DropDownList's SelectedIndexChanged event not

问题:

I have a DropDownList object in my web page. When I click on it and select a different value, nothing happens, even though I have a function wired up to the SelectedIndexChanged event. I'll try and post my code here as orderly as possible:

First, the actual object's HTML code:

<asp:DropDownList ID="logList" runat="server" 
       onselectedindexchanged="itemSelected">
</asp:DropDownList>

And this is that function, itemSelected:

protected void itemSelected(object sender, EventArgs e)
{
    Response.Write("Getting clicked; " + sender.GetType().ToString());
    FileInfo selectedfile;
    Response.Write("<script>alert('Hello')</script>");
    foreach (FileInfo file in logs)
    {
        if (file.Name == logList.Items[logList.SelectedIndex].Text)
        {
            Response.Write("<script>alert('Hello')</script>");
        }
    }
}

None of the Responses appear, and that portion of JavaScript is never run. I've tried this on the latest 3.6 version of Firefox, as well as Internet Explorer 8. This is being served from a Windows Server 2003 R2 machine, running ASP.Net with the .NET Framework version 4.

If anyone can help, that would be great.

回答1:

Set DropDownList AutoPostBack property to true.

Eg:

<asp:DropDownList ID="logList" runat="server" AutoPostBack="True" 
        onselectedindexchanged="itemSelected">
    </asp:DropDownList>

回答2:

try setting AutoPostBack="True" on the DropDownList.

回答3:

I know its bit older post, but still i would like to add up something to the answers above.

There might be some situation where in, the "value" of more than one items in the dropdown list is duplicated/same. So, make sure that you have no repeated values in the list items to trigger this "onselectedindexchanged" event

回答4:

Add property ViewStateMode="Enabled" and EnableViewState="true" And AutoPostBack="true" in drop DropDownList

For more details click here

回答5:

Also make sure the page is valid. You can check this in the browsers developer tools (F12)

In the Console tab select the correct Target/Frame and check for the [Page_IsValid] property

If the page is not valid the form will not submit and therefore not fire the event.

回答6:

For me answer was aspx page attribute, i added Async="true" to page attributes and this solved my problem.

<%@ Page Language="C#" MasterPageFile="~/MasterPage/Reports.Master"..... 
    AutoEventWireup="true" Async="true" %>

This is the structure of my update panel

<div>
  <asp:UpdatePanel ID="updt" runat="server">
    <ContentTemplate>

      <asp:DropDownList ID="id" runat="server" AutoPostBack="true"        onselectedindexchanged="your server side function" />

   </ContentTemplate>
  </asp:UpdatePanel>
</div>

回答7:

insted of what you have written code you can write it directly in the SelectedIndexChanged event of the dropdownlist control e.g.

protected void ddlleavetype_SelectedIndexChanged(object sender, EventArgs e)
{
***************
***********
****
}