Textbox keypress event problem

private void chkBoxChange(object sender, EventArgs e)
        {

            CheckBox chk = (CheckBox)sender;
            if (chk.Checked == true)
            {
                TextBox txtBx = new TextBox();
                Rectangle rect = this.dgvItemVendor.GetCellDisplayRectangle(Convert.ToInt32(chk.Name.Split('#')[0]), -1, false);
                txtBx.Name = chk.Name.Split('#')[0] + "#-1";
                txtBx.Size = new Size(rect.Width - 20, 10);
                rect.Offset(0, 0);
                txtBx.Location = rect.Location;
                txtBx.Multiline = true;
                txtBx.Height = 18;
                this.dgvItemVendor.Controls.Add(txtBx);
                txtBx.Focus();
                txtBx.KeyPress += new System.Windows.Forms.KeyPressEventHandler(this.txtBx_txtKeyPress);
            }
        }

        private void txtBx_txtKeyPress(object sender, KeyPressEventArgs e)
        {
            
                cpattern = 'S';
                dgvItemVendor.CurrentCell = null;
                TextBox txtGetText = (TextBox)sender;
                if (e.KeyChar == Convert.ToChar(Keys.Back))
                {
                    if (txtGetText.Text != string.Empty)
                    {
                        strSearchQuery = txtGetText.Text.Substring(0, txtGetText.Text.Length - 1);
                    }
                }
                else
                {
                    strSearchQuery = txtGetText.Text + e.KeyChar;
                }
                if (e.KeyChar == '')
                {
                    if (Clipboard.ContainsText())
                    {
                        strSearchQuery = Clipboard.GetText();
                    }
                }

                if (strSearchQuery.Length > 1)
                {
                    if (strSearchQuery.StartsWith("*"))
                        cpattern = 'E';
                    if (strSearchQuery.StartsWith("*") && strSearchQuery.EndsWith("*"))
                        cpattern = 'C';
                }
                strSearchQuery = strSearchQuery.Replace("*", string.Empty);
                //if (System.Text.RegularExpressions.Regex.IsMatch(dgvItemVendor.Rows[k].Cells[Convert.ToInt32(txtGetText.Name.Split('#')[0])].Value.ToString()
                //                           , strSearchQuery
                //                           , System.Text.RegularExpressions.RegexOptions.IgnoreCase))

                for (int k = 0; k < dgvItemVendor.RowCount; k++)
                {
                    switch (cpattern)
                    {
                        case 'E':
                            dgvItemVendor.Rows[k].Visible = (dgvItemVendor.Rows[k].Cells[Convert.ToInt32(txtGetText.Name.Split('#')[0])].Value.ToString().EndsWith(strSearchQuery, true, null)) ? true : false;
                            break;
                        case 'C':
                            dgvItemVendor.Rows[k].Visible = (dgvItemVendor.Rows[k].Cells[Convert.ToInt32(txtGetText.Name.Split('#')[0])].Value.ToString().ToUpper().Contains(strSearchQuery.ToUpper())) ? true : false;
                            break;
                        default:
                            dgvItemVendor.Rows[k].Visible = (dgvItemVendor.Rows[k].Cells[Convert.ToInt32(txtGetText.Name.Split('#')[0])].Value.ToString().StartsWith(strSearchQuery, true, null)) ? true : false;
                            break;
                    }
                }
            }
            catch (Exception ex)
            {
                CustomException.ShowCustomException(ex);
            }
        }