Extensions

public static partial class Extensions
    {
        public static T FindAncestor<T>(DependencyObject obj) where T : DependencyObject
        {
            while (obj != null)
            {
                T o = obj as T;
                if (o != null)
                    return o;

                obj = VisualTreeHelper.GetParent(obj);
            }
            return null;
        }

        public static T FindAncestor<T>(this UIElement obj) where T : UIElement
        {
            return FindAncestor<T>((DependencyObject)obj);
        }

        public static void CollapseAllRow(this DataGrid dg)
        {
            foreach (var rowItem in dg.ItemsSource)
            {
                // Ensures that all rows are loaded.
                dg.ScrollIntoView(rowItem, dg.Columns.Last());

                // Get the content of the cell.
                FrameworkElement el = dg.Columns.Last().GetCellContent(rowItem);

                // Retrieve the row which is parent of given element.
                DataGridRow row = DataGridRow.GetRowContainingElement(el.Parent as FrameworkElement);

                // Sometimes some rows for some reason can be null.
                if (row != null)
                    row.DetailsVisibility = Visibility.Collapsed;

            }

        }
    }