CollectionView working in debug but not in release in .NET MAUI

Question

I have the following

<CollectionView Margin="5" ItemsSource="{Binding Subjects}">
    <CollectionView.ItemsLayout>
        <GridItemsLayout Orientation="Vertical" Span="2" />
    </CollectionView.ItemsLayout>
    <CollectionView.EmptyView>
        <ContentView>
            <Label Text="No subjects entered yet..." />
        </ContentView>
    </CollectionView.EmptyView>
    <CollectionView.ItemTemplate>
        <DataTemplate>
            <Border MaximumWidthRequest="300">
                <Border.StrokeShape>
                    <RoundRectangle CornerRadius="10" />
                </Border.StrokeShape>
                <Border.GestureRecognizers>
                    <TapGestureRecognizer Command="{Binding Source={RelativeSource AncestorType={x:Type vm:MainPageViewModel}}, Path=DeleteSubjectCommand}" CommandParameter="{Binding .}" />
                </Border.GestureRecognizers>
                <Label Margin="5" Text="{Binding .}" />
            </Border>
        </DataTemplate>
    </CollectionView.ItemTemplate>
</CollectionView>

The problem is that the <Label Margin="5" Text="{Binding .}" /> is blank in release in my .NET MAUI Android application while in debug, it is populated and the gesture recogniser works. When I add items to the list, the correct number of items appears so it leads me to think that there is something happening with the label highlighted above.

How do I solve this?

This "Subjects" is ObservableCollection with String used as generic type, right? There are many issues with CollectionView, but posting some C# code around your XAML wont hurt. — H.A.H.
– H.A.H., Commented Jan 30, 2023 at 11:23
* If you do ... Text="This is a test" />, does the text show? * If you remove the border and its recognizer, so datatemplate is simply <Label ... />, does the bound text show? * Add c# code: Subjects declaration, code that sets Subjects or adds its items * is that code called from constructor? OnAppearing? inside an async method? — ToolmakerSteve
– ToolmakerSteve, Commented Jan 30, 2023 at 20:31
I did the second thing. And still wouldn't appear. This is a test would appear in debug and not in release mode. — Tanaka Mawere
– Tanaka Mawere, Commented Jan 31, 2023 at 13:01

Julian · Accepted Answer · 2023-04-11 11:21:03Z

11

Replace:

<DataTemplate>

With:

<DataTemplate x:DataType="{x:Type x:String}">

Do not ask me why.

edited Apr 11, 2023 at 11:21

Julian

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answered Jan 30, 2023 at 14:32

H.A.H.

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6 Comments

Tanaka Mawere Over a year ago

I'd really love to ask why😂

H.A.H. Over a year ago

@TanakaMawere I do not know. I have few releases already, and I have never faced your problem before. The thing that I noticed, is that I always specify the DataType of my templates. Removed the DataTypes. Tested in release, some of my CollectionViews became blank. Set the background, it turns out they are there, the items are not loading. Change to debug - items get rendered again. I could not believe it.

H.A.H. Over a year ago

Please, just give it a try.

bebenlebricolo Over a year ago

Can't believe it. This is still true to this day (19th Jan 2024). With .net 8 and all the "new" stuff. Makes no sense. Thank your for that answer, it helped me just as well !

bebenlebricolo Over a year ago

By the way, I created a bug ticket on dotnet maui Repo thanks to this answer; as I'm having the exact same issue and your suggestion is a valid workaround for this. Thankls again @H.A.H. We'll see if that helps.

|

User1 · Accepted Answer · 2024-02-16 11:37:46Z

I've ran into the same issue, the more generic solution if your collection view binding type is not known at compile time is to bind to x:DataType="{x:Type x:Object}"

This is useful is your making components that bind to collections and can't hard-code the datatype in advance

<CollectionView.ItemTemplate>
    <DataTemplate x:DataType="{x:Type x:Object}">
        <Grid x:Name="OuterHostGrid" ColumnDefinitions="*, 60">
            <Label
                FontAttributes="None"
                FontFamily="PoppinsMedium"
                FontSize="13"
                Text="{x:Binding .}"
                TextColor="{AppThemeBinding Light=Black,
                                            Dark=White}"
                VerticalOptions="Center" />
           </Grid>
     </DataTemplate>
</CollectionView.ItemTemplate>

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