public IValueConverter GroupHeaderConverter { get; set; }

Public Property GroupHeaderConverter As IValueConverter
	Get
	Set

class GroupHeaderConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
var gr = parameter as GroupRow;
var group = gr.Group;
if (group != null && gr != null && targetType == typeof(string))
{
var desc = gr.Grid.CollectionView.GroupDescriptions[gr.Level] as PropertyGroupDescription;
return desc != null
? string.Format("{0}: {1} ({2:n0} item{3})",
desc.PropertyName,
group.Name,
group.ItemCount,
group.ItemCount == 1 ? string.Empty : "s")
: string.Format("{0} ({1:n0} items)", group.Name, group.ItemCount);
}

// デフォルト
return value;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
return value;
}
}