DropDownList OnSelectedIndexChanged is not Firing

Question

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)
    {

          int slc = Convert.ToInt32(ddlMedicalName.SelectedItem.Value);

        var orders = from order in context.Cities
                     where order.CityID == slc
                     select new { order.CityID, order.CityName};

        var lstsrc = orders.ToList();

        ddlMedicalName.DataSource = lstsrc;
        ddlMedicalName.DataTextField = "medicalname";
        ddlMedicalName.DataValueField = "cityfk";

        ddlMedicalName.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

Answer 1

Kindly change as my suggestion and try.You have to remove the below line

ddlMedicalName.DataValueField = "cityfk";

or

Make a change cityfk to medicalname and try.

ddlMedicalName.DataValueField = "medicalname";

Answer 2

I tested your code. Here are what I found so far -

ddlMedicalName_OnSelectedIndexChanged event is fired correctly.

ddlMedicalName.SelectedValue is a string value; string is not a valid datasource for ddlCity.DataSource

protected void ddlMedicalName_OnSelectedIndexChanged(object sender, EventArgs e)
{
    // Problem is the following 3 line of codes.
    ddlCity.DataSource = ddlMedicalName.SelectedValue; 
    ddlCity.DataTextField = ddlMedicalName.SelectedValue;
    ddlCity.DataValueField = ddlMedicalName.SelectedValue;

    ddlCity.DataBind();
}

Updated:

Here is how I test -

protected void Page_Load(object sender, EventArgs e)
{
    if (!Page.IsPostBack)
    {
        ddlBind();
    }
}

public class Medical
{
    public int MedicalID { get; set; }
    public string MedicalName { get; set; }
    public int CityFK { get; set; }
}

public class City
{
    public int CityID { get; set; }
    public string CityName { get; set; }
}

protected void ddlBind()
{
    var medicals = new List<Medical>()
    {
        new Medical {MedicalID = 1, MedicalName = "One", CityFK = 11},
        new Medical {MedicalID = 2, MedicalName = "Two", CityFK = 22},
        new Medical {MedicalID = 3, MedicalName = "Three", CityFK = 33},
        new Medical {MedicalID = 4, MedicalName = "Four", CityFK = 44},
    };

    ddlMedicalName.DataSource = medicals;
    ddlMedicalName.DataTextField = "medicalname";
    ddlMedicalName.DataValueField = "cityfk";

    ddlMedicalName.DataBind();

}

protected void ddlMedicalName_OnSelectedIndexChanged(object sender, EventArgs e)
{
    var cities = new List<City>()
    {
        new City {CityID = 11, CityName = "City One"},
        new City {CityID = 22, CityName = "City Two"},
        new City {CityID = 33, CityName = "City Three"},
        new City {CityID = 44, CityName = "City Four"},
    };

    int slc = Convert.ToInt32(ddlMedicalName.SelectedItem.Value);

    var orders = from order in cities
                    where order.CityID == slc
                    select new { order.CityID, order.CityName };

    var lstsrc = orders.ToList();

    ddlCity.DataSource = lstsrc;
    ddlCity.DataTextField = "CityName";
    ddlCity.DataValueField = "CityID";

    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)
{

}

Answer 3

Change:

protected void ddlMedicalName_OnSelectedIndexChanged(object sender, EventArgs e)
{

to:

protected void ddlMedicalName_SelectedIndexChanged(object sender, EventArgs e)
{

OR the opposite:

<asp:DropDownList ID="ddlCity" runat="server" AutoPostBack="true" EnableViewState="true" onselectedindexchanged="ddlCity_SelectedIndexChanged">

to:

<asp:DropDownList ID="ddlCity" runat="server" AutoPostBack="true"  EnableViewState="true" onselectedindexchanged="ddlCity_OnSelectedIndexChanged">

You are currently pointing to a handle named '..._SelectedIndexChanged' and are providing '..._OnSelectedIndexChanged'.