`CollectionView` throws `NRE` when `ItemTemplate` uses a `ViewCell` as parent

[AndreasReitberger]

Description

If using a ViewCell in the DataTemplate, the application throws an exception (NRE).

<CollectionView
    ItemsSource="{Binding Events}"
    SelectionMode="None"
    >
    <CollectionView.ItemTemplate>
        <DataTemplate>
            <ViewCell>
                <Label 
                    LineBreakMode="WordWrap" 
                    Style="{StaticResource SubHeadline}" 
                    Text="{Binding .}"
                    FontAttributes="Bold"
                    VerticalTextAlignment="Center"
                    />
            </ViewCell>
        </DataTemplate>
    </CollectionView.ItemTemplate>
    <CollectionView.EmptyView>
        <Label 
            Text="No items..."
            VerticalTextAlignment="Center"
            HorizontalTextAlignment="Center"
            />
    </CollectionView.EmptyView>
</CollectionView>

Steps to Reproduce

1. Fork the repro
2. Run it on windows (not tested any other platforms)
3. See that an exception is thrown
4. Replace ViewCell with a Grid and see that it is working afterwards

Link to public reproduction project repository

https://github.com/AndreasReitberger/MauiCollectionViewBug

Version with bug

8.0.80 SR8

Is this a regression from previous behavior?

Not sure, did not test other versions

Last version that worked well

Unknown/Other

Affected platforms

Windows, I was not able test on other platforms

Affected platform versions

No response

Did you find any workaround?

Replace the ViewCell with a Grid or something similar.

Relevant log output

No response

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[ninachen03]

This issue has been verified using Visual Studio 17.12.0 Preview 1.0 (8.0.80 & 8.0.3). Can repro on Windows platform. NET 7 have "CS9058 Feature 'collection expressions'' is not available in C# 11.0. Please use language version 12.0 or greater" so we will temporarily skip the verification of 7.

[PureWeen]

ViewCells aren't a compatible type with CollectionView they are really only a ListView concept

We should look at

1. Maybe they should be, they do have some set of useful properties for conveying size information that could help with performance.
2. throwing a better exception message

Is there any reason why you are wanting to use a ViewCell? What use case does a viewCell provide?

[AndreasReitberger]

Hi @PureWeen thanks for your reply. This is an ItemTemplate which was used in a ListView first. Then I decided to switch to a CollectionView then. As a workaround I'll update my shared ItemTemplates to do not use a ViewCell as parent control.

There is no special reason to stick to the ViewCell for me though. And yes, a better exception would be great :)

Thanks!