DropDownList OnSelectedIndexChanged is not Firing

DropDownList OnSelectedIndexChanged is not Firing

My main purpose, populating the ddlCity DropDownList according to the
ddlMedicalName selection. But my main problem is, although I try almost
every solution to that problem, I couldnt make it firing
ddlMedicalName_OnSelectedIndexChanged .
I know, there is plenty of questions and answers about that problem, I
have tried almos every one of them but still it doesn't work. I have read
that EnableStateView=True should be applied not only to DropDownList but
also to the whole page, So I have added the following code to the
Web.Config:
<system.web>
<pages styleSheetTheme="MainTheme" enableViewState="true"/>
And here is my code behind:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;
using System.Data;
using System.Configuration;
namespace MedicalBootStrap
{
public partial class WebForm1 : System.Web.UI.Page
{
Entity.medicaldbEntities context = new Entity.medicaldbEntities();
protected void Page_Load(object sender, EventArgs e)
{
if (!Page.IsPostBack)
{
ddlBind();
}
}
protected void ddlBind()
{
var orders = from order in context.Medicals
select new { order.MedicalID, order.medicalName,
order.CityFK };
var lstsrc = orders.ToList();
ddlMedicalName.DataSource = lstsrc;
ddlMedicalName.DataTextField = "medicalname";
ddlMedicalName.DataValueField = "cityfk";
ddlMedicalName.DataBind();
}
protected void ddlMedicalName_OnSelectedIndexChanged(object sender,
EventArgs e)
{
ddlCity.DataSource = ddlMedicalName.SelectedValue;
ddlCity.DataTextField = ddlMedicalName.SelectedValue;
ddlCity.DataValueField = ddlMedicalName.SelectedValue;
ddlCity.DataBind();
}
protected void ddlRegion_SelectedIndexChanged(object sender, EventArgs e)
{
}
protected void ddlCity_SelectedIndexChanged(object sender, EventArgs e)
{
}
protected void SearchButton_Click(object sender, EventArgs e)
{
}
}
}
And here is aspx:
<%@ Page Title="" Language="C#" MasterPageFile="~/Site.Master"
AutoEventWireup="true" CodeBehind="MedizinischeLeistungen.aspx.cs"
Inherits="MedicalBootStrap.WebForm1" EnableViewState="true" %>
<asp:Content ID="Content1" ContentPlaceHolderID="HeadContent" runat="server">
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="MainContent"
runat="server" EnableViewState="true">
<table id="SearchTable">
<tr>
<td>Medizinische Leistung</td>
<td>Region</td>
<td>Stadt</td>
</tr>
<tr id="SearchDropDown">
<td>
<asp:DropDownList ID="ddlMedicalName" runat="server"
EnableViewState="true"
AutoPostBack="True" AppendDataBoundItems="true"
OnSelectedIndexChanged="ddlMedicalName_OnSelectedIndexChanged">
<asp:ListItem Value="" Selected="True"> - Product - </asp:ListItem>
</asp:DropDownList>
</td>
<td>
<asp:DropDownList ID="ddlRegion" runat="server" AutoPostBack="true"
EnableViewState="true"
onselectedindexchanged="ddlRegion_SelectedIndexChanged">
<asp:ListItem Value="" Selected="True"> - Product - </asp:ListItem>
</asp:DropDownList>
</td>
<td>
<asp:DropDownList ID="ddlCity" runat="server" AutoPostBack="true"
EnableViewState="true"
onselectedindexchanged="ddlCity_SelectedIndexChanged">
<asp:ListItem Value="" Selected="True"> - Product - </asp:ListItem>
</asp:DropDownList>
</td>
<td>
<asp:Button ID="SearchButton" runat="server" Text="Suche"
onclick="SearchButton_Click" />
</td>
</tr>
</table>
</asp:Content>
Any help would be appreciated