How to select ID in GridvIew in one variable following My Code

<asp:GridView ID="GridView1" runat="server" 
                    AutoGenerateColumns="False"
                    CssClass="mGrid" 
                    DataKeyNames="" 
                    ShowFooter="true" 
                    Width="400px"
                    onrowdeleting="gvDetails_RowDeleting"
                    onrowupdating="gvDetails_RowUpdating">
        <Columns>
            <asp:TemplateField>
                <ItemTemplate>
                     <asp:ImageButton ID="imgbtnDelete" runat="server" CommandName="Cancel" ImageUrl="~/MineBlast/Image/delete.jpg" ToolTip="Cancel" Height="20px" Width="20px" />
                </ItemTemplate>
                <ItemTemplate>
                    <asp:ImageButton ID="imgbtnUpdate" CommandName="Update" runat="server" ImageUrl="~/MineBlast/Image/update.jpg"  ToolTip="Update" Height="20px" Width="20px" />
                    </ItemTemplate>
            </asp:TemplateField>
            <%-- <asp:BoundField DataField="HAU_ID" HeaderText="HAU ID" />--%>
            <asp:TemplateField  HeaderText="HAUID">
                <ItemTemplate>
                    <asp:TextBox ID="TXtHauID" runat ="server" Text='<%#Eval("HAU_ID") %>'  ></asp:TextBox>
                </ItemTemplate>
            </asp:TemplateField>
            <asp:TemplateField  HeaderText="Diesel">
                <ItemTemplate>
                    <asp:TextBox ID="TextID1" runat ="server" Text='<%#Eval("HAU_DIESELISSUED") %>'  ></asp:TextBox>
                </ItemTemplate>
            </asp:TemplateField>
            <asp:TemplateField HeaderText ="REGNO">
                <ItemTemplate >
                    <asp:TextBox ID="TextID2" runat ="server" Text ='<%#Eval("HAU_REGISID") %>'></asp:TextBox>
                </ItemTemplate>
            </asp:TemplateField>
            <asp:TemplateField HeaderText="TONNAGE">
                <ItemTemplate>
                    <asp:TextBox ID="TextID3"   runat ="server" Text ='<%#Eval("HAU_TONNAGE") %>' ></asp:TextBox>
                    </ItemTemplate>
            </asp:TemplateField>
            <asp:TemplateField HeaderText="TYPE" >
                <ItemTemplate>
                    <asp:TextBox ID="TextID4" runat ="server" Text ='<%#Eval("WORD") %>'></asp:TextBox>
                </ItemTemplate>
             </asp:TemplateField>
             <asp:TemplateField HeaderText="TRIPS" >
                <ItemTemplate>
                    <asp:TextBox ID="TextID5" runat ="server"  Text ='<%#Eval("HAU_TRIPS") %>'></asp:TextBox>
                </ItemTemplate>
             </asp:TemplateField>
             <asp:TemplateField HeaderText="CREATE DATE"  >
                <ItemTemplate>
                    <asp:TextBox ID="TextID6" runat ="server" Text ='<%#Eval("CREATED_DATE") %>' ></asp:TextBox>
                </ItemTemplate>
             </asp:TemplateField>
      </Columns>
      <FooterStyle HorizontalAlign="Center" />
      <RowStyle HorizontalAlign="Center" />
</asp:GridView>

protected void gvDetails_RowUpdating(object sender, GridViewUpdateEventArgs e)
{
        // string userid = GridView1.DataKeys[e.RowIndex].Values["HAU_ID"].ToString();  
          string  myfile  = GridView1.Rows[e.RowIndex].Cells[1].FindControl("HAU_ID").ToString () ; 
      //  int HAUID = Convert.ToInt32(GridView1.DataKeys[e.RowIndex].Values["HAU_ID"].ToString());
            
        TextBox TextID1 = (TextBox)GridView1.Rows[e.RowIndex].FindControl("TextID1");
        TextBox TextID2 = (TextBox)GridView1.Rows[e.RowIndex].FindControl("TextID2");
        TextBox TextID3 = (TextBox)GridView1.Rows[e.RowIndex].FindControl("TextID3");
        TextBox TextID4 = (TextBox)GridView1.Rows[e.RowIndex].FindControl("TextID4");
        TextBox TextID5 = (TextBox)GridView1.Rows[e.RowIndex].FindControl("TextID5");
        TextBox TextID6 = (TextBox)GridView1.Rows[e.RowIndex].FindControl("TextID6");
        //con.Open();
        //SqlCommand cmd = new SqlCommand("update Employee_Details set City='" + txtcity.Text + "',Designation='" + txtDesignation.Text + "' where UserId=" + userid, con);
        //cmd.ExecuteNonQuery();
        //con.Close();
        //lblresult.ForeColor = Color.Green;
        //lblresult.Text = username + " Details Updated successfully";
        //gvDetails.EditIndex = -1;
        //BindEmployeeDetails();  
}