取gridview中textbox的值【C#】

<asp:GridView ID="gridView" runat="server" 
                    OnRowCommand="gridView_RowCommand">
                    <Columns>
                         <asp:TemplateField HeaderText="输入信息">
                            <ItemTemplate>
                               <asp:TextBox ID="tbx" runat="server" TextMode="MultiLine" Width="200px" Height="50px"></asp:TextBox>
                            </ItemTemplate>
                        </asp:TemplateField>
                    </Columns>
                </asp:GridView> 

protected void gridView_RowCommand(object sender, GridViewCommandEventArgs e)
        {
          string tbx = ((TextBox)gridView.Rows[Convert.ToInt32(e.CommandArgument)].FindControl("tbx")).Text;
           

        }