TableView: How to style several different TableViewRow properties depending on a single ViewModel property?

[elgonzo]

I want to change a number of TableViewRow's properties based on a single boolean property of the item ViewModel.

How can i change a bunch of TableViewRow properties based on a single property of the respective item ViewModel? What are recommended approaches that conform well to the Avalonia (MVVM) design principles?

Example item ViewModel:

public partial class ItemViewModel : ObservableObject
{
    [ObservableProperty] public partial bool HasFailed { get; private set; }
    ...
}

While i can define a style for the TableViewRow, there are no data/binding triggers supported in styles.
Since there appears to be no way for me to declare the TableViewRows used by the TableView as XAML markup, i can't conditionally use style classes like <TableViewRow Classes.ok="{Binding !HasFailed}" Classes.failed="{Binding !HasFailed}" /> either.

(EDIT: Scratch that. See follow-up comment below.) I came up with two workarounds to the problem which don't seem very appealing. One workaround i tried was implementing binding (multi-)converters together with lists of values stuffed in a resource dictionary to act as "data triggers" in the style, but that became quickly impractical and messy once several different TableViewRow properties needed to be styled conditionally. The other workaround i tried was to sub-class both TableView so that it uses a sub-classed TableViewRow that's bespoke to the particular ViewModel. (Both workarounds are technically working^TM, but in my opinion they both are cumbersome with respect to the problem they solve.)

[elgonzo]

Tinkering a bit more, i found a suitable and clean solution (or so i believe) by creating a custom attached property that allows assigning style-class bindings in a XAML style declaration. Below is my code implementing the attached property. Note however that i am rather inexperienced with Avalonia, and my current implementation might have issues i am not (yet) aware of.

public sealed class Classes : AvaloniaObject
{
    static Classes()
    {
        ClassBindingsProperty.Changed.AddClassHandler<StyledElement, ClassBindings>(OnClassBindingsChanged);
    }

    private Classes() {}


    //
    // Attached property to allow defining class bindings in styles
    //
    public static readonly AttachedProperty<ClassBindings> ClassBindingsProperty =
        AvaloniaProperty.RegisterAttached<Classes, StyledElement, ClassBindings>("ClassBindings");

    public static void SetClassBindings(StyledElement element, ClassBindings value) =>
        element.SetValue(ClassBindingsProperty, value);

    public static ClassBindings GetClassBindings(StyledElement element) =>
        element.GetValue(ClassBindingsProperty);


    //
    // Private attached property to maintain a list of class bindings bound by
    // the ClassBindingsProperty attached property for each StyledElement.
    //
    private static readonly AttachedProperty<IDisposable[]?> BoundClassBindingsProperty =
        AvaloniaProperty.RegisterAttached<Classes, StyledElement, IDisposable[]?>("BoundClassBindings");


    private static void OnClassBindingsChanged(StyledElement element, AvaloniaPropertyChangedEventArgs<ClassBindings> e)
    {
        if (e.OldValue.HasValue && element.GetValue(BoundClassBindingsProperty) is { } oldClassBindings)
            foreach (var cb in oldClassBindings)
                cb.Dispose();

        if (!e.NewValue.HasValue || e.NewValue.Value is null)
            element.SetValue(BoundClassBindingsProperty, null);
        else
        {
            var classBindings = e.NewValue.Value.Bindings;
            var newBindings = new IDisposable[classBindings.Count];
            for (int i = 0; i < classBindings.Count; ++i)
                newBindings[i] = element.BindClass(classBindings[i].ClassName, classBindings[i].Binding, "");
            element.SetValue(BoundClassBindingsProperty, newBindings);
        }
    }
}

public class ClassBindings : IAddChild
{
    [Content]
    public IList<ClassBinding> Bindings { get; } = new List<ClassBinding>();

    void IAddChild.AddChild(object child)
    {
        if (child is not ClassBinding cb)
            throw new InvalidOperationException($"Cannot add {child.GetType()} to class bindings.");

        Bindings.Add(cb);
    }
}

public class ClassBinding
{
    public required string ClassName { get; set; }

    [AssignBinding]
    public required BindingBase Binding { get; set; }
}

With the Classes.ClassBindings attached property, i can now assign style-class bindings from within the style declaration for the TableViewRow in a straightforward manner:

<TableView ItemsSource="{Binding DownloadJobViewModels}" SelectionMode="Multiple" >
    <TableView.Styles>
        <Style Selector="TableViewRow.not-started">
            <Setter Property="Background" Value="{DynamicResource SystemListMediumColor}" />
        </Style>
        <Style Selector="TableViewRow.failed">
            <Setter Property="Background" Value="LightPink" />
        </Style>

        <Style Selector="TableViewRow" x:DataType="vm:VMDownloadJob">
          <Setter Property="local:Classes.ClassBindings">
              <Setter.Value>
              <local:ClassBindings>
                  <local:ClassBinding ClassName="not-started" Binding="{Binding !DownloadJob.IsStarted}" />
                  <local:ClassBinding ClassName="failed" Binding="{Binding DownloadJob.HasFailed}" />
              </v:ClassBindings>
              </Setter.Value>
          </Setter>
        </Style>
      </TableView.Styles>
        
        ...