//==========================================================================================
/// <summary>
/// Auto-sizes the column widths of a DataGrid to fit the longest value.
/// </summary>
/// <remarks>The code is based upon a <a href="http://www.sellsbrothers.com/news/showTopic.aspx?ixTopic=1060">
/// blog article</a> by Chris Sells, but we update the existing column styles directly without
/// the bother of creating new ones. Columns that area already zero width are skipped and
/// remain hidden.</remarks>
/// <param name="grid">The DataGrid to process.</param>
/// <param name="pad">An additional width padding in pixels.</param>
public static void AutoSizeGrid(DataGrid grid, int pad)
{
    if (grid == null)
        return;
    if (grid.DataSource == null)
        return;
    IList list = null;
    if (grid.DataSource is IList)
        list = (IList)grid.DataSource;
    if (grid.DataSource is IListSource)
        list = ((IListSource)grid.DataSource).GetList();
    if (list.Count == 0)
        return;
    PropertyDescriptorCollection pdc = TypeDescriptor.GetProperties(list[0]);
    string mappingName = GetMappingName(list);
    DataGridTableStyle style = grid.TableStyles[mappingName];
    if (style == null)
        return;    // There is no style for the table
    using (Graphics g = grid.CreateGraphics())
    {
        // Outer loop through the columns
        for (int i=0; i<pdc.Count; i++)
        {
            string dispname = pdc[i].DisplayName;
            DataGridColumnStyle cs = style.GridColumnStyles[dispname];
            if (cs == null)
                continue;    // No grid column for this value
            if (cs.Width == 0)
                continue;    // The width is zero (leave it hidden)
            SizeF maxSize = g.MeasureString(dispname, grid.Font);
            SizeF capSize = g.MeasureString(cs.HeaderText, grid.Font);
            if (capSize.Width > maxSize.Width)
                maxSize = capSize;
            // Inner loop through the column's row values
            foreach (object o in list)
            {
                object result = pdc[i].GetValue(o);
                string s = pdc[i].Converter.ConvertToString(result);
                SizeF size = g.MeasureString(s, grid.Font);
                if (size.Width > maxSize.Width)
                    maxSize = size;
            }
            cs.Width = Convert.ToInt32(maxSize.Width) + pad;
        }
    }
}

//==========================================================================================
private static string GetMappingName(IList list)
{
    if (list is ITypedList)
        return ((ITypedList)list).GetListName(null);
    else
        return list.GetType().Name;
}