using System.Collections.ObjectModel;
using System.Collections.Specialized;
using System.Windows;
using System.Windows.Controls;
public static class DataGridExtension
    public static ObservableCollection<DataGridColumn> GetColumns(DependencyObject obj)
        return (ObservableCollection<DataGridColumn>)obj.GetValue(ColumnsProperty);
    public static void SetColumns(DependencyObject obj, ObservableCollection<DataGridColumn> value)
        obj.SetValue(ColumnsProperty, value);
    public static readonly DependencyProperty ColumnsProperty =  
           DependencyProperty.RegisterAttached("Columns",
           typeof(ObservableCollection<DataGridColumn>),
           typeof(DataGridExtension),
           new UIPropertyMetadata (new ObservableCollection<DataGridColumn>(),
           OnDataGridColumnsPropertyChanged));
    private static void OnDataGridColumnsPropertyChanged(
           DependencyObject d,
           DependencyPropertyChangedEventArgs e)
        if (d.GetType() == typeof(DataGrid))
            DataGrid myGrid = d as DataGrid;
            ObservableCollection<DataGridColumn> Columns = 
                 (ObservableCollection<DataGridColumn>)e.NewValue;
            if(Columns != null)
                myGrid.Columns.Clear();
                if (Columns != null && Columns.Count > 0)
                    foreach (DataGridColumn dataGridColumn in Columns)
                        myGrid.Columns.Add(dataGridColumn);
                Columns.CollectionChanged += delegate(object sender,
                                 NotifyCollectionChangedEventArgs args)
                       if(args.NewItems != null)
                         foreach (DataGridColumn column 
                              in args.NewItems.Cast<DataGridColumn>())
                             myGrid.Columns.Add(column);
                       if(args.OldItems != null)
                         foreach (DataGridColumn column 
                                 in args.OldItems.Cast<DataGridColumn>())
                           myGrid.Columns.Remove(column);