[CollectionView] Crash occurs when switching CollectionView.IsVisible right after setting ItemsSource

[kubaflo]

Description of Change

The error occurs because the children's collection is modified while iterating over it. To fix this, we should iterate over a snapshot of the collection instead of the collection itself. The crash happened only on iOS and only when ItemSource is ObservableCollection

Issues Fixed

Fixes #28162

<VerticalStackLayout>
    <Button Text="Toggle visibility"
            Clicked="Button_Clicked"/>
    <CollectionView IsVisible="True"
                    HorizontalOptions="Center"
                    VerticalOptions="Center"
                    x:Name="CollectionView">
        <CollectionView.Header>
            <ContentView HeightRequest="50"
                            BackgroundColor="Green"/>
        </CollectionView.Header>
        <CollectionView.ItemTemplate>
            <DataTemplate>
                <Border StrokeShape="RoundRectangle 10"
                        Padding="20"
                        Stroke="Red">
                    <Label HorizontalOptions="Center"
                            VerticalOptions="Center"
                            Text="{Binding .}"/>
                </Border>
            </DataTemplate>
        </CollectionView.ItemTemplate>
        <CollectionView.Footer>
            <ContentView HeightRequest="50"
                            BackgroundColor="Green"/>
        </CollectionView.Footer>
    </CollectionView>
</VerticalStackLayout>

private void Button_Clicked(object sender, EventArgs e)
{
	CollectionView.IsVisible = !CollectionView.IsVisible;
	CollectionView.ItemsSource = new ObservableCollection<string> { "Item 1", "Item 2", "Item 3" };
}

[dotnet-policy-service]

Hey there @kubaflo! Thank you so much for your PR! Someone from the team will get assigned to your PR shortly and we'll get it reviewed.

[jsuarezruiz]

/azp run

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Azure Pipelines successfully started running 3 pipeline(s).

[jsuarezruiz]

Could we include a test using the sample from #28162?

[bronteq]

Hi, a similar issue also happens on Windows platform: #20037 #18481

[rmarinho]

/rebase

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Azure Pipelines successfully started running 3 pipeline(s).

[PureWeen]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 3 pipeline(s).

[PureWeen]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 3 pipeline(s).

Done.