I’m trying to create a simple data grid in WinUI 3 that uses custom DataTemplate that vary for the second column, creating different formatting for the second column’s cells depending on the data type of the cell’s data. A boolean would have a CheckBox and a string would have a TextBox.

I’m extending the DataTemplateSelector class to achieve this, per this page: https://learn.microsoft.com/en-us/windows/apps/design/controls/data-template-selector

The problem is, my extension’s override DataTemplateSelectorExt.SelectTemplateCore() method shown below doesn’t even run, so I can’t even test if the template code is good. There are no errors, but the second column of the data grid only shows the namespace of the CustomInfo class: ...ViewModels.CustomInfo.

My first question is, what is preventing SelectTemplateCore() from running and providing the second column with a custom DataTemplate?

XAML

   <Page.Resources>
        <local:DataTemplateSelectorExt
            x:Key="templateselctor"
            CheckBoxTemplate="{StaticResource CheckBoxTemplateResource}"
            TextBlockTemplate="{StaticResource TextBlockTemplateResource}"
            TextBoxTemplate="{StaticResource TextBoxTemplateResource}" />

    <DataTemplate x:Key="TextBlockTemplateResource" x:DataType="x:String">
        <Grid>
            <TextBlock HorizontalAlignment="Center" VerticalAlignment="Center" />
        </Grid>
    </DataTemplate>

    <DataTemplate x:Key="TextBoxTemplateResource" x:DataType="x:String">
        <Grid>
            <TextBox Text="{x:Bind}" />
        </Grid>
    </DataTemplate>

    <DataTemplate x:Key="CheckBoxTemplateResource" x:DataType="x:Boolean">
        <Grid>
            <CheckBox HorizontalAlignment="Center" VerticalAlignment="Center" IsChecked="{x:Bind}" />
        </Grid>
    </DataTemplate>

</Page.Resources>

<Grid>
    <DataGrid
        x:Name="dataGrid1"
        ItemsSource="{x:Bind ViewModel.CustomInfoItems}" >
        <DataGrid.Columns>
            <GridTextColumn
                MappingName="CFieldDisplayName" />
            <GridTemplateColumn
                CellTemplateSelector="{StaticResource templateselctor}"
                MappingName="CFieldValue" />
        </DataGrid.Columns>
    </DataGrid>
</Grid>

Code Behind

public sealed partial class MyPage : Page
{
    public DataGridViewModel ViewModel { get; }

    public MyPage()
    {
        this.InitializeComponent();

        ViewModel = new DataGridViewModel();
    }
}


public class DataTemplateSelectorExt : DataTemplateSelector
{
    public DataTemplate TextBlockTemplate { get; set; }
    public DataTemplate TextBoxTemplate { get; set; }
    public DataTemplate CheckBoxTemplate { get; set; }

    protected override DataTemplate SelectTemplateCore(object item) 
    { //This line is never his with a breakpoint
        if (item == null)
        {
            return TextBlockTemplate;
        }
        else if (item.GetType() == typeof(string))
        {
            return TextBoxTemplate;
        }
        else if (item.GetType() == typeof(bool))
        {
            return CheckBoxTemplate;
        }
        else
        {
            return TextBoxTemplate;
        }
    }
}

ViewModel

    public DataGridViewModel()
    {
        CustomInfoItems = new ObservableCollection<CustomInfo>();
        this.GenerateCutomInfoItems();
    }

    private void GenerateCutomInfoItems()
    {
        CustomInfoItems.Add(new CustomInfo() { CFieldDisplayName = "Custom TextBox Item", CFieldValue = "String Value" });
        CustomInfoItems.Add(new CustomInfo() { CFieldDisplayName = "Custom CheckBox Item", CFieldValue = true });
    }

public class CustomInfo
{
    public string CFieldDisplayName { get; set; }
    public object CFieldValue { get; set; }
}