i fill the dropdownlist dynamically from database then when i try to get the corresponding id of selected item from dropdown then it does not give me the id. i have a button haing click event which  contain the code below the .aspx 
 
this is my .aspx file 
<AddNewPopup:ModalPopupExtender ID="mp1" runat="server" PopupControlID="PanlAddNewPS" 
                        TargetControlID="lbtnAddNewPS"
                        CancelControlID="btncanceladdNewPs" BackgroundCssClass="Background" OnLoad="mp1_Load">
                    </AddNewPopup:ModalPopupExtender>
            
                    <asp:Panel ID="PanlAddNewPS" runat="server" CssClass="PopupPoliceStation panel-info" align="center" Style="display: none">
                          
                   <asp:UpdatePanel ID="udpInnerUpdatePanel" runat="Server" UpdateMode="Conditional"> 
                       <ContentTemplate>
                             <div class="panel-heading">
                            <div class="panel-title">Add New Police Station</div>
                        </div>
                        <br />
                        <div class="row">
                            <div class="col-sm-12">
                                <div class="form-group">
                                    <asp:Label runat="server" Text="Add District" Font-Bold="true" ID="Label2" CssClass="col-sm-4 control-label" ></asp:Label>
                                    <div class="col-sm-8">
                                        <asp:DropDownList runat="server" ID="ddlAddDistrict" CssClass="form-control" MaxLength="20"></asp:DropDownList>
                                      
                                         <asp:RequiredFieldValidator ID="RequiredFieldValidator9" runat="server" ControlToValidate="ddlAddDistrict" ErrorMessage="Select district" Font-Size="Small" ForeColor="Red" ValidationGroup="ValidateAddNewPoliceSation" InitialValue="Select New District"  ></asp:RequiredFieldValidator>
                                    </div> <br /><br />
                                    <asp:Label runat="server" Text="Police Station" Font-Bold="true" ID="lblPSName" CssClass="col-sm-4 control-label" ></asp:Label>
                                    <div class="col-sm-8">
                                        <asp:TextBox runat="server" ID="txtAddPSName" CssClass="form-control" MaxLength="15"></asp:TextBox>
                                         <asp:RequiredFieldValidator ID="RequiredFieldValidator8" runat="server" ControlToValidate="txtAddPSName" ErrorMessage="Required" Font-Size="Small" ForeColor="Red" ValidationGroup="ValidateAddNewPoliceSation" ></asp:RequiredFieldValidator>
                                    </div> <br /><br />
                                    
                                </div>
                            </div>
                        </div>
                        <asp:Button runat="server" CssClass="btn btn-success" ID="btnAddNewPS" Text="Add" ValidationGroup="ValidateAddNewPoliceSation" OnClick="btnAddNewPS_Click" />
                        <asp:Button CssClass="btn btn-info" ID="btncanceladdNewPs" runat="server" Text="Cancel" CausesValidation="false" OnClick="btncanceladdNewPs_Click" />
                    </ContentTemplate>
            
                            <Triggers>
                                <asp:AsyncPostBackTrigger ControlID="btnAddNewPS" EventName="Click" />
                            </Triggers>
  </asp:UpdatePanel>
                    </asp:Panel>--%>
 
code behind file       .aspx.cs
string MyQuery = string.Format("select DistrictId from District where DistrictName='{0}'", ddlAddDistrict.SelectedItem.Text);
SqlConnection con = DatabaseConnection.CreateConnection();
SqlCommand cmd = new SqlCommand(MyQuery, con);
string MyId;
MyId = cmd.ExecuteScalar() as string;
Response.Write("<script>alert('" + ddlAddDistrict.SelectedItem.Text + "')</script>");
Response.Write("<script>alert('" + MyId + "')</script>");
string insert = "insert into PoliceStation values('"+MyId+"','"+policeStation+"')";
InsertIntoDB.InsertQuery(insert);
if (InsertIntoDB.count > 0)
{
 Response.Write("<script>alert('Record added successfully')</script>");
 InsertIntoDB.count = 0;
}
else {
 Response.Write("<script>alert('Error: Record does not added')</script>");
            
}
 it does not work at all please tell me i m being stuck in this problem and make al0t of changes still insert in the second table failed because the id which i want to pick up when the user make some selection from dropdownlist.