CODEWITHSUNDEEP
c#asp.net
AaA
AaA

Reputation: 3694

First Item in dropdownlist doesn't fire SelectedIndexChanged at all

I have following simple code:

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="testForm.aspx.cs" Inherits="Orbs.testForm" %>
<html>
<body>
    <form id="form1" runat="server">
        <asp:DropDownList ID="dropdown1" runat="server" AutoPostBack="true" OnSelectedIndexChanged="dropdown1_SelectedIndexChanged" ViewStateMode="Enabled">
            <asp:ListItem Value="1" Text="Item 1" />
            <asp:ListItem Value="2" Text="Item 2" />
            <asp:ListItem Value="3" Text="Item 3" />
            <asp:ListItem Value="4" Text="Item 4" />
            <asp:ListItem Value="5" Text="Item 5" />
        </asp:DropDownList>
        <asp:Label runat="server" ID="label1"></asp:Label>
    </form>
</body>
</html>

And this is my code behind

using System;

namespace Orbs {
    public partial class testForm: System.Web.UI.Page {
        protected void Page_Load(object sender, EventArgs e) {
            label1.Text = "???!!";
        }

        protected void dropdown1_SelectedIndexChanged(object sender, EventArgs e) {
            label1.Text = "Fired on " + dropdown1.SelectedValue;
        }

    }
}

When the first time I enter the page, label1 shows '???!!'. Now I select an item from dropdown and label1 shows correct value but when I select first item in dropdown, it again shows ???!! instead of Fired on 1

Where I'm doing wrong?

Edit: I noticed if I add Selected="True" to any of the items in the dropdown, that item becomes victim and won't fire the event!

Upvotes: 11

Views: 16408

Answers (7)

Ganesh Jadhav
Ganesh Jadhav

Reputation: 2848

In my case, this happened because I had referred to that dropdown using a local dropdownlist variable, and disposed off that variable at the end of a function. I was adding the first item to the dropdownlist after setting a datasource. Took me 2 hours to find this, and worked perfectly after I removed the dispose call.

Upvotes: 0

Bisher Andoura
Bisher Andoura

Reputation: 109

I had the same problem, but I solved it by calling onindexchanged function manually, like this:

ddl_SelectedIndexChanged(null, null);

I know this may not be the perfect way but it's working for me.

Upvotes: 1

goodeye
goodeye

Reputation: 2449

This question covers all the possibilities better than other posts out there, so I'm adding this explicit answer. In my case @Edyn's comment worked, even though the original problem already has this:

Set ViewStateMode="Enabled" on the dropdown control itself.
I also set it on the page declaration at the top of the page, just in case.

This is .Net 4.0, so perhaps something was changed (but certainly not fixed nicely).

Upvotes: 1

AaA
AaA

Reputation: 3694

I solved the problem myself,

I read somewhere that turning off the ViewStateMode will cause DropDownListnot work properly. In my web application I had to turn off ViewStateMode to achieve some global task and turn it on case by case.

Somehow turning on ViewStateMode on DropDownList is not working, I even tried turning on ViewStateMode for page and master page but still DropDownList didn't work. it only worked when I turned on ViewStateMode in web.config.

As turning on ViewStateMode in web.config is not an option, I found and alternate solution. I'm including it here hoping it help someone.

  • Add a HiddenField to your form.
  • In Page_Load compare value of HiddenField with Request.Forms[DropDownList1.UniqueID]
  • if they are different, call SelectedIndexChanged manually
  • Set the value of HiddenField to value of Request.Forms[DropDownList1.UniqueID].

Upvotes: 4

hentie
hentie

Reputation: 181

For Anyone still having the problem; I solved it in a different, yet easier way: Just add a dummy ListItem to the start of the DropDownList and set that item's Enabled property to false. i.e.

<asp:DropDownList ID="dropdown1" runat="server" AutoPostBack="true" OnSelectedIndexChanged="dropdown1_SelectedIndexChanged" ViewStateMode="Enabled">
        <asp:ListItem Value="" Text="" Enabled="false" />
        <asp:ListItem Value="1" Text="Item 1" />
        <asp:ListItem Value="2" Text="Item 2" />
        <asp:ListItem Value="3" Text="Item 3" />
        <asp:ListItem Value="4" Text="Item 4" />
        <asp:ListItem Value="5" Text="Item 5" />
    </asp:DropDownList>

Upvotes: 18

ZoharAdar
ZoharAdar

Reputation: 474

Had the same issue - SelectedIndexChanged doesn't fire when selecting the first option, My not clean solution was (not sure that was so smart but it work for me),

At the Page_Load I added the follow script:

if (!IsPostBack)
        {

            //bind data first time
        }
        else
        {
            int ddlSortByValue = int.Parse(ddlSortBy.SelectedValue);
            if (ddlSortByValue == 0)
            {
                ddlSortBy_SelectedIndexChanged(this, EventArgs.Empty);
            }

        }

That way I force the SelectedIndexChanged event to fire up

Upvotes: 1

TheGeekYouNeed
TheGeekYouNeed

Reputation: 7539

This is happening because you are setting the label to "???!!" every page event.

You need to modify your page load to detect f a Postback has not occured.

    protected void Page_Load(object sender, EventArgs e) {
        if(!IsPostBack)
        {
            label1.Text = "???!!";
        }
    }

Upvotes: 0

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