How do I add an unbound column to my bound datagrid

The idea is to create the ’bound’ table in your dataset, and then add an extra ’unbound’ column. The steps are to derive a custom columnstyle that
overrides Paint where you calculate and draw the unbound value. You can also override Edit to prevent the user from selecting your unbound column. Then to get your datagrid to use this special column style, you create a tablestyle and add the column styles to it in the order you want the columns
to appear in the datagrid. Here are code snippets that derive the column and use the derived column. You can download a working sample.

  // custom column style that is an unbound column
  public class DataGridUnboundColumn : DataGridTextBoxColumn
  {
    protected override void Edit(System.Windows.Forms.CurrencyManager source, int rowNum, System.Drawing.Rectangle bounds, bool readOnly, string instantText, bool cellIsVisible) 
    { 
      //do not allow the unbound cell to become active
      if(this.MappingName == ''UnBound'')
        return; 
 
      base.Edit(source, rowNum, bounds, readOnly, instantText, cellIsVisible); 
    } 
 
    protected override void Paint(System.Drawing.Graphics g, System.Drawing.Rectangle bounds, System.Windows.Forms.CurrencyManager source, int rowNum, System.Drawing.Brush backBrush, System.Drawing.Brush foreBrush, bool alignToRight)
    {
    
      //clear the cell
      g.FillRectangle(new SolidBrush(Color.White), bounds);

      //compute & draw the value
      //string s = string.Format(''{0} row'', rowNum);
      // col 0 + 2 chars from col 1
      DataGrid parent = this.DataGridTableStyle.DataGrid;
      string s = parent[rowNum, 0].ToString() + ((parent[rowNum, 1].ToString())+ ''  '').Substring(0,2);
      Font font = new Font(''Arial'', 8.25f);
      g.DrawString(s, font, new SolidBrush(Color.Black), bounds.X, bounds.Y);
      font.Dispose();
      
    }
  }

  
  //code that uses this unbound column
  private void Form1_Load(object sender, System.EventArgs e)
  {
    // Set the connection and sql strings
    // assumes your mdb file is in your root
    string connString = @''Provider=Microsoft.JET.OLEDB.4.0;data source=C:\northwind.mdb'';
    string sqlString = ''SELECT * FROM customers'';

    OleDbDataAdapter dataAdapter = null;
    DataSet _dataSet = null;

    try
    {
      // Connection object
      OleDbConnection connection = new OleDbConnection(connString);

      // Create data adapter object
      dataAdapter = new OleDbDataAdapter(sqlString, connection);
      
      // Create a dataset object and fill with data using data adapter’s Fill method
      _dataSet = new DataSet();
      dataAdapter.Fill(_dataSet, ''customers'');
      connection.Close();
    }
    catch(Exception ex)
    {  
      MessageBox.Show(''Problem with DB access-\n\n   connection: ''
        + connString + ''\r\n\r\n            query: '' + sqlString
        + ''\r\n\r\n\r\n'' + ex.ToString());
      this.Close();
      return;
    }

    // Create a table style that will hold the new column style 
    // that we set and also tie it to our customer’s table from our DB
    DataGridTableStyle tableStyle = new DataGridTableStyle();
    tableStyle.MappingName = ''customers'';

    // since the dataset has things like field name and number of columns,
    // we will use those to create new columnstyles for the columns in our DB table
    int numCols = _dataSet.Tables[''customers''].Columns.Count;

    //add an extra column at the end of our customers table
    _dataSet.Tables[''customers''].Columns.Add(''Unbound'');

    DataGridTextBoxColumn aColumnTextColumn ;
    for(int i = 0; i < numCols; ++i)
    {
      aColumnTextColumn = new DataGridTextBoxColumn();
      aColumnTextColumn.HeaderText = _dataSet.Tables[''customers''].Columns[i].ColumnName;

      aColumnTextColumn.MappingName = _dataSet.Tables[''customers''].Columns[i].ColumnName;
      tableStyle.GridColumnStyles.Add(aColumnTextColumn);

      //display the extra column after column 1.
      if( i == 1)
      {
        DataGridUnboundColumn unboundColStyle = new DataGridUnboundColumn();
        unboundColStyle.HeaderText = ''UnBound'';
        unboundColStyle.MappingName = ''UnBound'';
        tableStyle.GridColumnStyles.Add(unboundColStyle);        }
      }
      
      // make the dataGrid use our new tablestyle and bind it to our table
      dataGrid1.TableStyles.Clear();
      dataGrid1.TableStyles.Add(tableStyle);
      dataGrid1.DataSource = _dataSet.Tables[''customers''];

    }
  }