I have a variable file which is collection of objects (my own class
Line). In Form_Load event I have the following code:

    DataGridTableStyle myGridStyle = new DataGridTableStyle();
    myGridStyle.MappingName = "";

    DataGridTextBoxColumn idColumn = new DataGridTextBoxColumn();
    idColumn.MappingName = "ID";
    idColumn.HeaderText = "Test";
    idColumn.Width = 240;
    myGridStyle.GridColumnStyles.Add(idColumn);

    dataGrid1.TableStyles.Add(myGridStyle);

    lineBindingSource.DataSource = file;

I have:

   public class Line
   {

       /* some stuff */

       public int ID
       {
           get { return id; }
           set { id = value; }

       }
   }

   class File : IEnumerable
   {

       /* some stuff */

       List<Line> lines = new List<Line>();

       #region IEnumerable Members

       public IEnumerator GetEnumerator()
       {
           return lines.GetEnumerator();
       }

       #endregion
   }

DataGrid1 contains all data, but I couldn't set the column width.