C#C
C#•2y ago
Brady Kelly

MAUI ContentPage binding not reflecting in child CollectionView on Android

I have this ContentPage in my MAUI app that targets only Android and iOS.

<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:models="clr-namespace:Cts.Maui.Dx.Models"
             x:Class="Cts.Maui.Dx.ApplicationListPage">
    <ContentPage.BindingContext>
        <models:ApplicationListViewModel x:Name="ViewModel" />
    </ContentPage.BindingContext>
    <ContentPage.Content>
        <CollectionView ItemsSource="{Binding Data}" x:Name="CollectionView">
            <CollectionView.Header>
                <Label Text="Header" />
            </CollectionView.Header>
            <CollectionView.ItemTemplate>
                <DataTemplate>
                    <Grid>
                        <Grid.RowDefinitions>
                            <RowDefinition />
                            <RowDefinition />
                        </Grid.RowDefinitions>
                        <Label Grid.Row="0" Text="{Binding LearnerDesc}" />
                        <Grid Grid.Row="1">
                            <Grid.ColumnDefinitions>
                                <ColumnDefinition />
                                <ColumnDefinition />
                                <ColumnDefinition />
                            </Grid.ColumnDefinitions>
                            <Label Grid.Column="0" Text="{Binding Originator}" />
                            <Label Grid.Column="1" Text="{Binding StartDate}" />
                            <Label Grid.Column="2" Text="{Binding IsLocked}" />
                        </Grid>
                    </Grid>
                </DataTemplate>
            </CollectionView.ItemTemplate>
        </CollectionView>
    </ContentPage.Content>
</ContentPage>


When I just populate the viewmodel in the page Loaded event, the collection view doesn't get bound to the viewmodel's collection, I only see the Header text.

When I explicitly bind a viewmodel instance to the collection view's ItemSource, I see the items from the viewmodel:

        var stream = await FileSystem.OpenAppPackageFileAsync("appList.json");
        var streamReader = new StreamReader(stream);
        var json = await streamReader.ReadToEndAsync();
        // Just loading the page viewmodel doesn't work.
        // ViewModel.LoadFromJson(await streamReader.ReadToEndAsync());
        var model = new ApplicationListViewModel();
        model.LoadFromJson(json);
        CollectionView.ItemsSource = model.Data;

I am raising PropertChanged for the Data property in the viewmodel:

    public IList<LicenseApplicationDto>? Data { get; private set; }
    
    public event PropertyChangedEventHandler? PropertyChanged;
    private void OnPropertyChanged([CallerMemberName] string propertyName = "") {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }

    public void LoadFromJson(string json)
    {
        Data = JsonSerializer.Deserialize<List<LicenseApplicationDto>>(json) ?? throw new InvalidOperationException("Deserialized to null");
        OnPropertyChanged();
    }

To start with, besides them being separate libraries, why should the Android and Windows CollectionView and or ContentPage bind differently?
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