make a XtraGrid cell read-only on condition

using System;

using System.Collections.Generic; 

using System.ComponentModel; 

using System.Data; 

using System.Drawing;  

using System.Text; 

using System.Windows.Forms; 

using DevExpress.XtraGrid.Views.Grid; 

namespace ReturnForm

 {

      public partial class Form1 : Form {

          public ReturnForm()   
          {

              InitializeComponent();

          }

          private void Form1_Load(object sender, EventArgs e)
          {

              FillDataSource();

          } 

          private void FillDataSource()

          {
              dtProducts = dsProducts.dtProductsTableAdapter.Fill( 

                                                this.dsProducts.dtProducts);
          }
          private bool IsShipToUSCanada(GridView view, int row)
          {
              try

            {

                    string val = Convert.ToString(

                                view.GetRowCellValue(row, "ShipCountry"));

                  return (val == "US" || val == "Canada");

              }

             catch( )

            {

                  return false;

            }

      }

         private void grvProducts_ShowingEditor(object sender, CancelEventArgs e)

        {

              if(gridView1.FocusedColumn.FieldName == "IsFreeShipping" 

                 && IsShipToUSCanada(grvProducts, grvProducts.FocusedRowHandle))

                  e.Cancel = true;

       }

        private void grvProducts_RowCellStyle(object sender,

                      DevExpress.XtraGrid.Views.Grid.RowCellStyleEventArgs e)

        { 

             if(e.Column.FieldName == "IsFreeShipping" 

                               && IsShipToUSCanada(grvProducts, e.RowHandle))

            {

                  e.Appearance.BackColor = Color.LightGray; 

             } 

         }

      }

  }