Object reference not set to an instance of an object.

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ASP.NET

C#3.5

Hi all,
i am facing issue when i update the field in Gridview.Here i am trying when user click the EDIT button in that gridview dropdown will be bind.when i am binding dropdown i am getting the error.here problem is control is found.how can i resolve the issue.
Any one can u please any solution to me.
i am using .aspx code

<asp:GridView ID="Admin_Grid" runat="server" AutoGenerateColumns="False" CellPadding="4" OnRowCancelingEdit="Admin_Grid_RowCancelingEdit" OnRowEditing="Admin_Grid_RowEditing" OnRowUpdating="Admin_Grid_RowUpdating" ForeColor="#333333" GridLines="None" OnRowDataBound="Admin_Grid_RowDataBound">
           <AlternatingRowStyle BackColor="White" />
           <Columns>


               <asp:TemplateField HeaderText="FirstName">
                   <ItemTemplate>
                       <asp:Label ID="lbl_FName" runat="server" Text='<%#Eval("FirstName") %>'></asp:Label>
                   </ItemTemplate>
                   <EditItemTemplate>
                       <asp:TextBox ID="txt_FName" runat="server" Text='<%#Eval("FirstName") %>'></asp:TextBox>
                   </EditItemTemplate>
               </asp:TemplateField>
               <asp:TemplateField HeaderText="LastName">
                   <ItemTemplate>
                       <asp:Label ID="lbl_LName" runat="server" Text='<%#Eval("LastName") %>'></asp:Label>
                   </ItemTemplate>
                   <EditItemTemplate>
                       <asp:TextBox ID="txt_LName" runat="server" Text='<%#Eval("LastName") %>'></asp:TextBox>
                   </EditItemTemplate>
               </asp:TemplateField>
               <asp:TemplateField HeaderText="Organization">
                   <ItemTemplate>
                       <asp:Label ID="lbl_Organization" runat="server" Text='<%#Eval("Organization") %>'></asp:Label>
                   </ItemTemplate>
                   <EditItemTemplate>
                       <asp:TextBox ID="txt_Organization" runat="server" Text='<%#Eval("Organization") %>'></asp:TextBox>
                   </EditItemTemplate>
               </asp:TemplateField>

                <asp:TemplateField HeaderText="PhoneNumber">
                   <ItemTemplate>
                       <asp:Label ID="lbl_PhoneNumber" runat="server" Text='<%#Eval("PhoneNumber") %>'></asp:Label>
                   </ItemTemplate>
                   <EditItemTemplate>
                       <asp:TextBox ID="txt_PhoneNumber" runat="server" Text='<%#Eval("PhoneNumber") %>'></asp:TextBox>
                   </EditItemTemplate>
               </asp:TemplateField>
               <asp:TemplateField HeaderText="EmailAddress">
                   <ItemTemplate>
                       <asp:Label ID="lbl_EmailAddress" runat="server" Text='<%#Eval("EmailAddress") %>'></asp:Label>
                   </ItemTemplate>
                   <EditItemTemplate>
                       <asp:TextBox ID="txt_EmailAddress" runat="server" Text='<%#Eval("EmailAddress") %>'></asp:TextBox>
                   </EditItemTemplate>
               </asp:TemplateField>
                <asp:TemplateField HeaderText = "AIPServed">
                  <ItemTemplate>
                <asp:Label ID="lbl_AIPServed" runat="server" Text='<%# Eval("AIPServed")%>'></asp:Label>

               </ItemTemplate>
              <EditItemTemplate>

                  <asp:ListBox ID="ListBoxAIPServed" runat="server"></asp:ListBox>
       </EditItemTemplate>
        </asp:TemplateField>
                <asp:TemplateField HeaderText = "UserStatus">
                  <ItemTemplate>
                <asp:Label ID="lbl_Status" runat="server" Text='<%# Eval("UserStatus")%>'></asp:Label>
               </ItemTemplate>
              <EditItemTemplate>
             <asp:Label ID="lbl_Status" runat="server" Text='<%# Eval("UserStatus")%>' Visible = "false"></asp:Label>
         <asp:DropDownList ID = "ddl_Status" runat = "server">
       </asp:DropDownList>
       </EditItemTemplate>
        </asp:TemplateField>
               <asp:TemplateField HeaderText = "City">
       <ItemTemplate>
         <asp:Label ID="lblCity" runat="server" Text='<%# Eval("APCUserID")%>'></asp:Label>
       </ItemTemplate>
       <EditItemTemplate>
               <asp:Label ID="lblCity" runat="server" Text='<%# Eval("APCUserID")%>' Visible = "false"></asp:Label>
       <asp:DropDownList ID = "ddlCities" runat = "server">
       </asp:DropDownList>
       </EditItemTemplate>
       </asp:TemplateField>

                <asp:CommandField  ShowEditButton="True" />
           </Columns>
           <EditRowStyle BackColor="#2461BF" />
           <FooterStyle BackColor="#507CD1" Font-Bold="True" ForeColor="White" />
           <HeaderStyle BackColor="#507CD1" ForeColor="#ffffff" Font-Bold="True"/>
           <PagerStyle BackColor="#2461BF" ForeColor="White" HorizontalAlign="Center" />
           <RowStyle BackColor="#EFF3FB"/>
           <SelectedRowStyle BackColor="#D1DDF1" Font-Bold="True" ForeColor="#333333" />
           <SortedAscendingCellStyle BackColor="#F5F7FB" />
           <SortedAscendingHeaderStyle BackColor="#6D95E1" />
           <SortedDescendingCellStyle BackColor="#E9EBEF" />
           <SortedDescendingHeaderStyle BackColor="#4870BE" />
       </asp:GridView>

and aspx.cs code is

protected void Admin_Grid_RowDataBound(object sender, GridViewRowEventArgs e)
        {
            DropDownList ddlCities = (DropDownList)e.Row.FindControl("ddlCities");
            DataTable table = new DataTable();
            table.Columns.Add("APCUserID");
            //table.Columns.Add("FirstName");

            // APCUserID,FirstName,LastName,Organization,PhoneNumber,EmailAddress,AIPServed,UserID,Password,UserStatus


            //var lines = System.IO.File.ReadAllLines("test.txt");
            //System.IO.File.WriteAllLines("test.txt", lines.Take(lines.Length - 1).ToArray());

            using (StreamReader sr = new StreamReader(@"C:\Working\US_Crop\Sowmya\USCROP\AgencyProfitCommissionWebApplication\APSDataAccess\Resources\AIPlist.txt"))
            {
                while (!sr.EndOfStream)
                {
                    string[] parts = sr.ReadLine().Split(',');
                    table.Rows.Add(parts[0]);
                }
            }

            ddlCities.DataSource = table;
            ddlCities.DataTextField = "APCUserID";
            ddlCities.DataValueField = "APCUserID";
            ddlCities.DataBind();
            ddlCities.Items.FindByValue((e.Row.FindControl("lblCity") as Label).Text).Selected = true;
            
        }

Any can please share solution to me.

What I have tried:

i tried to DropDownList ddlCities = (DropDownList)e.Row.FindControl("ddlCities"); using this find the control but i am not able to find solution