WPF DataGridSelectedRows Extension

using System.Linq;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Input;

namespace Client.Extensions
{
    /// <summary>
    /// Extension to handle a DataGrid's SelectionChanged event to call a command
    /// <remarks>
    /// ext:DataGridSelectedRows.Command="{Binding YourCommand}"
    /// </remarks>
    /// </summary>
    public static class DataGridSelectedRows
    {
        public static readonly DependencyProperty CommandProperty =
            DependencyProperty.RegisterAttached("Command", typeof(ICommand), typeof(DataGridSelectedRows), new UIPropertyMetadata(null, OnCommandChanged));

        public static ICommand GetCommand(DependencyObject obj)
        {
            return (ICommand)obj.GetValue(CommandProperty);
        }

        public static void SetCommand(DependencyObject obj, ICommand value)
        {
            obj.SetValue(CommandProperty, value);
        }

        static void OnCommandChanged(DependencyObject target, DependencyPropertyChangedEventArgs args)
        {
            if (args.NewValue == null)
                return;

            var dataGrid = target as DataGrid;
            if (dataGrid == null)
                return;

            if (args.OldValue != null)
                dataGrid.SelectionChanged -= dataGrid_SelectionChanged;

            if(args.NewValue != null)
                dataGrid.SelectionChanged += dataGrid_SelectionChanged;
        }

        static void dataGrid_SelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            var dataGrid = sender as DataGrid;
            if (dataGrid == null)
                return;

            var command = GetCommand(dataGrid);
            if (command != null)
            {
                var cmdParam = dataGrid.SelectedItems.Cast<object>();
                if (command.CanExecute(cmdParam))
                    command.Execute(cmdParam);
            }
        }
    }
}