<ListBox.DataTemplates>
    <DataTemplate DataType="interfaces:IFileViewModel">
        <views:FileView DataContext="{Binding}" />
    </DataTemplate>
</ListBox.DataTemplates>

public sealed class FileView : ReactiveUserControl<IFileViewModel>
{
    public FileView()
    {
        this.WhenActivated(disposables => { /* Handle activation here */ });
        AvaloniaXamlLoader.Load(this);
    }
}