Question

I’ve found several articles about implementing expand/collapse in SL3 and SL4 which are in fact workarounds to the missing “Ancestor RelativeSource Binding”. So now SL5 is out and I would like to know how this is done in SL5.

Here is the Answer for SL4:
Expand/Collapse button in a Silverlight DataGrid

Answer 1

With the SL5 RelativeSource it’s easy to do it:

<sdk:DataGrid ItemsSource="{Binding Items}" 
   AutoGenerateColumns="False" 
   RowDetailsVisibilityMode="Collapsed">
   <sdk:DataGrid.Resources>
     <SL5:VisibilityToBoolConverter x:Key="converter"/>
   </sdk:DataGrid.Resources>
   <sdk:DataGrid.Columns>
      <sdk:DataGridTemplateColumn>
         <sdk:DataGridTemplateColumn.CellTemplate>
            <DataTemplate>
              <ToggleButton Content="Expand" 
                  IsChecked="{Binding Path=DetailsVisibility, 
                  Mode=TwoWay, 
                  RelativeSource={RelativeSource AncestorType=sdk:DataGridRow},
                  Converter={StaticResource converter}}"/>
            </DataTemplate>
          </sdk:DataGridTemplateColumn.CellTemplate>
       </sdk:DataGridTemplateColumn>
   </sdk:DataGrid.Columns>
</sdk:DataGrid>

But you will need a Visibity to Boolean converter to make it work:

public class VisibilityToBoolConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter,
        CultureInfo culture)
    {
        Visibility visibility = (Visibility)value;
        return (visibility == Visibility.Visible);
    }

    public object ConvertBack(object value, Type targetType, object parameter,
        CultureInfo culture)
    {
        bool visibility = (bool)value;
        return visibility ? Visibility.Visible : Visibility.Collapsed;
    }
}