v3.0.0   16.4.457.38025
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Azure Data Lake Node   1.0
This package contains the Data Lake integration nodes for Server Explorer.

Azure Data Lake Tools for Visual Studio   2.4.1000.0
Microsoft Azure Data Lake Tools for Visual Studio

Azure Functions and Web Jobs Tools   16.4.457.38025
Azure Functions and Web Jobs Tools

Azure Stream Analytics Tools for Visual Studio   2.4.1000.0
Microsoft Azure Stream Analytics Tools for Visual Studio

C# Tools   3.4.1-beta4-19610-02+c4e5d138903b899477649a17f197abd2bcb22f9e
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Common Azure Tools   1.10
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JetBrains ReSharper 2020.2.4   Build 202.0.20200925.65451
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Mono Debugging for Visual Studio   16.5.24 (1fafd7e)
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Node.js Tools   1.5.11023.1 Commit Hash:579896f0984848d17d080c8a1c3ddff98d5ba96f
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NuGet Package Manager   5.4.0
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ProjectServicesPackage Extension   1.0
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SQL Server Data Tools   16.0.61912.09160
Microsoft SQL Server Data Tools

SyncfusionXamarinMenu Extension   1.0
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Hosting json editor into a tool window

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Visual F# Tools 10.4 for F# 4.6   16.4.0-beta.19556.5+e7597deb7042710a7142bdccabd6f92b0840d354
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Visual Studio Code Debug Adapter Host Package   1.0
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Visual Studio Tools for Containers   1.0
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VisualStudio.DeviceLog   1.0
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VisualStudio.Foo   1.0
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Xamarin   16.4.000.307 (d16-4@e031886)
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Xamarin Designer   16.4.0.464 (remotes/origin/d16-4@4abf337c3)
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Xamarin Templates   16.4.25 (579ee62)
Templates for building iOS, Android, and Windows apps with Xamarin and Xamarin.Forms.

Xamarin.Android SDK   10.1.1.0 (d16-4/f2c9364)
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Xamarin.iOS and Xamarin.Mac SDK   13.8.3.0 (0d8fe21)
Xamarin.iOS and Xamarin.Mac Reference Assemblies and MSBuild support.

Screenshots

With the Snippet above in the OnAppearing method

Without the Snippet above in the OnAppearing method

The relevant code section (ItemsLayout) defining the CarouselView in XAML

Reproduction Link

The source code contains code that should not be shared publicly; I am willing to provide the relevant sections if needed.