gridview的findcontrol中存在null值，项模板混淆

我有如下网格视图的模板字段：

<asp:TemplateField ShowHeader="False">
            <EditItemTemplate>
            <asp:TextBox ID="txtEmpName" runat="server"></asp:TextBox>
                <asp:TextBox ID="txtBonus" runat="server"></asp:TextBox>
                <asp:TextBox ID="txtID" runat="server"></asp:TextBox>
            </EditItemTemplate>
                    <EditItemTemplate>
                        <asp:LinkButton ID="LinkButton1" runat="server" CausesValidation="True" 
                            CommandName="Update" Text="Update"></asp:LinkButton>
                        &nbsp;<asp:LinkButton ID="LinkButton2" runat="server" CausesValidation="False" 
                            CommandName="Cancel" Text="Cancel"></asp:LinkButton>
                    </EditItemTemplate>
                    <ItemTemplate>
                        <asp:LinkButton ID="LinkButton1" runat="server" CausesValidation="False" 
                            CommandName="Edit" Text="Edit"></asp:LinkButton>
                    </ItemTemplate>
                </asp:TemplateField>

当我在gv_RowUpdating事件中时，我想通过findcontrol获取编辑字段的值。

为此，我使用以下代码：

`TextBox txtUname = (TextBox)gv.Rows[e.RowIndex].FindControl("txtEmpName");`

但每次调试代码时，它都会在txtUname中显示null值。

问题出在哪里？

完整事件代码：

 protected void gv_RowUpdating(object sender, GridViewUpdateEventArgs e)
        {
            try
            {
                TextBox txtUname = (TextBox)gv.Rows[e.RowIndex].FindControl("txtEmpName");
                float bonus = float.Parse(gv.DataKeys[e.RowIndex].Values["bonus"].ToString());
                try
                {
                    cmd = new SqlCommand("update emp set empName=@eName");
                    cmd.parameters.AddParametersWithValue("@eName",txtUname.Text);
                    cmd.ExecuteNonQuery();
                }
                catch (Exception ex)
                {
                }
            }
            catch (Exception ex)
            {
            }
        }

编辑

protected void Page_Load(object sender, EventArgs e)
        {
            con = new SqlConnection("Data Source=192.168.51.71;Initial Catalog=WebBasedNewSoft;User ID=sa;password=prabhu");
            BindGrid();
        }
        private void BindGrid()
        {
            try
            {
                da = new SqlDataAdapter("select * from emp", con);
                DataSet ds = new DataSet();
                da.Fill(ds);
                GridView1.DataSource = ds.Tables[0];
                GridView1.DataBind();
            }
            catch (Exception ex)
            {
            }
        }
        protected void GridView1_RowUpdating(object sender, GridViewUpdateEventArgs e)
        {
            int index = GridView1.EditIndex;
            GridViewRow row = GridView1.Rows[index];
            string eName = ((TextBox)row.Cells[2].Controls[0]).Text.ToString().Trim();
            try
            {
                con.Open();
                cmd = new SqlCommand("update emp set empName='"+eName+"'",con);
                cmd.ExecuteNonQuery();
                con.Close();
            }
            catch(Exception ex)
            {
            }
        }
        protected void GridView1_RowEditing(object sender, GridViewEditEventArgs e)
        {
            GridView1.EditIndex = e.NewEditIndex;
            BindGrid();
        }
    }